Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
15
4
2008
VORTICAL STRUCTURES ANALYSIS IN JET FLOWS USING A CLASSICAL 2D-PIV SYSTEM AND TIME RESOLVED VISUALIZATION IMAGE PROCESSING
275-300
10.1615/JFlowVisImageProc.v15.i4.10
Ilinca
Nastase
CAMBI Research Center, Technical University of Civil Engineering in Bucharest, Building Services Faculty, Avenue Pache Protopescu 66, Bucharest, Romania
Amina
Meslem
LaSIE, University of La Rochelle Pole Sciences et Technologie La Rochelle, France
Thierry
Bouwmans
Laboratoire Mathématiques, Images et Applications, University of La Rochelle, France
An optical field measurement technique and a high-speed visualization technique enriched by a low-level image processing are associated in the vortex dynamics analysis of the near field of jet flows. In a round jet the entrainment is produced in the braid regions being interrupted in the presence of the Kelvin-Helmholtz ring. The latter crush the streamwise vortices altering their self-induction role. Conversely, a lobed cross-shaped orifice geometry allows a cutting of the Kelvin-Helmholtz structures into discontinuous ring segments. Consequently, streamwise large-scale structures are developing in these discontinuity regions. The streamwise structures control and enhance the jet entrainment which is not altered by the Kelvin−Helmholtz structures passing.
OBSERVATION OF THERMALS IN MIXED CONVECTIVE GAS FLOW OVER A MODEL HEATED SUBSTRATE
301-312
10.1615/JFlowVisImageProc.v15.i4.20
Jyh-Long
Tuh
Department of Living Services Industry, Asia-Pacific Institute of Creativity Miaoli, Taiwan 35153, ROC
Experimental flow visualization has been carried out to investigate the characteristics of thermals and their relation to the evolution of longitudinal roll patterns in mixed convection of air over a circular heated plate mounted on the bottom of a horizontal flat duct. The results reveal that thermals with three different appearances are observed in the progression of end view flow photos, namely, the knotted thermals situated slightly beyond the onset point, the subsequent mushroom-shape thermals in the core region of the duct, and the deformed thermals located at each far side of lateral extension upon the heated plate. It is noted that on top of the heated surface, regular thermals arrange in unequal distance and lose their spanwise symmetry slightly. Moreover, the onset points of thermals all land on the circular heated disk and are in a shape of a concave downward curve in the flow direction. At higher buoyancy the generated knotted thermals unsteadily oscillate up and down and move spanwisely in the region slightly beyond the onset point which in turn results in meandering of the smoke streaks on top view accompanied by the bifurcation points of rising thermals to move back and forth in the axial direction. This explains the snaking motion proposed in the literature. Besides, coexistence and new generation of thermals are observed in the intermittent transition.
RECONSTRUCTION OF CURVED PARTICLE STREAK TRAJECTORIES
313-327
10.1615/JFlowVisImageProc.v15.i4.30
Marcus
Rosenstiel
Vision Systems E-2, Hamburg University of Technology, Harburger Schloßstr. 20, 21079 Hamburg
Rolf-Rainer
Grigat
Vision Systems E-2, Hamburg University of Technology, Harburger Schloßstr. 20, 21079 Hamburg
We present a method for reconstructing curved particle trajectories from particle streak velocimetry. The reflection properties of a particle are modeled as a point light source. The mapping of the particle on the image is spread by the point spread function of the camera lens. Therefore we can model the mapped particle trajectory as a convolution of the resting particle with its trajectory. Here we model the particle trajectory as a two-dimensional, symmetric Gaussian function convolved with a Bézier curve as an approximation of the trajectory with the pixel aperture of the camera. We assume that the velocity of the particle is constant over the measurement period. We will show that the particle trajectory can be reconstructed up to sub-pixel accuracy. This is verified with synthetic particle trajectories and qualitative comparisons with real world measurements.
