Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
11
1
2004
COMPUTATIONAL VISUALIZATION OF SEPARATED/REATTACHED TRANSITIONAL FLOWS ON A BLUNT PLATE
28
10.1615/JFlowVisImageProc.v11.i1.10
Ibrahim E.
Abdalla
Department of Aeronautical and Automotive Engineering, Loughborough University, Loughborough LE11 3TU, U.K.
Zhiyin
Yang
Thermo-fluid Mechanics Research Centre (TFMRC), Department of Engineering and Design, School of Engineering and Informatics, University of Sussex, Brighton BN1 9QT, United Kingdom
It is well known that large-scale organized motions, usually called coherent structures, exist in many transitional and turbulent flows (if not all). The topology and range of scales of those large-scale structures change widely from flow to flow such as counter-rotating vortices in wake flows, streaks and hairpin vortices in turbulent boundary layers. However, it is not well established what kind of large-scale structures exists in separated/reattached transitional flows.
Large-eddy simulation with a dynamic subgrid-scale model is employed in the current study to investigate the physics of transitional separating/reattaching flows over a blunt plate held normal to a uniform stream. The Reynolds number based on the uniform inlet velocity and the plate thickness is 6500. Statistics of the LES are found to be in acceptable agreement with the available experimental data in the laminar, transitional, and turbulent flow regions. The entire transition process leading to breakdown to turbulence has been shown by flow visualization and large-scale structures have been identified at different stages of the transition process of the separating/reattaching flow. The well-known hairpin vortices commonly associated with boundary-layer transition on a flat plate have been clearly shown at about the mean reattachment point and more large-scale structures are presented as well. The large-scale structures are noticed to persist a considerable distance downstream of reattachment before they eventually break into smaller-scale turbulent structures. In addition, it may shed light on the transition mechanisms and the nature of instabilities involved to understand the formation of these large-scale structures, their spatial and temporal evolution and eventual break-up into smaller structures.
BUBBLE BOUNDARY LAYER FORMED BY SIDE GAS INJECTION IN LADLE SYSTEMS WITH THROUGHFLOW
14
10.1615/JFlowVisImageProc.v11.i1.20
Ku-Ho
Su
Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2125, USA
Wen-Jei
Yang
Department of Mechanical Engineering and Applied Mechanics University of Michigan, Ann Arbor, Michigan 48109-2125, U.S.A.
Jr-Ming
Miao
Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2125, USA
The present study employs an air—water cold model to simulate a gas-stirred ladle system with throughflow in a novel steel—making process. The bubble boundary layer is formed by the injection of air through a nozzle installed on an unheated vertical wall into a recirculating flow. Flow visualization by means of direct photography of the two-phase flow region is performed while the depth of the nozzle and the rate of air injection are varied. The bubble boundary-layer thickness is determined which is the distance from the surface to a locus separating the single-phase core in the recirculating flow from the bubble boundary. Both the growth rate and the local average ascending velocity of bubbles in the boundary layer are also measured and their empirical formulas are derived. In addition, five dimensionless parameters governing bubble growth are identified as gas Reynolds number, viscosity ratio, buoyancy number, Weber number, and Froude number. An empirical equation is derived to correlate the experimental data for the bubble boundary-layer thickness. It is disclosed that for all gas injection rates, each bubble boundary layer resembles the hydrodynamic boundary in natural convection over a heated vertical plate.
TEMPERATURE-GRADIENT CONTROL OF FLOW SEPARATION PHENOMENON ON A CURVED SURFACE
10
10.1615/JFlowVisImageProc.v11.i1.30
Wen-Jei
Yang
Department of Mechanical Engineering and Applied Mechanics University of Michigan, Ann Arbor, Michigan 48109-2125, U.S.A.
A numerical study is performed to investigate steady-state thermal and fluid flow transport phenomena of the vertical free jet, which is placed to the surface with the longitudinal convex curvature. Emphasis is placed on the effects of the Reynolds number, Re, and temperature difference between the jet and the heating surface, ∆T, on velocity and thermal fields. It is found that (i) the flow direction of the jet along the curved surface is controlled by Re and ∆T, (ii) as the curved surface is strongly heated, the separation flow is suppressed, resulting in the flow attached on the surface, and (iii) the attached flow is changed to the separated flow with an increase in the Reynolds number.
DIGITAL HOLOGRAPHIC PARTICLE IMAGE VELOCIMETRY: 3D VELOCITY FIELD EXTRACTION USING CORRELATION
20
10.1615/JFlowVisImageProc.v11.i1.40
Corinne
Fournier
Laboratoire Traitement du Signal et Instrumentation, UMR CNRS 5516 Universite J. Monnet 23, rue du Dr P. Michelon 42023 Saint-Etienne cedex 2, France
Christophe
Ducottet
Laboratoire Traitement du Signal et Instrumentation, UMR CNRS 5516 Universite J. Monnet 23, rue du Dr P. Michelon 42023 Saint-Etienne cedex 2, France
Thierry
Fournel
Laboratoire Traitement du Signal et Instrumentation, UMR CNRS 5516 Universite J. Monnet 23, rue du Dr P. Michelon 42023 Saint-Etienne cedex 2, France
Digital holography is used to extend 2D Particle Image Velocimetry to volumic field measurements thanks to the use of correlation. The flow seeded with particles is analyzed from two successive holograms recorded by in-line holography directly on a numerical sensor. The holograms are then processed in order to extract the 3D displacements.
The principle of the algorithm is to represent a pattern (i.e., the particles enclosed in a given 3D interrogation cell) by means of a binary plane mask. The localization of the pattern in each of the two holograms is computed by cross-correlation of the mask in the reconstructed spaces.
The originality of the approach lies in the process of localization of a set of particles. The feasibility is validated by tests carried out in controlled conditions.
EFFECTS OF BUBBLE SHAPE ASSUMPTION ON SINGLE BUBBLE GROWTH BEHAVIOR IN NUCLEATE POOL BOILING
15
10.1615/JFlowVisImageProc.v11.i1.50
Jeongbae
Kim
Department of Mechanical Engineering, Two-phase Flow Lab., Pohang University of Science and Technology, San 31, Hyoja Dong, Pohang 790-784, Korea
Han Choon
Lee
Department of Mechanical Engineering, Pohang University of Science and Technology San 31, Hyoja Dong, Pohang 790-784, Korea
Byung Do
Oh
Department of Mechanical Engineering, Pohang University of Science and Technology San 31, Hyoja Dong, Pohang 790-784, Korea
Moo Hwan
Kim
Division of Advanced Nuclear Engineering, POSTECH, Pohang, Gyeongbuk 37673, Republic of Korea; Department of Mechanical Engineering, POSTECH, Pohang, Gyeongbuk 37673, Republic of Korea; Department of Mechanical Engineering, Pohang University of Science and Technology, San 31, Hyoja Dong, Pohang, 790-784, South Korea
Analytical research was performed to show the effects of bubble shape assumption on the equivalent bubble radius and heat flow rate behavior during bubble growth, based on experimental results for saturated nucleate pool boiling. The equivalent bubble radius was calculated from bubble images captured during the growth phase using the shape assumption for bubble geometry. The heat flow rate was measured using a microscale heater array and a Wheatstone bridge circuit controller. A theoretical analysis was then performed to illustrate that the form of the bubble shape assumption is very important when analyzing single bubble growth behavior.