9th Millennium International Symposium on
Flow Visualization
Edinburgh, Scotland, UK
August 22-25, 2000
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| Authors | Title | Keywords | Abstract |
| A. Aboulazm. | VISUALIZATION OF ICE FLOES DURING SHIP-ICE INTERACTION. | visualization, ice floes. | This paper describes a study of the problem of ship- ice interaction in ice-covered waters. The study covers full scale testing and visualization of ice floes during ship advance through ice in different ice conditions and at different ship speeds. Results of ice floe visualization have been used to develop an understanding of the motion responses of the ice floes during the ship-ice encounter. This understanding is essential for the development of accurate and reliable numerical and computer simulation of ship motions in ice, and as such, this paper also describes some developments in numerical simulations in this area . |
| Abrukov, V.S., Andreev I.V., Kocsheev I.G. | INTERFEROMETRIC TECHNIQUES AND AUTOMATIC DATA PROCESSING IN COMBUSTION, HEAT TRANSFER AND GAS DYNAMICS | interferometry, data processing, new automation system | The wide potentialities
of interferometry for combustion, heat and gas dynamic investigations have
already been demonstrated . Interferometric methods can be used now for
the measurement of very various characteristics: flame temperature field,
velocity field of non-stationary gas flow, heat release power during ignition
process of propellant, effective coefficient of complex heat transfer, and
other parameters. Practical realization of a broad possibilities of interferometric methods requires to automate a process of measurement, first of all, for a stage of interferogram decryption (getting data about phases difference distribution in interferogram, plane and eikonal value). The authors have created automated procedures that permit the realization of practically all possibilities of interferometric technique. The use of these procedures and TV-registration can make interferometric tools increasingly viable for use in the scientific research. The present work generalizes some previous results of authors and presents a principally new optimum automation procedure that can be used for interferometric measurement. It use the presentation about interferogram as collections of black and white pixels and allows to define:
|
| A. Amoresano, G. Langella and C. Noviello. | EXPERIMENTAL ANALYSIS OF TWO PHASE FLOW BEHAVIOR INSIDE A CENTRIFUGAL PUMP. | two phase flow, centrifugal pump, high speed CCD cameras. | To investigate how two phase flow (water and air) changes the performance of a centrifugal pump, tests were carried out using a pump which had a transparent suction line and impeller flange. The tests were carried out varying, with time, the water flow rate/air flow rate ratio. Using a CCD camera, the behavior of the air bubbles was followed inside the suction line and their distribution monitored inside the ducts of the impeller. Using a differential, compound, balancing motor the momentum was correlated with the dispersed energy and related to the particular two phase flow inside the impeller. |
| Aroussi A, Amr Hassan, Clayton B, Abdul Nour B and Rice E. | EFFECTS OF VEHICLE WINDSHIELD DEFROSTING AND DEMISTING PROCESS ON PASSENGER COMFORT. | piv, lda, thermal imaging, hot bulb probe, numerical simulation, car windshield, demisting. | Maintaining adequate visibility at all times, through a vehicle windshield, is critical to its safe usage. The ability of the windshield defrost and demist system to quickly and completely melt ice on the outer windshield surface and remove mist formed on the inner surface is therefore of paramount importance. The objective of this paper is to investigate the fluid flow and heat transfer on the windshield of a full-scale vehicle. The visualisations results presented are from numerical simulations validated by experiment using PIV LDA, Thermal Imaging and Hot Bulb Probe. |
| J. Baranski, W. Blasiak and J. Stasiek. | FLOW AND COMBUSTION VISUALIZATION BY USING PHYSICAL AND MATHEMATICAL MODELING FOR OPTIMIZATIONS AND REDESIGN OF INDUSTRIAL BOILERS. | combustion, physical model, mathematical model, industrial boiler. | Physical modeling is the term used to describe the experimental methods, involving small-scale isothermal water models for simulate and study nonisothermal flow, combustion, mixing and heat transfer occurring in real plant. The model need to be a full three-dimensional replica of the plant and must be used with certain, well established scaling and similarity criteria, which makes possible to visualize real industrial processes properly. Mathematical modeling is the numerical simulation of the interrelated combustion, fluid flow, mixing and heat transfer phenomena which govern the thermal behavior of the plant. The model is often written in the form of a computer program and embodies a system of mathematical equations, with defined input and output. A combination of physical and mathematical modeling is established technique to achieve high accuracy of simulation for optimization and redesign of industrial combustion chambers like boilers, furnaces or burners to reduce emissions and to get a more rapid and efficient mixing of reactants. This paper presents application of in three dimensions physical and mathematical modeling to study, optimization and modernization a large scale 250 MW pulverized fuel (PF) fired boiler to visualize the flow pattern, mixing and combustion processes. |
| W. Blasiak. | MODELLING AND VISUALIZATIONS OF REACTING JET FLOWS. | jets, modelling, combustion. | Free turbulent jets are used to control mixing in all types of thermal and flow reactors. The example studied in this work is the application of multi-jets in combustion chambers. In this case usually many interacting turbulent jets are used to control mixing thus combustion processes. The modelling technique discussed here is so called physical modelling. This modelling technique uses weak water solutions of acid and alkali in small-scale Plexiglas models to simulate the non-isothermal and chemically reacting flows. Of course, many assumptions and simplifications are made to allow the physical modelling of such a complex chemical and non-isothermal process. In this work theoretical basis of the physical modelling applied to a single turbulent jet in a cross-flow are discussed. Particularly approaches to modelling of the gas jet and the two-phase (gas-particles and gas-droplets) jets are analysed. Finally application of the physical modelling to the multi-jets in a cross-flows is shown. Two different configurations of flow are considered. These are two types of multi-jet flow in a cross-flow; with a vertical straight and rotating cross-flow respectively. |
| A. Bogdanov, E. Zudilova and D. Shamonin. | 3D VISUALISATION OF CONVECTIVE CLOUD SIMULATION. | high performance computing, simulation, convective flows, numerical visualization. | The paper is devoted to the complex process beginning by obtaining numerical data while solving a scientific problem and completing by the creation of the demo for illustrating the final solution in graphical form. Seven main stages of the following process are distinguished. The visualized results to be represented were obtained for the simulation of mature convective clouds. The process of numerical simulation was based on the solution of equations describing the axisymmetric turbulent flow of compressible two-phase, two-component medium taking into account condensation of water vapour and precipitation formation. The model includes a module describing the processes of aerosol transfer and scavenging. It provides the ability for calculating the parameters for smoke clouds formed by volcanic eruptions and for estimating the amount of the pollution deposited on the surface and transported into the upper layers of the troposphere and into the stratosphere. All calculations were carried out using HP CONVEX supercomputers. Then the numerical data was converted using Geomview - special animation tool oriented for 3D visualization under IRIX 6.2 (SGI Octane workstation). It became possible thanks to the additional module written in C/C++ and aimed to the converting data of special formats into the series of graphical images. As a result, the 3D animation film in three projections was elaborated. The paper is to be widely illustrated with all presented materials being the results of prolonged collaborative team research. |
| K. T. Chan, Y. J. Li and R. M. C. So. | PARTICLE IMAGE ABERRATIONS OF OFF-AXIS HOLOGRAPHY. | off-axis holography, holographic grating, image aberrations. | Two approaches have been proposed to analyse the particle image aberrations of off-axis holography. One is based on the traditional wave-front mismatching theory. Another involves the holographic grating theory. Calculations show that aberration severity is dependent on the location of the particles relative to the imaging system. Experimental results agree with the predictions, showing different image quality at different real image regions. |
| S. M. Chang and K. S. Chang. | SHOCK-VORTEX INTERACTION IN THE SHEAR LAYER OF A FLAT PLATE. | shock-vortex interaction, holographic interferometry, shadowgraphy, CFD. | The interaction of a moving shock and a vortex behind a flat plate is visualized using experimental and numerical techniques. The flat plate is installed horizontally in a shock tube and connected to an upstream shock splitter plate designed by Whitham's theory and its method of characteristics. The initial shock of Ms=1.34, entering the splitter, is accelerated to Ms=1.41 in the upper space of the flat plate and decelerated to Ms=1.22 in the lower space. The diffraction of the faster upper shock at the end of the flat plate generates a nearly isolated vortex, which interacts with the slower lower shock as it arrives. Holographic interferometry and shadowgraphy are used for the experimental visualization. The Navier-Stokes equations are also numerically integrated with high-resolution TVD method using quadrilateral unstructured adaptive grid. The experimental images of shock-vortex interaction are remarkably clear compared with other existing similar experiments. The emission of quadruple type acoustic waves is clearly visualized. |
| A.M. Choulmeister, T.V. Bazhenova, V.V. Golub, D.A. Nikitin. | THE DYNAMICS OF SUPERSONIC VORTEX RING IN HOT AND COLD IMPULSIVE JETS. | vortex ring, impulsive jet, interferometry,Schlieren,numerical visualization. | The supersonic vortex rings in hot and cold impulsive jets were investigated using optical and numerical methods. The hot jet was produced by using a shock tube. The working gas heated behind the reflected shock wave in a shock tube was discharged through the nozzle into a test chamber. The working gas at ambient stagnation temperature was used to produce the cold jet. The low pressure chamber of a shock tube was used as reservoir. The time evolution of supersonic vortex rings was recorded using a Schlieren device and interferometer. To obtain 72 images in one experiment a high speed camera was used, with the frame size 16 x 22 mm, and interval between the images of 10 microseconds. An interferometer with narrow reference beam was assembled on the basis of the Schlieren device. A ruby laser was used as the light source, having a pulse duration 30 ns. The numerical modelling of impulsive jets was based on axisymmetric Euler equations. The equations were solved by Godunov's method having second order accuracy. The physical mechanism of vortex ring formation was revealed for hot and cold jets. |
