Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
7
1
2000
VISUALIZATION OF FLOW THROUGH A CASCADE OF ELLIPTICAL CYLINDERS
8
10.1615/JFlowVisImageProc.v7.i1.10
J. W.
Hoyt
Department of Mechanical Engineering, San Diego State University, San Diego, California, USA
R. H. J.
Sellin
Department of Civil Engineering, University of Bristol, Bristol, U.K.
A coherent tracer method of flow visualization has been used to investigate the complex flow patterns produced by a bank of elliptical cylinders. These visualizations are used to help explain earlier heat transfer measurements on a similar cascade of elliptical cylinders. The cylinder geometry comprised a row of four elliptical elements having major axes aligned at 0, 30, 60, and 90° to the main flow, with varied spacing between the cylinders. The elements themselves were 2.63 to 1 elliptical shapes, with 0.073 m major axes.
The cascade flow was visualized in a small glass-sided water channel at the University of Bristol, using tracer streams composed of a mixture of shear-thickening and high extensional-viscosity components (Hoyt & Sellin [1]). This tracer resists breakup and dispersion in highly turbulent flows, such as those encountered in cascades. The Reynolds number of the individual elements of the cascade (based on the major axis) ranged from 15,200 to 16,500.
NUMERICAL VISUALIZATION OF THERMAL FLOW STRUCTURE AND CONCENTRATION CONTOURS IN METAL ORGANIC CHEMICAL VAPOR DEPOSITION REACTORS
12
10.1615/JFlowVisImageProc.v7.i1.20
C. Y.
Soong
Rotating Fluids and Vortex Dynamics Lab, Department of Aeronautical Engineering, Chung Cheng Institute of Technology, Tahsi, Taoyuan, Taiwan 33509, ROC
R. Y.
Tzong
Research and Development Department, EVEREST Technology Corporation, Hsinchu Industrial Park, Huko, Hsinchu, Taiwan 30300, ROC
The present work is concerned with the numerical visualization of flow patterns, temperature fields, and concentration contours in a low-pressure metal organic chemical vapor deposition (MOCVD) reactor with a rotating susceptor. For simulation of the variable-property gas flow, the dilute mixture approach is invoked, and the compression work and thermal diffusion effects are also included. By considering gas inlet pressures of 0.2, 0.1, and 0.05 atm at various rotating rates, the influences of the operating pressure on the flow fields and the epitaxial growth rate are examined. The central theme of the present work lies in visualizing the details of the flow fields at various operating conditions in order to diagnose the flow quality and attain profound physical insights into the mechanisms of macrotransport phenomena of large-area epitaxy in low-pressure MOCVD reactors.
A TEMPLATE MATCHING-BASED METHOD FOR IDENTIFYING THE SEPARATION POINT OF BUOYANT WALL JETS
10
10.1615/JFlowVisImageProc.v7.i1.30
Cristian
Ghiaus
LEPTAB — Laboratoire d'Etudes des Phenomenes de Transfert Appliques au Batiment, Universite de La Rochelle France; Technical University of Civil Engineering, Bucharest, Romania
Amina
Meslem
LaSIE, University of La Rochelle Pole Sciences et Technologie La Rochelle, France
K.
Abed-Meraim
LEPTAB — Laboratoire d'Etudes des Phenomenes de Transfert Appliques au Batiment, Universite de La Rochelle France
M.
Robitu
LEPTAB — Laboratoire d'Etudes des Phenomenes de Transfert Appliques au Batiment, Universite de La Rochelle France; Technical University of Civil Engineering, Bucharest, Romania
A cold air jet introduced just below a horizontal wall attaches to the wall and then separates from it. The distance between the separation point and the inlet nozzle is an important design parameter for air conditioning systems. Using laser-light sheet visualization, the separation point can be located by either visual observation or image processing. Nevertheless, the unsteadiness of the separation point, induced by the turbulence of the jet, requires tens or hundreds of readings for one determination, making visual measurement tedious and hardly reproducible. As an alternative, the separation point of the jet from the wall may be numerically located where the highest correlation between the image of the jet edges and the template representing the characteristic separation pattern is found in the image. The correlation, calculated using the Discrete Fourier Transform, also gives a measure of the separation point location clarity.
STROBED LASER-SHEET VISUALIZATION OF A HELICOPTER ROTOR WAKE
20
10.1615/JFlowVisImageProc.v7.i1.40
Preston B.
Martin
Department of Aerospace Engineering, Glenn L. Martin Institute of Technology, University of Maryland, College Park, Maryland 20742
Mahendra J.