KINETICS OF PITCHING SD8020, CH10SM, M06-13-128, AND NACA 2414 HYDROFOILS
329-336
10.1615/JFlowVisImageProc.v15.i4.40
Wei Ming
Tan
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50, Nanyang Avenue, Singapore, 639798
Wee Sern Vincent
Chai
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50, Nanyang Avenue, Singapore, 639798
Sutthiphong
Srigrarom
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50, Nanyang Avenue, Singapore, 639798
The purpose of this research is to investigate the flow field of pitching hydrofoils of different geometries in the water tunnel, and examine the corresponding forces and moments for pitching motion. This is to enable us to find the suitable hydrofoil geometry to be used for swimming or flapping applications. In order to understand how different hydrofoil geometries affect the various forces acting on it, experiments are conducted to study the hydrodynamic force and flow field around a pitching hydrofoil. In addition, the findings are enhanced by using the dye flow visualizations, PIV analyses, and the CFD simulation. The experiments are conducted on both the symmetrical and asymmetrical hydrofoils such as the symmetrical SD8020, and asymmetrical CH10SM, M06-13-128, and NACA 2414. Among the four hydrofoils investigated, we conclude that symmetrical SD8020 hydrofoil performs the best, followed by asymmetrical M06-13-128 hydrofoil, then asymmetrical CH10SM and NACA 2414 hydrofoils.
EXPERIMENTAL INVESTIGATION OF FLOW IN A BLADELESS ROTARY BLOOD PUMP USING PARTICLE IMAGE VELOCIMETRY
337-350
10.1615/JFlowVisImageProc.v15.i4.50
S.
Sastry
Department of Mechanical Engineering, Case Western Reserve University, Cleveland, Ohio, U.S.A.
Jaikrishnan R.
Kadambi
Department of Mechanical Engineering, Case Western Reserve University, Cleveland, Ohio, U.S.A.
John M.
Sankovic
National Aeronautics and Space Administration, John H. Glenn Research Center, Cleveland, Ohio, U.S.A.
M. P.
Wernet
National Aeronautics and Space Administration, John H. Glenn Research Center, Cleveland, Ohio, U.S.A.
V.
Izraelev
Advanced Bionics Inc., Hopkins, Minnesota, U.S.A.
Development of an efficient rotary blood pump depends upon understanding its flow characteristics. This investigation focuses on obtaining the flow characteristics of the pump using Particle Image Velocimetry (PIV). A three-disc optically clear magnetic drive bladeless pump is investigated. The refractive indices of the impeller, pump casing material and the blood simulant liquid are matched (1.485) to minimize the light scattering at the liquid−solid interfaces. The blood simulant fluid is composed of sodium iodide solution, glycerin, and distiller water. Neutrally buoyant solver coated hollow glass spheres are used as seed particles for PIV. Measurements are made at representative flow rates at which the pump will operate when used as a cardiac assist device. An average of 700−1000 image pairs are analyzed using the cross-correlation technique to obtain the flow field. An ensemble size of 700 data sets results in an uncertainty level of ±1.3%.
FLOW CHARACTERISTICS NEAR THE "INTERFERENCE KNOT POINT" INSIDE A DIAMOND-SHAPED CYLINDER BUNDLE
351-364
10.1615/JFlowVisImageProc.v15.i4.60
Shinji
Shigeyama
Fukuyama University, Gakuen-cho, Fukuyama, Hiroshima, 729-0292, JAPAN
Tomonori
Wakabayashi
Koseikensetsu Company, Higashi-ku, Hiroshima, 732-0056, JAPAN
The interaction between the oscillating jet and the wedge produces a fluctuating flow field outside the jet which in turn affects the motion of the jet. However, microscopic evidence of these phenomena remains undisclosed. In the present study, an optical system-operated PIV technique was employed to obtain the time-wise variations of both the velocity-vector and vorticity distributions near an "interference knot point" inside a diamond-shaped cylinder bundle. In conclusion, the micro PIV measurements have for the first time disclosed the location and flow process characteristics of the edge-tone source. In addition, the micro flow behavior of reciprocating migration of the conjunct separation vortex pair over the rear edge of the third-row cylinder is confirmed as the mechanism of flip-flow oscillations induced by the edge tone phenomenon.