| Frédéric DANBON, Stéphane VIAZZO, Camille SOLLIEC. | ANALYSIS OF THE AERODYNAMIC OF A BUTTERFLY VALVE USING EXPERIMENTAL AND NUMERICAL FACILITIES. | applied aerodynamic, experiments, computational fluid dynamic, butterfly valve. | Many industrial facilities use butterfly valves to check the flow, or as a safety device. The main advantages of these valves are their simplicity, their low price, their high speed of closing and the small pressure drop which they produce when they are completely open. The knowledge of the aerodynamic torque produced around the axis of the valve is of a great interest to calculate the power of the actuator. It is difficult to estimate this torque because the fluid flow around the valve depends strongly on its shape and on the geometry of the circuit. PIV and visualizations of the flow structure, pressure distribution on the valve surface and velocity measurements achieved on a test bench are compared with those calculated by numerical simulations performed on a 2D and a 3D model of the valve. This research shows the ability of present day CFD software to predict the aerodynamic of the butterfly valve. It also specifies the assistance brought by numerical simulations in the comprehension of the flow structure and in the choice of the best methods of measurements to use to extract the maximum of information from the experiments. |
| G. De Stefano and L. Iuspa. | A CLUSTER ORIENTATED GENETIC ALGORITHM FOR VORTEX IDENTIFICATION. | genetic algorithms, vortex identification, multi-objective opimization. | The identification of vortical structures can be performed with the aid of a cluster orientated genetic search. Different vortex identification criteria can be successfully adopted in conjunction with genetic algorithms. One of the advantages of this approach for vortex detection consists of a small amount of required computer resources. In fact, the evaluation of the objective functions can be performed only for a limited set of sample points. This way, the recently proposed expensive criteria, based on the analysis of non-primitive flow variables, can be effectively implemented. The same for a multi-objective criteria, such as that one of Hunt et al., according to which the pressure field has to be minimized and the second invariant of the velocity gradient has to be maximized at the same time. Moreover, the present technique directly provides the position and strength of detected vortical structures. |
| S. R. N. De Zilwa, J. H. Uhm and J. H. Whitelaw. | VISUALISATION OF FLAMES STABILISED ON A PLANE EXPANSION. | chemi-luminescence, CH radical, combustion, oscillations. | The combustion of premixed methane and air downstream of a plane sudden expansion with velocities less than 13 m/s and over a range of equivalence ratios from around 0.85 to 1.15 gave rise to discrete frequency oscillations. The rms of the associated pressure fluctuations was less than 0.3 kPa and the dominant frequency varied from around 150 to 180 Hz with inlet velocities from 7 to 11 m/s. These oscillations were visualised in terms of the chemi-luminescence emission of the CH radical and results showed that they were characterised by periodic roll-up, growth and convection of combusting vortices. At equivalence ratios that did not give rise to these discrete-frequency oscillations, combustion was characterised by vortex pairing and the pressure spectra consisted of relatively broadband peaks with amplitudes of less than 0.1 kPa. The vortex pairing mechanism was eliminated by imposed pressure oscillations. |
| Di Cicca, G. M., Onorato, M., Iuso, G., Spazzini, P. G., Zurlo, N. | QUANTITATIVE FLOW VISUALIZATION OF A MANIPULATED TURBULENT BOUNDARY LAYER FLOW. | particle image velocimetry, vortex generator jets. | The development of the flow field produced by Vortex Generator Jets (VGJ) has been the subject of many studies, whose aim was the control of flow separation in adverse pressure gradient flows. Recently Schoppa and Hussain [Physics of Fluid, 1998], using DNS data of turbulent channel flows, demonstrated that spanwise integrated skin friction reduction may be obtained by counter rotating streamwise vortices. They showed that this technique may break the boundary layer vortex regeneration cycle by disrupting the unstable low speed wall streaks generated by previous or pre-existing streamwise vortices. With reference to these new developments, Digital Particle Image Velocimetry has been applied to the study of the flow turbulence of a flat plate boundary layer, "manipulated" by embedded streamwise large scale vortices produced by VGJ. Images in planes normal to the free stream, parallel to the wall and normal to the wall in the direction of the undisturbed mean velocity were analyzed to obtain mean and turbulent velocity profiles. The manipulated flow results were compared to the natural boundary layer ones. |
| G. E. Erickson. | EFFECTS OF PASSIVE POROSITY ON INTERACTING VORTEX FLOWS AT SUPERSONIC SPEEDS. | pressure-sensitive paint, laser vapor screen, Schlieren, vortex flows, supersonic speeds, shock wave. | Optical methods featuring pressure-sensitive paint, laser vapor screen, and Schlieren systems were applied to determine the effects of passive surface porosity on the interacting vortex flows about a general research fighter configuration at supersonic speeds. The quantitative and qualitative on- and off-surface flow visualizations are correlated with data obtained using electronic pressure-scanning and six-component internal strain gage balance instrumentation. The challenges associated with combining optical methods with the more conventional pressure and force/moment measurements are also discussed. |
| P. V. Farrell. | TWO-PHASE FLOW VISUALIZATION FOR FUEL SPRAYS. | fuel injection, two-phase flows. | Two-phase flows, particularly liquid sprays, provide a wealth of information when examined using flow visualization techniques. In this paper, we will present some of our recent results of qualitative and quantitative flow visualization for sprays. While the primary focus of this work is fuel sprays for internal combustion engines, the range of spray characteristics is broad including relatively low pressure sprays (3-8 MPa) and high pressure sprays (200 MPa) into a variety of environments. |
| S. Fonov, S. Mihailov, A. Morosov and E. Schairer. | DYNAMIC COMPENSATION OF THE PRESSURE FIELDS OBTAINED BY PSP METHODS. | pressure sensitive paint, pressure field visualization. | The response time of a pressure sensitive paint (PSP) active layer is determined by an oxygen diffusion process and is a function of the squared PSP layer thickness. The response time can be reduced to a minimum of around several milliseconds for a "fast paint" formulation that will correspond to "cutoff " frequency response of the PSP layer at about one hundred Hz. Thus, for investigation of transient pressure fields it is necessary to compensate the dynamic behavior of the PSP. The paper presents the methodology of evaluation of the PSP response time field and corresponding PSP image-processing scheme. Experimental results obtained on an oscillating model (M=0.45, F=0, 5, 10, 20 Hz) are used for demonstration of the data evaluation of flow processes. Comparisons with CFD results and estimation of the residual errors are presented and discussed. |
| Abdul Ghani S. A. A., Aroussi A and Rice E. | OPTIMISATION OF A PURPOSE BUILT AUTOMOTIVE CLIMATIC WIND TUNNEL USING COMPUTATIONAL FLUID DYNAMICS. | numerical simulation, climatic wind tunnel, car heating and ventilation. | This paper describes the design process of a closed loop full-scale vehicle Climatic Wind Tunnel. The aim is to design a climatic wind tunnel mostly to simulate a travelling vehicle subjected to the combined effects of different rainfalls and wind conditions. This will facilitate a close investigation into rainwater ingress into car Heating Ventilation and Air Conditioning system (HVAC). With the aid of Computational Fluid Dynamics (CFD) as a design tool, a detailed insight of the airflow characteristics of various tunnel parts is obtained. |
| V. Goriatchev. | THE RENDERING OF VECTOR FIELDS FOR VISUALIZING OF FLOWS IN COMPLICATED 3D CASES. | numerical prediction, flow vector fields, rendering. | A new approach to visualizing of three-dimensional vector fields after computer simulation is described. The final rendering in complicated cases of flow topology in 3D cavities, rotated channels and annuli is supported by combination of different types of streamlines and probe particle paths animation. The streamribbons and streamtubes are made more explicit by color rendering pigmentation along their surfaces according to the preliminary selected local streamwise characteristics of flows. The problems of accurate representation of vortex flows a using cloud of particles are discussed. |
| S. Gumkowski, M. Wierzbowski, J. Stasiek. | VISUALIZATION OF HEAT TRANSFER FROM AN OBLIQUE IMPINGING JETS ON FLAT PLATE USING LIQUID CRYSTAL THERMOGRAPHY. | liquid crystal, oblique jet, thermography | Experiments are conducted to determine the heat transfer to/from a jet impinging at different oblique angles to a plane surface liquid crystal coated on a mylar sheet used to locate isotherms on a flat plate. The color images associated with water jet, air-water spray and air jet are recorded by JVC-camera and true-color image processing developed by Data Translation Ltd. Studies of heat transfer from jets an oblique angle to a surface are relatively rare. Knowledge of spray and jet cooling/heating and interaction between the heat transfer and environmental conditions are of great practical importance. Therefore adequate and proper design of the impinging jet system is not a critical concern to mill designers and process engineers. In this paper a new procedure has been developed (this involves a false color scale representation of the local contours of local Nusselt number) to obtain the most important information about cooling/heating information, heat transfer coefficients (local and average) heat fluxes etc. |
| J. W. Hoyt and R. H. J. Sellin. | VISUALIZATION OF WATER FLOW OVER SAND DUNES. | cavity flow, tracer methods | The
formation of, and the complex flow over, underwater sand dunes is a problem
of practical importance, dealing as it does with sediment transport, channel
resistance, and large-scale turbulent structures in the flow. The fluctuating
flows which transport sediment and create dune movement have been difficult