Bhagwat
Department of Aerospace Engineering, Glenn L. Martin Institute of Technology, University of Maryland, College Park, Maryland 20742
J. Gordon
Leishman
Department of Aerospace Engineering, Glenn L. Martin Institute of Technology, University of Maryland, College Park, Maryland 20742
The individual wakes trailing behind each blade of a helicopter rotor form turbulent vortex sheets that quickly roll into concentrated tip vortex filaments. A phase-locked, strobed laser light-sheet illuminating a seeded flow has been shown to provide both a quantitative and qualitative method to study the evolution of this turbulent wake. The tip vortex cores can be identified by a well-defined seed void. The shear layer produced by the blade wake appears as a line of discontinuity in the streaklines. Because the vortex core is a rolled-up portion of the original trailed wake, the vortex core and the vortex sheet were studied as interdependent flow structures. Some outboard portions of the vortex sheet were found to descend axially through the flow at a greater rate than the tip vortex core. While maintaining some connection to the original vortex core, the vortex sheet interacts with the tip vortex trailed from another blade. During the interaction, three-component laser Doppler velocimetry (LDV) measurements show a substantial increase in the angular velocity of the fluid within the vortex core. A three-dimensional reconstruction of the wake geometry in terms of the core trajectories agrees with results measured by LDV.
DEVELOPMENT OF 3-DIMENSIONAL BLADE DESIGN SYSTEM USING VIRTUAL REALITY TECHNIQUE
12
10.1615/JFlowVisImageProc.v7.i1.50
Hiroyuki
Aoki
Graduate School of Mechanical Engineering, Science University of Tokyo, 1-3 Kagurazaka, Shinjuku-ku, Tokyo, 162-8601, Japan
Makoto
Yamamoto
Department of Mechanical Engineering, Tokyo University of Science, 6-3-1 Niijuku, Katsushika-ku, Tokyo, 125-8585, Japan
Conventional blade rows in turbo-machinery have been designed 2-dimensionally. However, the enhanced request to improve the performance makes 3-dimensional design inevitable. In the present study, we propose a design system for 3-dimensional blade, applying virtual reality techniques. Using a head mount display and a pen-type 3-D mouse, this system enables a designer to visualize the flow field and to modify the blade configuration. Once the shape of a blade is changed, the flow around the modified blade is calculated and the results are displayed on the head mount display, iteratively. IRIS Explorer is basically used for the flow visualization. The flow is assumed to be 3-dimensional, inviscid, and compressible because of the light computational load. This system would be effective in knowing the trend of aerodynamic performance with deforming a blade configuration, and is also promising for students and/or beginners in learning 3-dimensional flow fields around a 3-dimensional blade.
VISUALIZATION OF OSCILLATORY FLOW IN A BRANCHED TUBE
16
10.1615/JFlowVisImageProc.v7.i1.60
Akiyuki
Yonekawa
Department of Aeronautics and Astronautics, University of Tokyo, Tokyo, Japan
Toshinori
Watanabe
Department of Aeronautics and Astronautics, University of Tokyo, Tokyo 113-8656, Japan
Oscillatory water flows in a branched tube were visualized by tracer methods to obtain a fundamental view of the flow phenomena effective for the enhancement of gas exchange in the human lung system. From the results, longitudinal vortices were found in the branched region, which were well known as the secondary flow vortices in a curved flow channel. The longitudinal vortices were observed to interact with the flow separation at the branch position, and to cause strong mixing. The effect of the longitudinal vortices on mass transport in the flow was studied from the measurement of the local concentration of the mingled ink in water in a curved tube where a pair of longitudinal secondary vortex was generated. The results revealed that the effective diffusion coefficient in the curved tube was about 3.2 times larger than that in a straight tube for the studied case.
THERMAL FIELD AROUND A HORIZONTAL ISOTHERMAL CYLINDER WITH A LONGITUDINAL PLATE FIN
10
10.1615/JFlowVisImageProc.v7.i1.70
Shigeaki
Inada
Department of Mechanical System Engineering, Gunma University, 1-5-1 Tenjincho, Kiryu, 376-8515, Japan
Masahiro
Yamazaki
Department of Mechanical System Engineering, Gunma University, 1-5-1, Tenjincho, Kiryu, Gunma 376-8515 Japan
The natural convective thermal field in the air around a horizontal isothermal cylinder with a longitudinal plate fin is visualized by means of laser holographic interferometry. The cylinder is either heated or cooled to maintain a constant surface temperature, while either a copper (conducting) or a balsa (insulating) fin is attached longitudinally on the cylinder at various circumferential locations to grasp the effect of fin-air interaction on convective flow patterns that appear in the form of interference fringes. As a result, a vertically ascending (in the heated cylinder case) or descending (cooled case) plume interacts with an air stream along the fin. Subsequently, it is discovered that an optimal circumferential fin location exists at which local heat transfer performance around the cylinder becomes uniform. The optimal circumferential location is unaffected by fin material and is unchanged, always situated downstream of the plume irrespective of the cylinder being heated or cooled. An additional experiment is performed on frost formation on a cooled cylinder. It is found that a substantially more uniform thickness of frost is formed on the cylinder surface when a fin is attached on the optimal circumferential location than in the absence of a fin.