Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
12
2
2005
NUMERICAL VISUALIZATION OF UNSTEADY VORTEX SHEDDING
105-110
Giancarlo
Alfonsi
Fluid Dynamics Laboratory, Universita della Calabria, Via P. Bucci 42b, 87036 Rende (Cosenza), Italy
The flow generated by a viscous incompressible fluid past an impulsively started circular cylinder at the Reynolds number 1000 (based on free-stream velocity and the cylinder diameter) is visually described for several time steps of integration by means of computer generated images of the vorticity field. The flow-field representations are based on the results of a computational code in which a mixed spectral-finite analytic technique is used for the numerical integration of the two-dimensional time-dependent Navier-Stokes equations. The mutual interaction of the primary vortices in the near wake of the cylindrical body, as a fundamental mechanism of the vortex shedding phenomenon, is demonstrated.
VISUALIZATION OF UNSTEADY FLOW PHENOMENA OF WELLS TURBINE DURING HYSTERESIS STUDY
111-123
M.
Mamun
Department of Mechanical Engineering, Saga University, 1, Honjo, Saga, 840-8502, Japan
Toshiaki
Setoguchi
Institute of Ocean Energy (IOES), Saga University, 1, Honjo-machi, Saga 840-8502, Japan
Y.
Kinoue
Department of Mechanical Engineering, Saga University, 1, Honjo, Saga, 840-8502, Japan
K.
Kaneko
Department of Mechanical Engineering, Saga University, 1, Honjo, Saga, 840-8502, Japan
To visualize the flow field around the blade of the Wells turbine during hysteresis, experimental and numerical investigations were made including deep stall condition of the Wells turbine. The experimental investigation was made using a turbine-equipment with a simulated sinusoidal flow condition. The numerical investigation was made by an unsteady three-dimensional Navier-Stokes numerical simulation. A counterclockwise hysteretic loop is observed in unstalled condition, which can be associated with a streamwise vortical flow appearing near the blade suction surface. Besides, a clockwise hysteretic loop is observed in deep stall condition, the flow structure of which can be considered similar to that of the dynamic stall of an airfoil.
FOURIER ANALYSIS OF THE SPECKLE-PHOTOGRAPHIC, DENSITY-SENSITIVE FLOW VISUALIZATION METHOD AND APPLICATION OF THE "SHARP-FOCUSING" EFFECT
125-136
Axel
Hanenkamp
Lehrstuhl fur Stromungslehre, Universitat Essen, D-45117 Essen, Germany
Wolfgang
Merzkirch
Universitaet Duisburg-Essen
Schwarzwaldstr. 18, 79102 Freiburg, Germany
The speckle-photographic method that has become an attractive alternative to traditional optical flow visualization methods is described and modeled by means of the Fourier analysis. The speckle displacement due to the presence of a flow with varying fluid density is verified with numerical simulation in the case studied. The speckle displacement as the signal is a measure of the refractive light deflection, similar to the information obtainable with a schlieren system; but the analysis visualizes the principal differences between the physical effects used for schlieren and speckle measurements. In order to avoid the shortcomings of this "line-of-sight" method in resolving three-dimensional test objects, an attempt is made to combine the speckle technique with the "sharp-focusing" effect known from schlieren technology. Preliminary experiments with a flow of known density distribution demonstrate that the implementation of "sharp-focusing" can deliver spatially resolved results.
INFLUENCE DUE TO ARRANGEMENT OF SPLITTER PLATE ON FLOW PAST A CIRCULAR CYLINDER
137-149
S.
Vengadesan
Fluid Mechanics Laboratory, Department of Applied Mechanics, Indian Institute of Technology
Madras, Chennai, Tamil Nadu, India
600036
B.H.Lakshmana
Gowda
BTL Institute of Technology, Department of Mechanical Engineering, Bommasandra, Bengaluru - 560 099, India
Flow visualization studies on the effect of placing a short splitter plate in the wake of a circular cylinder are reported. The splitter plate of ID length, where D is diameter of the cylinder, is placed both along the axis line and eccentrically behind the cylinder. From this study, the critical gap distances for different eccentric distances are found. When the plate is kept at eccentric distance of 1.3D from the cylinder axis, no influence is observed at all.
SIMULTANEOUS VISUALIZATION OF WAKES AND INTERNAL WAVES GENERATED BY TOWED CYLINDERS IN STRATIFIED FLUIDS
151-174
H.-T.
Liu
StereoVision Engineering, 14765 SE 56th Street, Bellevue, WA 98006
Thin fluorescent dye layers were deposited in a stably stratified towing tank to visualize both the wake and internal-wave fields generated by horizontally towed cylinders. The wakes consist of laminar, vortex, and tubulent regimes, depending on the Reynolds number RD or an empirical stability parameter a which takes into account the effects of stratification. Internal waves generated by the towed cylinders and the laminar wakes are steady and stationary to the cylinder-fixed coordinates except for localized flows inside rotors formed at very low Froude numbers. Unsteady internal waves generated by vortex and turbulent wakes are two- and three-dimensional, respectively. Qualitative and quantitative information derived from the visual experiments is applied to characterize the generation and evolution of steady and unsteady internal waves.
REAL GAS EFFECT ON TRANSIENT FLOW PHENOMENA IN A REFLECTION SHOCK TUNNEL
175-195
Jr-Ming
Miao
Department of Materials Engineering, National PingTung University of Science & Technology, Shuefu Road, Neipu, Pingtung, Taiwan.
Chun-Chi
Li
Chung Cheng Institute of Technology, National Defense University
Fuh-Lin
Lih
Center of General Education, R. O. C. Military Academy, Kaohsiung, Taiwan, R.O.C. and School of Defense Science Studies, Chung Cheng Institute of Technology, National Defense University, Taoyuan, Taiwan 335, R.O.C
This study numerically analyzes transient multi-shock flow phenomena in a full-reflection shock tunnel using CFD. Based on the finite volume method, the compressible Navier-Stokes equations are solved with the upwind Roe's scheme and the total variation diminishing (TVD) scheme. To consider the real gas effect, the polynomial correlations of Tannehill and Mugge are applied to modify the equation of state in simulating the hypersonic environment. For either a perfect or viscous flow with the real gas effect, the flow features of the shock train, reflected shock wave/boundary layer interaction in the shock tube, and the Mach reflection configuration in startup process of nozzle flow are clearly observed in this work. The effect of the half-nozzle angle on the startup process of nozzle flow is also explored. The flow establishment time from placing a spherical model in the test section is 8.0 ms, and the effective flow test time is 3.5 ms.