to visualize using conventional dye tracers. A turbulent-flow dye tracer has been employed to illustrate some of the complex features found in water flow over a series of simulated sand dunes. The tracer is a mixture of a shear-thickening surfactant and a high extensional-viscosity polymer, exuded from a hypodermic tube into a region near the surface of a simulated sand dune. The simulated sand dune was formed from polystyrene foam, and installed in a small water channel at the University of Bristol. The 3 in-line dunes had a wave length of 0.568 m and a step height of 0.093 m. The average water velocity at the peak of the dunes was varied from 0.25 to 0.34 m/sec. Photos and video of the channel experiment show strongly recirculating flow in the dune cavity. An initial separated vortex can be seen. The "reattachment" location where the tracer strikes the opposite dune surface can be clearly seen. Tracer escaping the initial dune cavity repeats the excursions in the second and third cavities, but the tracer has mainly broken up and diffused by then. The ability of the tracer to remain coherent over much of this strongly turbulent cavity flow aids greatly in the understanding of these complex interactions. |
| Klaus Huenecke & Caren Huenecke. | FLOWFIELD VISUALIZATION IN AIRCRAFT WAKE VORTEX RESEARCH. | aircraft wakes, flowfield visualization. | Wakes from large
aircraft are characterized by immense rotating air masses. Aircraft encountering
such wakes, in particular when flying in rail on a densely flown approach
path, may experience severe control problems which in the past have lead
to numerous incidents and also to some accidents. As air traffic continues to grow and very large high-capacity aircraft are to enter service within the next five years, this invisible hazard to flight safety has alerted the aviation community and aircraft manufacturers, in particular. The wake issue has become a target for intensive industrial research efforts. The most prominent tool available for research is the large wind tunnel which allows wake lengths of some wing spans behind an aircraft model to be investigated in great detail. The method of pointwise scanning the flowfield at various streamwise positions behind the model leads to vast amounts of data which require efficient processing to extract the information contained in the data. The most important method is that of visualizing the flowfield. The investigations carried out by DASA Airbus cover a wide range of existing and future transport aircraft. An efficient visualization methodology had to be developed in order get insight into a highly complex flowfield and to handle large quantities of flowfield data. It was found convenient that various levels of visualization had to be applied for analyzing the data efficiently. Low-level visualization is typically marked by velocity arrow fields and flat shading representations of the flowfield in the surveying plane. This simple method is relatively fast and used for quick-look purposes in the wind tunnel, for example. The method is not well suited for detailed analysis of the flow, however, but may serve as a basis for such analysis. Intermediate-level visualization gives a much greater insight into flowfield details. The flowfield is typically represented by a carpet plot which requires greater effort to process the data, but also computer hardware capable of building-up the picture quick enough. Flat shading representations, on the other hand, may be upgraded to the intermediate level by adding pseudo streamlines in the measurement plane and by spatial velocity vectors indicating the magnitude of the streamwise flow component. Intermediate and low-level visualization may be combined to enhance perception of flowfield details. High-level visualization comprises complex representations of the flowfield. A typical example is a perspective view of a complete line-up of low-level representations, together with spatial streamlines and the generating aircraft itself. Also in this class are video sequences which allow fast motions within the flowfield to be studied which still pictures cannot provide. A requirement for this form of visualization is the availability of a large number of low-level visualization pictures which in turn requires software capable of calculating the flowfield in sufficient detail between measured planes. Examples will be given for all forms of visualization mentioned. |
| Koichi Ichimiya and Yoshio Yamada. | THE VISUALIZATION OF THREE-DIMENSIONAL HEAT TRANSFER AND FLOW BEHAVIOR ON A CIRCULAR IMPINGING JET. | impinging jet, liquid crystal, numerical calculation | This paper describes the heat transfer, flow characteristics and visualization on a single circular laminar impinging jet in a comparatively narrow space with confined wall. Temperature distribution and velocity vectors in the space were obtained numerically by solving three-dimensional governing equations. Local heat flux on the impingement surface was visualized by using thermosensitive liquid crystal. The meant Nusselt number was related to the Reynolds number and the space between nozzle and impingement surface. |
| Itoh, H., Honji, H. and Boyer, D. L. | SECONDARY STREAMINGS IN ROTATING OSCILLATORY FLOW OVER TOPOGRAPHY. | secondary streaming, oscillatory flow, flow visualization, topographic effect, Lorentz force. | A flow visualization study has been made of topographic effects in a quasi-2D oscillatory primary flow. This flow of an aqueous solution of sodium carbonate is driven at the centre of an initially flat-bottomed shallow tank by an electromagnetic Lorentz force that changes its direction left and right at constant period. The tracer particle method has been used to visualize surface flows. A steady secondary streaming, consisting of the four counter-rotating vortices symmetrical about the left-right axis of the primary flow oscillation, is always formed at the centre of the tank. When a square-cross-sectional straight groove is made in the bottom floor of the tank with its axis normal to the direction of the primary flow oscillation, the groove has been found to act as a bottom topography which produces a still-symmetric peculiar secondary streaming. In this streaming, some tracer particles move straight along the edges of the groove. When the background rotation is furthermore introduced by using a turn-table equipment, the symmetry of the four vortices on the groove is broken substantially. Cyclonic vortices are likely to be dominant while the anti-cyclonic ones disappear. The results may be of help in modelling such geophysical flows as the streamings over a canyon and other coastal topographies. |
| G. Jagadeesh, T. Mizukaki and K. Takayama. | MICRO-SHOCK WAVE VISUALIZATION USING HOLOGRAPHY. | micro-shockwave, holographic interferometry. | Using double pulse holographic interferometry, micro-shock waves are visualized. The micro-shock waves are generated using pulsed laser focusing. |
| G. Jagadeesh, K. Nagashetty, B. R. Srinivasa Rao and K. P. J. Reddy. | SEPARATED HYPERSONIC FLOW VISUALIZATION USING ELECTRIC DISCHARGE. | flow separation, hypersonic flow, electric discharge. | This paper describes an innovative method of visualizing separated hypersonic flows, using electric discharge. Flow separation on 120 degree. apex angle blunt cone flying at Mach number 5.75 has been visualized using electric discharge in the IISc hypersonic shock tunnel HST-1. Surface heat transfer measurements are carried out to verify the visualized flow separation. |
| M. C. Jermy, C. Santos-Nunez, P. Le Gal, N. Farrugia and D. A. Greenhalgh | SPRAY CHARACTERISATION INCLUDING DROPSIZE MEASUREMENT BY PLANAR LASER IMAGING. | sprays, dropsize, LIF, laser, volume fraction, fuel injection, fluorescence. | In the absence of turnkey two phase flow CFD codes, the measurement of sprays is vital for the design of liquid fuelled combustors of all types, coating, pharmaceutical and agrochemical delivery systems, and spray drying systems. Techniques such as Phase Doppler Anemometry and Fraunhofer diffraction allow the measurement of droplet size, concentration and velocity, characterising the spray effectively, but are slow and give poor spatial resolution. Imaging techniques are being developed to provide both full information and high resolution, as well as rapid mapping. The Laser Sheet Dropsizing technique, which uses the droplet diameter dependance of elastic and fluorescent light scattering to give droplet size and liquid volume fraction over a plane in the spray illuminated by laser and imaged by CCD camera, is one such technique. Because the technique relies on simple and robust properties of the scattered light, it can operate in dense sprays for which multiple scattering and multiple occupancy of the probe volume prohibit the use of other techniques. In addition unsteady processes can be rapidly probed throughout their cycle. Results are presented showing validation of the technique in a variety of industrial sprays. |
| Jae Won KIM. | FLOWS AROUND CROSS FLOW FAN IN ROOM AIR CONDITIONER. | cross flow fan, piv, air conditioning. | The flows in a cross flow fan (CFF) were observed by light scattering particles and measured by planar PIV system. CFF is widely used as an air movement unit in room air conditioning, air curtain system of showcase-refrigerator etc. In this work, the problem model contained CFF and related structures of a room air-conditioner such as a stabilizer. A wind-tunnel, constructed under ASHRAE rules, was prepared for measurement of inlet and outgoing velocity of CFF, in particular to study swirling flows inside the CFF. Also the tunnel had a few holes for measurement of pressure and controllable nozzles in the stream-wise direction. With this apparatus, the performance of the fan was be confirmed. The adopted PIV system depicted velocity field before, inside and after the CFF. The flow patterns near the suction and blowing side were close to predictions by many prior works. The main interest lies on the rotating flow inside the circumference blades of CFF. It was found that the swirling flow caused decreasing flow rate and unwanted noise. However, the vortex motion was adjusted by changing the shape of a stabilizer. Practically, an improved unit of CFF and solid structure is found by this research. Also the present results supply comprehensive design data for new model of room air conditioner. Consequently, a series of experiments dealing with flows related to a solid inlet optimal geometry for a silent performance and enriched flow rate were conducted. |
| V. Kornilov, S. Nikiforov and A. Pavlov. | A MODIFICATION OF GISF METER UTILIZING DIFFUSE LIGHT SCATTERING. | GISF, diffuse light. | A
novel modification of the GISF (Global Interferometer Skin-Friction Meter)
technique is described. Unlike the conventional GISF method this modification
utilizes a diffuse light scattering to register fringe patterns, which allows
the measurement of skin-friction on curved and free-oriented surfaces. The
tests were conducted in a subsonic wind tunnel where an airfoil with a relative
thickness equal to 0.07 was investigated at the incidents of 0 and 5 degrees.
The free-stream velocity was equal to 25 m/s corresponding to the Reynolds
number, based on the airfoil chord, of 428000. The results obtained show a good agreement with the same obtained by means of other techniques as applied to well known airflows. For some types of airflow the GISF technique provides more accurate results in comparison with the methods based on the similarity theory. |
| H. H. Korst, R.A. White, and C. Kunze. | MODELING AND VISUALIZATION OF COMPRESSIBLE NON-STEADY GAS FLOWS IN PIPES. | visualization, gas flow, pipes. | Non-steady one-dimensional
flows have a wide range of applicability, for instance in automotive intake/exhaust
systems, the transmission of finite amplitude waves in pneumatic control
systems and the operation of pulsating propulsion and combustion devices.
For a long time, the analytical investigations have been based on the graphical
treatment by the method of characteristics, but the availability of high-speed
digital computers has led to the more efficient utilization of numerical
analysis, in particular the inverse marching Euler (implicit) predictor/corrector
method . Strictly one-dimensional flows have thus been treated successfully
under wide ranges of initial and boundary condition and compared with experimental
data obtained for transient wave systems in shock tubes. In addition, it
has been found that use of the water analogy (water table) has allowed the
qualitative and quantitative visualization of analytically predicted results. Extensions of strictly one-dimensional flow configurations to include changes in duct cross sections and directions (elbows) are here the subject of attention. The analytical treatment of such problems is accomplished by the introduction of singularities generating interactions in the form of wave reflections and modified transmissions. The upstream and downstream effects are then compared with experimental data obtained in shock tubes and observed on the water analog. In particular, the events cover non-steady, one-dimensional gas flows in pipe systems of different geometry, such as (a) changes in pipe cross sections, (b) changes of flow directions, such as elbows (c) boundary conditions ( open, closed ends, pistons at the end, and nonlinear elements, such as reed valves) all for different initial conditions. |
| Kulenovic R., Mertz, R. and Groll, M. | HIGH SPEED VIDEO FLOW VISUALIZATION AND DIGITAL IMAGE PROCESSING OF POOL BOILING FROM ENHANCED TUBULAR HEAT TRANSFER SURFACES. | pool boiling, enhanced heat transfer, flow visualization, high speed video,digital image processing. | In the frame
of a R&D project (sponsored by the Commission of the European Communities,
JOULE programme) the heat transfer characteristics of novel tubular heat
transfer surfaces operated in the pool boiling mode under saturation conditions
(fluid propane) are experimentally investigated. The major objective is
to improve the heat transfer from enhanced heat transfer surfaces, especially
for low and medium heat fluxes (<100 kW/square meter), which shall be used
in future industrial compact heat exchangers. The experimental work comprises the determination of the heat transfer coefficient (thermocouple measurements). Flow visualization experiments are also carried out using a high speed video system and digital image processing for data evaluation. The parameters of interest are the bubble departure diameter, the frequency of bubble generation and the flow velocity field. These parameters are employed in numerical models and in empirical correlations to predict the heat transfer performance of the enhanced heat transfer surfaces. The paper describes in detail the experimental set-up and the employed measurement and evaluation techniques. The results of the experimental investigation are shown as heat transfer coefficients vs. heat fluxes. The visualization results are both qualitatively and quantitatively presented and the quantitative results of the digital evaluation of the high speed video data are discussed. |
| V. Kulish | TWO PHASE FLOW THROUGH BIFURCATING AIR PASSAGES OF THE HUMAN RESPIRATORY SYSTEM. | CFD, two phase flow, respiratory system, fractals. | Presence
of solid particles in the air flow through air passages of the respiratory
system influences the gas exchange process in lungs and is often a cause
for different respiratory and cardiovascular diseases. Two phase flow through air passages of the human respiratory system has been simulated for the all 23 bifurcational generations by means of CFD with application of fractal modeling of the duct geometry and description of the flow as a diffusion-like process in the constructed fractal space. The result of the simulation allows to trace and describe the behavior of solid particles toward their appearance in the alveolar region, where they start influencing the gas diffusion process |
| R. Kwong, K. Lam and R. M. C. So. | INVESTIGATION OF IN-LINE CIRCULAR CYLINDERS IN A CROSS-FLOW USING PIV AND LIF. | in-line cylinders, LIF, PIV, full-field flow measurement. | It is of great importance in tube-bundle, chimneystack and bridge abutment designs to obtain some quantitative and qualitative information on a series of cylinder that arranged in-line relative to the free-stream. Previous investigations showed that even with the same diameter and identical pitch, the interstitial flows might vary drastically in the near wake. Particle image velocimetry (PIV) was used to observe the instantaneous velocity field in these investigations. A high-speed PIV system has been developed to gain understand of the near-wake patterns, the flow separation and the full-field velocity distributions among the cylinders. Laser-induced fluorescence (LIF) technique was used in conjunction with PIV in order to gain better insight into the complex flow around in-line cylinders. |
| LEE, Young-Ho, Im Yu-Cheong, Choi Jang-Woon. | PIV APPLICATION TO THE OPTIMUM DESIGN OF INDUSTRIAL PUMPS | PIV, industrial pump, design, high-speed. | PIV measurements of flow associated with industrial pumps was carried out with the aim of optimising design. A hardware system based upon an image intensifier, gated, CCD Camera was adopted to give a maximum time resolution of 30 micro seconds. Transparent visualization windows were used to obtain clear flow images in the experimental region. A grey-level, cross-correlation algorithm capable of minimized uncertainties in flow estimation was developed and applied to acquire accurate velocity components at high operating flow speed. Application of the system, to a diffuser pump and small boiler-water circulating volute pump, gave useful, detailed instantaneous and time-mean flow information which again was used in design for improved performance. |
| LEE Young-Ho, SEO Min-Sik, CHOI Jang-Woon. | A NEW 3-D PIV ALGORITHM AND ITS APPLICATION. | PIV, 3-D, algorithm. | A new algorithm for full 3-D PIV is suggested based on the application of the DLT (Direct Linear Transformation) method to solve the identification of the same particles discretized in separate stereo CCD image planes. Uncertainty is minimized mathematically and performance comparisons are made by applying the method to standard Internet 3-D images. More realistic application with higher accuracy will be presented in the final paper. |
| Li, H., Bunnel, R., Collicott, S. H., and Heister, S. D. | INTERNAL FLOW VISUALIZATION AND CFD IN HIGH-PRESSURE DIESEL FUEL INJECTORS. | imaging, cavitation, CFD. | Emission requirements
drive the design of modern diesel fuel injectors to operating pressures
of approximately 2000 atmospheres. Because of structural damage to the
orifices, cavitation of the fuel at the entrance to the injector orifices
has long been known to occur. Yet little research in such flows exists.
Scaling of unsteady cavitating flows in impossible, so true pressure and
scale experiments are necessary. The extreme pressure and the small size
(approximately 200 microns diameter) of this internal flow create a true
challenge for both flow visualization and computation. Flow visualization and CFD results of the unsteady two-phase low inside of true-scale diesel injector holes as small as 200 microns diameter and at pressures up to 2000 atmospheres are presented. True three-dimensional geometry effects including hole tilt and inlet cross-flow are included. Implications of the results and relative strengths of experiment and CFD are discussed. |
| Chang Lin and Peng-Hao Chiu. | FLOW CHARACTERISTICS OF HORSESHOE VORTEX AT A VERTICAL PLATE - FLAT PLATE JUNCTURE. | holography, shock waves, solid/liquid interfaces | The
boundary layer on the wall ahead of a bluff body is in a region of adverse
pressure gradient, and within some distance upstream of the body this boundary
layer experiences a three-dimensional separation. In the separated region,
a system of vortices is developed and stretched around the base of the body
like a horseshoe shape. Cases of such three-dimensional problems occur frequently
in many engineering practices. For example, cooling flow past computer chips
on a circuit board, flows around wing-fuselage and turbine blade-hub junctions,
and local scouring round the base of a bridge pier. In this paper the characteristics of laminar horseshoe vortex system near the juncture of a vertical plate (with finite transverse length) and a flat plate were investigated experimentally, using particle image velocimetry (PIV), fiber laser Doppler velocimetry (FLDV), and particle tracking flow visualization technique. Several important parameters which may influence the flow structures of laminar horseshoe vortex system are the aspect ratio of the vertical plate, the Reynolds number of approaching flow, and relative height of the laminar boundary layer. The purpose of the present study is to provide the most comprehensive classification and description of the range of horseshoe vortex system. Moreover, the characteristics of the steady type and regular type are pointed out in the present study. Several detailed flow structures in the steady type, regarding the position of primary vortex core, down-flow velocity profile, the circulation of primary vortex, and the position of stagnation point on the model will be discussed. The range of the Reynolds number Re, based upon the free stream velocity and the width of vertical plate, is from 400 to 1200. |
| T.-M. Liou and C. C. Chen. | LIQUID CRYSTAL MEASUREMENTS OF HEAT TRANSFER IN A ROTATING, 180-DEG, SHARP TURNING DUCT. | liquid crystal, heat transfer, sharp turn, rotation. | Flow visualization using a transient liquid crystal method was used to study the effect of rotation on the local heat transfer distributions around a sharp 180-deg turn of a two-pass, smooth, square duct. Detailed local Nusselt number distributions on the leading and trailing walls are given for rotation number, Ro, ranging from 0.01 to 0.2 at a Reynolds number of 10000. The results show that, in the first pass, rotation decreases on the leading wall while heat transfer rate decreases on the trailing wall. In the turn, heat transfer rate increases greatly on the leading wall, and moderately on the trailing wall with increasing Ro. In the second pass, heat transfer is enhanced greatly on the leading wall with increasing Ro while enhanced slightly on the trailing wall. Moreover, the heat transfer distribution map derived from the study, including detailed spanwise variation, gives an insight into the flow characteristics in a rotating channel. |
| T. Maxworthy. | THE EFFECT OF A STABILIZING GRADIENT ON INTERFACE MORPHOLOGY. | interface/frontal instability; non-linear morphology; stabilizing gradients. | Sedimenting and
combustion fronts, immiscible fronts in journal bearings and printing rollers,
wine-tears, interfaces in tapered Hele Shaw cells, in the peeling of flexible
tape, in directional solidification, etc., all exhibit a similar morphology
in their non linear instability characteristics. These similarities appear
to be forced by a gradient in one of the external, controlling parameters.
Visualisations, the physical basis and the underlying dynamics of each of
these systems will be presented in some detail.
|
| N. P. Migoun, P. P. Prokhorenko, S. G. Chizh. | FLOW VISUALIZATION IN "POROUS LAYER-CAPILLARY" SYSTEMS. | fluorescence, dye visualization, liquid penetrant testing. | The widely used liquid penetrant testing (PT) is a reliable, high-sensitive non-destructive method to detect surface discontinuities. Every PT process consists of some technological stages including two the most important ones. The first one is the filling of defect's hollow with a penetrant (dye or fluorescent liquid). During the second stage the developer (usually porous layer) acts to draw out penetrant entrapments from deep down in cracks to the test surface where they can be seen. It was established some years ago that such a model of surface defect as one-side conical capillary, being immersed in some liquids, can be filled both from the channel's entrance (classical liquid column) and from its closed top, which have no direct connection with penetrating liquid. Recently new experimental and theoretical results were obtained and compared. It was shown satisfactory correspondence between experimental results and theoretical model of film flow in conical one-side-closed capillary. The effectiveness of penetrant testing strongly depends on particularities of drawing out of a penetrant from defects by developer's layer. Basic principles of hydrodynamic model of this process for dry developer were proposed in our paper. This theory enable to determine some practically important characteristics of PT process. Capillary pressures both in defect's channel and in porous layer, which govern interrelated flows in a defect-developer system, represent crucial forces of development process. Theoretical model corresponds experimental results in many practical cases, but our recent researches shows that sometimes one more physical mechanism of defect's development exists. We developed the set-up for flow visualization during the process of liquid penetration into the developer layer from one-side closed capillary. The intriguing result was as follows. In certain cases an air bubble appears in the region of capillary outlet and cuts off a direct connection between liquid column and a developer. In spite of this fact the liquid is extracting from a capillary (preliminary filled with a penetrant) into porous layer. We suggest that the physical mechanism of such kind of development can be explained in the frame of the same theoretical model of film flow, based on the concept of disjoining pressure, as in the case of conical one-side-closed capillary. Some experimental results of our investigation are presented in the paper. |
| B.E. Milton, R.D. Archer nd M. Burgess. | DETAILS OF THE BREAK-UP AND ENTRAINMENT PROCESSES INTO AIRSTREAMS OF LIQUID WALL DROPLETS. | shadowgraph, shock waves, droplets. | In a previous study of liquid wall droplet entrainment into airstreams using shock wave to provide the required air velocity, shadowgraph photographs normal to the flow direction were used. These provided substantial information on the time dependent entrainment sequence but many aspects of the distorting droplet structure remained obscure. As the droplet shape, wave build-up and atomisation from the upper crests are very repeatable, a new technique has been developed. Here, three identical runs are carried out in sequence. These consist of a normal shadowgraph and two angled photographs at 45degrees front and rear of the droplet. The latter use a high intensity flash, Macro zoom lens and ASA 400 film. The structure of the droplet during the entrainment process is now clear. A cave-like structure develops in a form somewhat like a Gothic arch with atomised micro-drops being shed from the crest at its apex. The droplet bulk migrates along the duct floor leaving a thin sub-layer spreading both directly behind and outwards to either side. The liquid in this region is only entrained into the flow by evaporation. The quantity of liquid in the varying regions is being quantified. |
| Mokry, M., Xu, H. and Yeung, A.F.K | EXPERIMENTAL AND NUMERICAL VISUALIZATION OF WING TRAILING VORTICES. | piv, numerical flow visualization. | The paper describes three different visualization techniques applied to the study of wing trailing vortices at the Institute for Aerospace Research in Ottawa. The particle image velocimetry is applied to a half-wing test in the 9m x 9m Low Speed Wind Tunnel. Examples of the visualization of the vortex formation by a pulsed laser, quantified by cross-correlation of the smoke particles, are given. The flow field around a flapped wing is also simulated numerically, using the Navier-Stokes solver of the WIND code. The separate C-grid topologies of the wing and flap, generated by the ICEM MULCAD software, are coupled using the chimera overlapping grid strategy. Vortex-specific physical phenomena, such as the initial rollup at wing tips and sub-vortex orbiting, are observed using the animated motion of fluid particles. Finally, simple vortex particle and vortex sheet methods are employed to visualize the development of the vortices and their interactions with atmospheric and ground shear layers. Presented are live computer simulations, showing the birth of secondary vortices and their interactive motion in crosswind. Based on these observations, the prospects of real-time wake vortex warning systems are discussed. |
| S. Nikiforov and A. Pavlov. | THE USE OF FIELD INTERFEROMETERS FOR PANORAMIC LDA. | panoramic LDA, field interferometers, velocity field registration. | The velocity fields registration by traditional LDA methods requires sequential scanning of the examined flow and is possible only for stationary or sufficiently reproducible flows. A method for panoramic velocity measurement with the use of field interferometers that allows not only the velocity fields measurement, but also their visualization is described. The method is based on direct optical registration of the Doppler frequency shift and has no upper limit restrictions imposed by the measured velocities. The lower limit is determined by the actually available dimensions of the interferometer and is approximately 70 m/s per fringe with the length of the interferometer equal to 1 m. This corresponds to an accuracy of 7 m/s, if the fringe pattern is resolved with the accuracy equal to 0.1 of the fringe. The output information is a fringe pattern of finite fringes. The volume of registered information is considerably reduced (by orders of magnitude, compared with the PIV method), processing algorithms become more simple and spatial resolution is determined mostly by the quality of the used optical devices. The test performed show the feasibility and prospects of the method for panoramic velocity measurements, especially at high velocities (100 m/s and higher) when the PIV methods often prove problematic to use. |
| M. Novak, B. Sirok and F. Trdic. | THE MEASUREMENT OF TIME FLUCTUATION OF BLUFF BODY VORTEX STREET WITH AID OF DIGITAL IMAGE-PROCESSING TECHNIQUES. | bluff body, computer-aided visualization, power spectra, scalar patterns, vortex shedding. | The measurement of the time fluctuations of vortex structures in a vortex street behind a bluff body using digital image-processing technique is described. A two-dimensional image of the vortex street behind the prismatic bluff body in the wind tunnel was visualized with aid of a high-speed camera. The level of grey intensity in images obtained in this way provide scalar patterns, varying in space and time, which can be observed using computer-aided visualization. By successive digitization of the grey intensity distribution images these areas, simultaneous time series were generated. Power spectra describing a distribution of vortex structures in the bluff body wake were calculated. Results indicate that significant frequencies occur in the bluff body wake according to vortex shedding theory. The transition from recurrent behaviour, periodic or quasi-periodic, to non-periodic behaviour is represented by a change from a spectrum with dominant frequencies to one without such features. |
| H. Ohue, G. Kawashima, and Wen-Jei Yang | RAYLEIGH-TAYLOR FLOW INDUCED BY A ROTATING HEATED CIRCULAR SURFACE. | natural convection, rotating circular heated surface, thermal pattern, liquid crystal suspension, laser lightsheet. | An experimental study is carried out to investigate the Rayleigh-Taylor flow induced by a combined action of natural convective and rotational forces over a rotating heated circular surface. The test system consists of a concentric unheated outer cylinder and a heated inner cylinder which are enclosed by two side walls. Its rotating axis is set horizontally. Distilled water and glycerin water solutions of different concentrations are employed as test liquids. Rotating speed and heating rate are varied. A temperature-sensitive liquid crystal suspension is used as the tracer with the flow field illuminated by a laser light sheet. Flow and thermal fields resulting from a combined action of natural convective and rotational forces are governed by the Rayleigh and Taylor numbers. It is disclosed that: (i) after the thermal field reaches a quasi-steady state, thermal patterns can be classified into six kinds, including thermal stratification, lean thermal stratification, thermal entrainment, wheel spoke, circular saw teeth, and circular form. They vary depending on the rotational speed, liquid viscosity, heating rate and spacing or radius ration of the concentric cylinders: (ii) These thermal patterns can be correlated by the Rayleigh number versus Taylor number. Hence, it is justifiable to name it "Rayleigh-Taylor" flow. |
| R. H. Page, Seyed-Yagoobi, and V. Narayanan. | AIR FLOW VISUALIZATION VIA INFRARED THERMOGRAPHY. | infrared, thermography, jet . | A new technique for visualizing complex air flow fields utilizing heated sulfur hexaflouride is described. Examples of its use with unique impingement jets of air are presented. Infrared thermography is used to visualize the traces of sulfur hexaflouride in the air. |
| S.A.Pavlov and A.S.Petrosyan. | THE NEW METHODOLOGY FOR CLOUD TOP FLOW VISUALIZATION FROM SATELLITE DATA. | cloud visualization, satellite, cyclones | The
main objective of the suggested work is to improve predictions of cloud
top entrainment phenomena based on satellite data analyses. A new analysis
methodology for the cloud top 2D-flow reconstruction from remote sensing
data is developed and suggestions for further satellite missions and data
sets is discussed. Validation examples based on available data is provided.
The method uses a set of images of the cloud layer, with known temporal and spatial resolution, in order to obtain flow pattern. Visual movement and deformation of the picture are considered, as an atmospheric flow perturbation, and in the simplest situation considered identical. The algorithm analyses pairs of consecutive monochromic images, in a particular spectral range, removes deformation from the image field and measures translation between the images. Cloud free regions are identified and their velocity field calculated. This technique is limited by the time resolution of input data, so there are some restrictions for experiments methods. In the analysis of cyclones in the Earth's atmosphere, with the scale about thousand kilometers, a temporal resolution of some minutes is required, while at the present time the resolution available is about one hour depending on satellite orbit. Possible development to pairs of stereo images allowing vertical cloud movement is discussed. |
| W. D. Peters and J. E. S. Venart. | ROUGH-SURFACE GRAVITY CURRENT FLOWS. | laser-induced fluorescence, gravity currents, rough surfaces. | An accidental
release of a large quantity of flammable gas from a railcar accident, for
instance, can have detrimental consequences due to the explosive nature
of the product. If the gas instantly ignites at the time of the release,
a large explosive fireball can rapidly expand away from the scene causing
death and destruction in its path. If no immediate ignition occurs, however,
a gas cloud will accumulate in the region of the accident scene with the
potential for later ignition. In this situation, emergency response officials
need to predict the movement of the cloud to minimize the risk to surrounding
people, structures and environment. If the flammable gas is normally lighter than the surrounding air, it will quickly rise and, typically, dissipate in the atmosphere without incident. However, a heavier gas cloud, such as formed by propane, will slump to the ground and spread horizontally away from the source with the lay of the land, risking further damage to people and areas remote from the accident scene. Influenced primarily by the effects of gravity, this dispersion flow phenomena is known as a gravity current. The downstream ignition and/or explosion potential of this heavier-than-air-gas (HTAG) cloud is greatly diminished as it mixes with the surrounding air so that its concentration is reduced. Terrain features such as buildings, trees, hills and other protuberances tend to enhance this mixing process, as confirmed by the present research, by enabling more air to be mixed into the cloud as the cloud passes over and around them. Consequently, flows over rougher terrain can lead to greatly reduced downstream distances at which the gas clouds no longer present a significant threat. Considerable past effort in this area has focused on the development of predictive computer simulations used to model the mixing and spreading behaviour of these clouds. However, many of these models are based on data gained from experiments involving large- scale gas releases over flat terrain or water and are not fully able to predict flows over more rough terrain as is commonly encountered. Also, although a large amount of gravity current flow research has been carried out over the years, there is a still a general lack of work being carried out to address the basic understanding of how this flow interacts with rough surfaces. Accordingly, small-scale experimental research was carried out to assess the effects of surface roughness on the downstream mixing and spreading of a gravity current flow. The experimental methods used combined the techniques of saltwater modelling, laser-induced fluorescence visualization and digital image processing. The research was carried out in three phases: 1) the development of the modelling, visualization and analysis techniques, 2) the validation of these techniques using published results for well-documented, smooth- surface flow studies and 3) the evaluation of how well the published smooth-surface flow theories extend to rough-surface flows so that an appropriate rough-surface model could be developed. Results of this work have provided a more complete understanding of how surface roughness facilitates the mixing mechanisms that occur between the HTAG cloud and the surrounding air during a dispersion. For instance, the uniqueness of the application of the laser-induced fluorescence visualization technique to the study of gravity currents has provided a significantly more detailed picture of the mixing within the flow. Using this method, two-dimensional planar concentration profiles of the gravity current structure were obtained which highlight the magnitude and location of the mixing mechanisms in the flow. As a result, it was recognized that a mixing mechanism, previously regarded in the literature as being insignificant for smooth-surface flows, has a very significant effect on mixing over rougher surfaces. Consequently, a rough-surface model was developed to account for this effect. It is hoped that the results of this research contribute to the on-going development and improvement of predictive models for HTAG dispersions. |
| E. Sabadini and R. C. R. Figueredo. | OPTICAL DENSITY IN THE STUDY OF FRAGMENTATION OF DILUTE POLYMER SOLUTIONS JETS. | drag reduction, jet flow, optical density, flow visualization. | Flow visualization
has been currently used in the study of polymer drag reduction. This work
presents an optical technique which allows to verify the effect of drag
reducers on the jet structure by flow visualization. Such technique consists
in the analysis of transmitted laser radiation through the jet flow, which
carries information about the flow patterns. Sequential images of the light patterns generated by the transmitted laser radiation are captured by a digital CCD camera, and then processed and treated graphically for obtaining the spatial distribution of intensity in the images. The turbulence degree and the presence of poly(ethylene oxide), PEO, molecules lead to remarkable changes in the optical density profile and in the intensity of the pattern formed by the transmitted radiation. Such changes are related to the oscillation amplitude and to the jet flow fragmentation. The established methodology has demonstrated that the intensity distribution of the transmitted radiation depends on flow nature. Furthermore, the contrast and dynamics exhibited by the images of the dilute PEO solution jets show that the presence of PEO in the range of 60 to 200 ppm alters significatively the jet structure. |
| E. Sabadini and M. I. Alkschbirs. | DRAG REDUCTION STUDIED BY SPLASHING VISUALIZATION. | splash, drag reduction, visualization. | The splash, in
the present context, is a phenomenon which happens on droplet impact against
a shallow liquid surface (target), forming a structure called crown. After
the collapse of the crown, a liquid column (Rayleigh jet) arise on the surface.
Splashing has been studied from a great variety of viewpoints, in different
fields such as agronomy, biology, engineering, astronomy, photography and
marketing. The visualization of the splash was used, in the present case,
to study the drag reduction effect that happens when very low concentrations
of a high molecular weight polymer are present in the fluid under investigation. A controlled drop-releasing device was developed, fitted with a high-speed CCD camera [with shutter speed of (1/10000)s], and an image acquisition and processing system. With this assembly, it was possible to observe large changes in the splash structures of water, especially in the extension of the Rayleigh jet. This result was associated with the drag reduction effect produced by the polymer. Results obtained with the dyed drop technique showed that the presence of the polymer affected the relative contributions of the drop and the target to the structure of the crown. |
| E. Sabadini and E. Teixeira Neto. | THE INFLUENCE OF POLY(ETHYLENE OXIDE) ON THE VORTEX BREAKDOWN STUDIED BY FLOW VISUALIZATION. | vortex breakdown, visualization. | Complex flow structures may result when the fluid inside in a cylindrical container is submitted to rotation of one end wall. These structures are similar to “bubbles” of recirculation. The phenomenon, termed as “vortex breakdown”, is sensitive to variations in the geometric parameters of the container, namely height of fluid column/diameter, end wall angular velocity and the physical-chemical properties of the fluid. In the flow process the fluid swirls along the the cylindrical wall and subsequently in the axial direction. For some conditions, the vortex undergoes a stagnation and complex structures are produced. Due to the high sensitivity of the vortex breakdown, a study has been made of the influence in the phenomenon, produced by low amounts of dissolved poly(ethylene oxide), PEO. The images of the flow were obtained using a CCD camera (30 frames/s). The flow was visualized by using dye (methylene blue) dissolved in the fluid. The fluid was composed by a mixture of glycerin (60%) and water (40%). The main morphological parameters used in the study were the stagnation point and the width of the flow structure. Large changes in these parameter were observed using PEO concentrations lower than 40ppm. These results showed that the vortex breakdown was a very sensitive technique to study polymer reology. |
| G. Sargsyan, R. Yessayan and I. Vardanyan. | MODELING OF COOL FLAME COMBUSTION FLOW CONDITIONS OF GAS MIXTURES. | cool flame, combustion, gas mixtures, flow conditions. | The importance
of using visualization in combustion processes of organic compounds is in
the determination of the formation of the products of the reaction. The
registration of their radiation from these products in an excited state
allows a determination of the establishment of the oscillatory, dynamic
modes, and the optimization and the stabilization of combustion processes
in various devices. The modeling of combustion processes allows the investigation
of mechanisms of the complex processes, the role of the separate elementary
acts, feedback and relaxation phenomena. In this work on an example of acetaldehyde oxidation, the model involving surface processes and feedback (inhibition), has been considered. The leading, active centers of chain process - peroxy radicals (RCO3) produce on the surface of the reaction vessel an inhibitor - are highly vibrationally excited molecules of formaldehyde (CH2O (v)). Depending on the life-time of the exited products of heterogeneous recombination of radicals, the oscillations processes can be located at different distances from the wall of the reaction vessel. This will be influence the character of the luminescence of the exited particles and thickness of the luminous zone at a wall of a reaction vessel. The case of the formation of highly-vibrationally-exited molecules of inhibitor, which can penetrate to a large distance distance from a wall. It is shown that the relaxation rate does not influence remarkably on the size of this zone. The perimetric analysis has shown, that depending on magnitude of parameter describing the relaxation rate of exited molecules, a wide range in values of both frequency and size, amplitude and duration of oscillations in the system. |
| E. Savory, N. Toy, S. Okamoto and Y. Mitsutami. | VORTEX DOMINATED FLOWS WITHIN SUBSONIC 3-D CAVITIES. | cavity flow, thymol blue, laser Doppler anemometry. | The subsonic flows associated with rectangular planform cavities set within an otherwise plane surface are of interest in many different areas, from vehicle aerodynamics to river channel hydraulics. The flow within the cavity is dominated by large-scale vortical motions which become increasingly complex as the incidence angle changes from a direction which is normal to the main cavity axis. For such yawed configurations the vorticity is highly three-dimensional in nature, such that the flow behaviour is not yet fully understood. The present paper concerns a flow visualization study using models in a water channel. The visualization is by the thymol blue tracer technique which permits the evolution of the vortical flows through entrainment of the tracer over time, without the intrusion of a probe into the flow. The image sequences are supplemented by data from a related study of the flows within cavities where the mean velocities and turbulence distributions have been obtained within a wind tunnel cavity model using laser Doppler anemometry. |
| S. Seitanis and P. Anagnostopoulos. | NUMERICAL VISUALIZATION OF CROSS-FLOW PAST TWO STAGGERED ROWS OF CYLINDERS. | cylinder rows, streamlines, vorticity contours. | The
objective of this study is the numerical solution of cross-flow past two
staggered rows of cylinders, at different downstream displacements. The
downstream row comprised four cylinders and the upstream row three cylinders.
For a fixed Reynolds number the flow field and the hydrodynamic forces are
greatly dependent on the distance between adjacent cylinders of the same
row, and on the displacement between the rows in the streamwise direction.
The phenomena are potentially very hazardous, because the hydrodynamic forces
associated with the flow field may induce vibrations on the tubes, with
destructive effects for the whole arrangement. In the present investigation
the finite element technique was favored for the solution, for Reynolds
numbers ranging between 100 and 1000. The stream function, vorticity, pressure
and the hydrodynamic forces on the cylinders were calculated at each time
level. The computation was continued, until the flow field was fully established.
Then, in order to investigate the effect of the cylinder oscillation on
the flow pattern, the upstream row was excited sinusoidally in the streamwise
direction, in a way that all the tubes of the row move in unison. Various
oscillation amplitudes were tested, up to 50% of a cylinder diameter. From the nodal values of the stream function and vorticity the streamlines and vorticity contours throughout the flow field were generated, while the nodal values of pressure yielded the isobars. The numerical visualization technique provides a complete description of the flow pattern. The comparison of the flow field and of the associated hydrodynamic forces between the static and dynamic case when the in-line displacement of the rows is the same, is very important for the understanding of the potentially hazardous effect of the cylinder motion. |
| I. Semenova and G. Dreiden. | HOLOGRAPHIC INTERFEROMETRY OF WAVE PROCESSES IN FINITE SOLIDS AND AT SOLID/LIQUID INTERFACES. | holography, shock waves, solid/liquid interfaces. | The paper presents research on the laser induced shock wave propagation through a liquid/solid interface, its succeeding evolution in a solid waveguide and interaction with the next solid/liquid or solid/solid interface. These processes have been studied in regard to the research on the possibility of the strain solitary wave formation in a solid waveguide. We present observations of some nonlinear phenomena appearing both in the wave interaction with an interface and in its evolution in the waveguide. Waves under study were recorded by means of the technique of holographic interferometry which allows to visualize the whole process and to obtain the complete set of data at different stages of the wave evolution. |
| G. Settles et al. | VISUALIZING THE AERODYNAMICS OF CANINE OLFACTION. | canines, schlieren, scattering, particulates, high-speed video. | The global landmine problem has recently reached unprecedented proportions. Despite an array of proposed high-tech detection schemes, trained canines out-perform all other forms of landmine detection. They do this by olfactory sensing of a trace explosive signal associated with a buried mine. Yet, dogs are expensive to train and have short attention spans. Efforts are under way to develop "electronic dog's nose" which can be used reliably in the field. A variety of disciplines must come together effectively in order for this to succeed. Not the least of these technologies is "aerodynamic sampling". Research being conducted at the Penn State Gas Dynamics Lab aims at gaining an understanding of the aerodynamics of the olfaction process through a series of flow visualization experiments. |
| G. Settles et al. | APPLICATIONS OF FULL-SCALE SCHLIEREN IMAGING. | Schlieren, focusing, wide-field, HVAC, shock waves, ventilation, leak detection. | Since the construction of the Penn Stat, Full-Scale, Schlieren system in the 1990's (Settles et al., Proc. ISFV7), a variety of visualizations of full-scale airflows has been performed. These include kitchen ventilation, room cooling by displacement ventilation, leak detection, shock wave visualization, and the imaging of the human thermal plume as part of an effort to develop an explosives detection security portal. These and future applications will be illustrated and reviewed. |
| B. W. Skews. | OBLIQUE IMAGING FOR VISUALIZATION OF 3-D NON-AXISYMMETRIC SUPERSONIC FLOWS. | supersonic flow, shock wave reflection, oblique imaging. | The wave interaction geometry for two supersonic bodies in close proximity can become very complex. Conventional imaging with the optical system axis perpendicular to the tunnel window can lead to misinterpretations. Rotating the optical axis in roll, pitch, and yaw enables the position of various features to be established. Doing so dynamically produces animations which allow much clearer interpretation, and from which geometric models can be constructed using computer aided design (CAD). The technique is also used to clarify changing wave patterns which occur when there is relative movement between the bodies. |
| K. Takayama. | THREE-DIMENSIONAL VISUALIZATION OF SHOCK WAVE PHENOMENA. | holographic interferometry, three-dimensional shock waves, shock reflection, unsteady flow. | Using diffusive object beams three-dimensional shock waves were successfully visualized by double exposure holographic interferometry. Its techniques and examples will be presented in detail. |
| J. Tanny and J. Cohen. | VELOCITY FIELD MEASUREMENTS OF A DOUBLE-DIFFUSIVE TWO-LAYER SYSTEM IN A LATERALLY HEATED ENCLOSURE. | double diffusion, piv, stability | An experimental study was carried out to investigate the velocity field of a two-layer, salt-stratified fluid in a laterally heated enclosure. Due to the lateral heating of the enclosure, a circulating flow was induced in each layer such that the interface separating the layers was simultaneously exposed to destabilizing shear and double diffusive convection. The main goal of this work was to measure the velocity field and to correlate it with the behavior of the two-layer system. The experiments were carried out in a box with inner dimensions of 10 x 10 x 10 cm. Two sidewalls of the box were made of stainless steel and served as heat exchangers, and the two other sidewalls were made of optical glass to facilitate flow visualization. The velocity field was measured using the PIV (Particle Image Velocimetry) method. The velocity fields obtained showed that under unstable conditions rows of moving vortices existed above and below the interface. On the other hand, when the interfacial flow was stable, no vortices were observed. |
| N. Toy, P. J. Disimile and E. Savory. | THE FLOW REGIME IN 3-D RECTANGULAR CAVITIES WITHIN A SUPERSONIC BOUNDARY LAYER USING LIQUID CRYSTALS. | liquid crystals, cavity flow, supersonic. | The effect of the flow regime within 3-d rectangular cavities immersed in a turbulent boundary layer and subjected to a freestream Mach number of 2 has been studied using liquid crystals. The planform of the cavities (L/W) has ranged from 4:1, 6:1, 8:1 and 12:1 for the same width to depth ratio (W/D). This series of experiments has concentrated on the observation of the complex flow regime as the cavity is yawed to the freestream flow. It will be shown in the full paper that the liquid crystals may provide shear stress distributions on the cavity floor for all geometries and assist in explaining the mechanism that is taking place as the cavities are yawed. It will be shown that for planform ratios less than about 6:1 the cavity behaves like a closed cavity throughout the range of yaw angles, but as the planform ratio increases, the cavity flow changes from the closed to open condition as the cavity is yawed from 0 to 90 deg. |
| Toya, Y. and Nakamura, I. | A WAVE MOTION ON THE FREE SURFACE OF THE TAYLOR VORTEX FLOW WITH AN ASYMMETRIC SYSTEM. | fluid dynamics, Taylor vortex flow, wave motion, free surface, chaos. | This study clarifies the feature of the wave motion of the free surface of the flow between concentric rotating cylinders, where the inner cylinder is rotating and the outer one is stationary. The characteristic flow on the free surface develops from Couette flow to the outside ring-shaped flow, to the flow with a wave motion and to the complicated wave motion flow finally with increasing Reynolds number. This experimental investigation clarifies the behavior of the wave motion of free surface by a visualization technique and shows the variation of the height of the surface by a supersonic sensor with the Reynolds number. The variations of the level of the surface are analyzed with FFT and the features of the surface as a function of the Reynolds number is discussed. This development of free surface between cylinders is concerned with the mixing and the diffusion for fluids and also is considered using chaos theory. |
| P. X. Tran. | FORMATION AND DEVELOPMENT OF A LASER IGNITION KERNEL. | high speed digital video, laser spark ignition, ignition kernel, detonation, flame propagation. | The high speed digital video camera is used in the study of single and multi-point laser spark ignition of CH4-air mixtures in a constant-volume cell. The tests are carried out using two Q-switched Nd-Yag lasers lasing either at 1064 or 532 nm. Firing of the lasers was controlled by a digital delay/pulse generator. Two modes of firing are used: sequential firing, and simultaneously firing. The camera is configured to record the formation and temporal development of the ignition kernel, detonation wave velocities, and flame propagation speeds. |
| S. Umeda and Wen-Jei Yang | COMPARISON OF WAKE FLOWS BEHIND SQUARE AND CIRCULAR CYLINDERS. | singular square and circular cylinders, flow visualization, LDV, wake flow characteristics | Our previous study revealed the occurrence of flip-flop phenomenon in the exit streams from diamond-shaped cylinder bundles which has never been observed in circular cylinder bundles. This motivates us to investigate the basic difference in wake flows behind single square (a special diamond-shaped quadruple) and circular cylinders. Two kinds of experiments are performed: flow visualization and two-dimensional laser Doppler velocimetry (LDV). The former yields flow patterns by means of fluorescent dye injection illuminated by a laser light sheet. The LDV produces velocity vector distribution, and one can use the results from this to calculate the distributions of vorticity, turbulence intensity, and Reynolds stress. It is disclosed that: (i) flow variation in the vicinity of the shear layer (the border between the main flow and wake flow) is greater for the square cylinder case than the circular cylinder case at lower Reynolds numbers, as evidenced by the appearance of more longitudinal vortices. As the Reynolds number increases, longitudinal vortices appear more clearly and flow oscillations become more visible in the wake flow regions of both types of cylinders: (ii) at any Reynolds number, the square cylinder has a wider wake-flow region than the circular cylinder. However, the width diminishes with an increase in the Reynolds number: (iii) at lower Reynolds numbers, the wake-flow region of the square cylinder is characterized by stronger vorticity, turbulent intensity, and Reynolds stress than that of the circular cylinder, with the difference diminishing with the Reynolds number. It is believed that these differences serve as a source of disturbance to trigger a hula (Polynesian dance) movement of an attached vortex over the downstream apex of the quadrilateral cylinder in diamond-shaped cylinder bundles, in which exit streams exhibit a flow-flow oscillating phenomenon. |
| S. Umeda and Wen-Jei Yang. | A LASER DOPPLER VELOCIMETRY STUDY OF FLOW AT THE INTERSECTION OF CONVERGING DUCTS AND DIVERGING DUCTS. | flow characteristics, converging-diverging streams, flow intersecting region, shear layer, LDV. | There are studies of flow in a converging-diverging duct such as a Venturi flow, and flow in two intersecting ducts called a flow network. Both flow systems are basic to fluid mechanics and have important engineering applications. The present study deals with flow in a system that combines the two: a pair of converging ducts (at a converging angle Alpha1) connected to a pair of diverging ducts (with a diverging angle, Alpha2). A flow network is formed when Alpha1 and Alpha2 are equal, while a Venturi flow results when both Alapha1 and Alpha2 are reduced to zero. Flow and its oscillatory behavior in the intersecting region of the converging-diverging duct pairs are investigated by means of laser Doppler velocimetry (LDV). Both the converging and diverging angles are varied, is the flow rate through the intersecting region. Velocity vector and power spectrum distributions are obtained from the LDV measurement, from which the distributions of vorticity, Reynolds stress and lateral and longitudinal turbulence intensity are calculated. A finding of importance concerns velocity variation along the shear layer in the intersecting region. It exhibits a peak velocity located downstream from the midpoint of the shear layer. This signifies that the total kinetic energy resulting from the collision of two converging streams, which occurs between the converging point (intersection of the inner surfaces of the two converging ducts) and the peak, is dissipated over the range between the peak and the diverging point (the intersection of the inner surfaces of the two diverging ducts). This phenomenon explains the mechanism of convective heat transfer performance in a flow network. The observation is further corroborated by the power spectrum distribution. |
| F. T. Van Der Laan and V. C. Ferreira. | HIGH VELOCITY MEASUREMENT IN FLUIDS USING "PIV" TECHNIQUE AND INTERLACED IMAGE PROCESSING. | flow visualization, particle image velocimetry. | Measuring high velocity in fluid flows is not an easy task. Processing image techniques, such as particle image velocimetry (PIV), with continuous laser sheet and conventional CCD cameras, operating at 30 frames per second, allows good measurement, only for slow flows. For a faster flow, this technique, unfortunately, is not suitable. But at present time, a new generation of digital CCD-DV cameras, with controlled shutter velocity, is been introduced in the marked. This new feature turned possible measure velocities up to 100 m/s, even without pulsating the laser light. This work shows a technique for processing frames captured at different shutter velocity and recorded into a digital DVT (digital videotape). One image of double field (even and odd fields) is captured and the processing is done between both fields. An image, captured with variable shutter velocity (ranging from 1/30 up to 1/10000 seconds), is recorded onto a DVT to be, digitized by an interface board into a microcomputer and processed, afterwards. The processing algorithm is based on a cross correlation and autocorrelation technique between both fields and a post-processing procedure presents the flow field results. |
| Michael Vloeberghs and F. Daemi. | VIRTUAL REALITY MODELING OF THE HUMAN VENTRICULAR SYSTEM. | nmr, ciss,human brain, virtual reality. | A virtual reality model of the human ventricular system was created based on Nuclear Magnetic Resonance (NMR) data. A CISS sequence was used to define the boundaries between the Cerebro Spinal Fluid (CSF) and the surrounding tissue eg. brain and arachnoid. An automated routine was produced that reconstructs the ventricles and allows rendering in virtual reality. This modeling technique is being used in a research project regarding the physiology of the ventricular system. |
| Russell V. Westphal, Robert A. Kennelly Jr.and A. Drake. | SKIN FRICTION FOOTPRINT OF THE VORTEX/BOUNDARY LAYER INTERACTION. | skin friction, oil film interferometry, vortex, boundary layer. | The skin friction footprints of vortex/boundary layer interactions occurring in several aerodynamic flows are compared using oil film interferometry. The vortices for each case are created by small "generators" and are relatively weak, so that they create slowly-evolving, weakly three-dimensional flows. The oil film interferograms allow rapid, low-cost visual and quantitative characterization of the resulting skin friction distributions. For example, the interferograms for a single streamwise vortex interacting with an incompressible turbulent flat plate boundary layer display a skin friction peak-and-valley pair corresponding the the vortex downwash and upwash of boundary layer fluid. Other cases presented include a transonic vortex/boundary layer interaction on a swept wing model and a vortex pair/boundary layer interaction on an aircraft wing in flight. |
| M. Wierzbowski, M. Ciofalo and J. Stasiek. | INVESTIGATION OF FLOW AND HEAT TRANSFER IN A FINE-TUBE HEAT EXCHANGER ELEMENT. | heat transfer, numerical prediction, thermochromic crystals. | The use of thermochromic liquid crystal technique and true-colour image processing system in heat transfer modeling is described. Experimental procedure cover full-field flow patterns in classic heat exchanger elements (flat plate with fine-tubes in-line, staggered and with vortex generators) describing local heat transfer coefficient and Nusselt number on the surfaces. Also the dependence of average heat transfer and pressure drop on Reynolds number and geometrical parameters was investigated. Numerical prediction is proceeded using flow modeling software. |
| H. Yamada,T. Naitoh,K. Nakajima,T. Utsumi,T. Katoh,Y. Sumiya. | EXPERIMENT ON PULSATING JET EJECTED FROM CIRCULAR NOZZLE. | pulsating jet, vortex ring, puff, smoke visualization. | This paper describes some specific features and the classification of pulsating jets. The flow fields and the motions of vortices characterizing the pulsating jets were experimentally examined using both the smoke visualization method and velocity measurements obtained by hot-wire anemometer. The results of the velocity variation are found to agree with those of the flow visualization. The pulsating jets can be classified into three kinds of flow state; they are termed a row of puffs, a row of vortex rings in jet column mode, and a row of vortex rings in shear layer mode. In this paper, we defined the puff as a lump of fluid consisting of a leading vortex and a trailing jet following the vortex. The puff may be regarded as the state possessing the most fundamental features of a pulsating jet. Each run corresponds to a point on a 2-D regime, where the governing parameters are chosen as the coordinate variables. The plotted result of the points indicates that the choice of the parameters is adequate to classify the flow states. |
| Wen-Jei Yang, S. Torii and S. Umeda. | FLUID-FLUID INTERACTION IN FLOW NETWORKS. | flow networks, visualization, flow and thermal characteristics, experimental and theoretical methods. | A flow network
is a system of mutually intersecting holes inside a plate or an assembly
of plates. The flow at each intersection is characterized by a collision
of two flow streams, resulting in complex flow patterns through the downstream
holes. In the case of multiple intersections, the flow is periodically disrupted
at each succeeding intersection, thus preventing the formation of a fully-developed
flow through the holes. Hence, it is expected that a flow network provides
a better mixing of flows, and consequently, a higher heat-transfer performance.
This article employs both experimental and theoretical methods to investigate fluid-fluid interactions in flow networks consisting of either single or multiple pairs of intersecting channels. The methods include the tracer method assisted by a laser light sheet string method, laser Doppler velocimetry, piezometry, a numerical method, and prototype testing. Various unique phenomena are discovered, some of which are uncommon or nonexistent in other flow and thermal systems. Examples include ramming effects, maximum kinetic energy point, centrifugal effect, Coanda effect, flow separation region, flip-flow stream oscillation, optimal frequency of power spectrum. Results contribute to broadening basic knowledge in flow mechanics and heat transfer. |
| Yu, M., Wang, X., Wang, D., and Li, D. | APPLICATION OF PTV SYSTEM TO FLOW FIELD MEASUREMENT IN LARGE-SCALE PHYSICAL MODELS | ptv, piv, flow field measurement. | It is of great importance to measure the instantaneous velocity field in physical models of river engineering. Particle Tracking Velocimetry (PTV) technique was adopted in the measurement of large-scale physical models. A fast PTV system, suitable for measurement of both steady and unsteady flows, was developed in this paper. This system with one PC and six CCD cameras covers an area of about 120 sq metres and the area increases with the increase of the number of computers and cameras. Generally, the minimum time span between two successive measurements is 20 seconds. Thus, continuous and automatic measurement can be realized. The system has been applied to several models with steady and reliable results. |
| G. Zharkova, A. Dovgal, V. Kovrizhina and Yu Zanin. | INVESTIGATION OF FLOW SEPARATION ON A FINITE SPAN WING BY LIQUID CRYSTAL COATINGS. | three dimensional flows, finite-span wing, liquid crystal, thermography. | An
aerodynamic problem of wing operation is boundary layer separation which
may have a very significant effect upon lift, drag and local flow characteristics.
Extensive studies are being carried out in order to develop reliable methods
for prediction and control of the phenomenon. As a result, some of fundamental
features of separated flows have been recognised by fairly simple 2D models
which have been elaborated. However, flow physics in separation regions
is more complex than it can be expected from the 2D approximation. The 2D
approximation does not take into account the three-dimensionality inherent
to separated flows. Separated flow structures in an incompressible fluid is the topic of present paper. The aim of experiments is the examination of surface flow patterns on a low aspect ratio wing and the varying basic aerodynamic parameters. The method used for this purpose is visualisation by liquid-crystal (LC) coatings and true-colour image processing. As a result, systematic variation of the 3D surface flow pattern with Reynolds number and angle of attack was obtained. |