Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
12
1
2005
MULTIPHASE FLOW VISUALIZATION IN MICROCHANNELS USING X-RAY TOMOGRAPHIC MICROSCOPY (XTM)
1-13
S.
Waelchli
Institute of Process Engineering, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland
Philipp Rudolf
von Rohr
Institute of Process Engineering, Swiss Federal Institute of Technology (ETH), Zürich, Sonneggstrasse 3, 8092 Zürich, Switzerland
M.
Stampanoni
Swiss Light Source (SLS), Paul Scherrer Institut (PSI), Villigen, Switzerland
We present a flow visualization technique that provides time-averaged three-dimensional images of stationary multiphase gas—liquid flows in microchannels using X-ray Tomographic Microscopy (XTM). The ability of reconstructing a three-dimensional image of the flow makes XTM a powerful non-destructive investigation method for analysis and study of the flow pattern. Due to several restrictions, this measurement method is applicable for stationary flow patterns only. Comparing the demonstrated XTM results with those obtained by conventional optical flow visualization techniques, XTM is shown to be an adequate flow visualization method for annular flow, which is mostly required in multiphase chemical reactions in microsystems.
DEVELOPMENT OF A NEW INTERFACE FOR NUMERICAL GAS FLOW VISUALIZATION IN HIGH-VOLTAGE CIRCUIT-BREAKERS
15-20
F.
Madani
Centre de Recherche de la Transmission d'Energie AREVA T&D, 130 rue Leon Blum 69611 Villeurbanne Cedex, France
Ph.
Robin-Jouan
Centre de Recherche de la Transmission d'Energie AREVA T&D, 130 rue Leon Blum 69611 Villeurbanne Cedex, France
More and more CFD tools are used to investigate the gas flow behavior during the opening of the high-voltage circuit-breakers with the creation of an electric arc. Gas flow analysis and computation provide the engineers with the information about the gas behavior, the dielectric withstand, and the evolution of the high-temperature areas inside the chambers. Moreover, oriented softwares are extremely important since they could permit rapid investigation and optimization of different shapes of the circuit-breaker parts. The expected functionalities of this tool are: classic analysis of the gas flow, post-treatment of new fields coming from external data base, easy comparison of different configurations of apparatus for different calculated quantities, temporal analysis, video creation, pseudo 3D representation, and parallel analysis of experimental data. The objective of the development at the Switchgear Research Centre of AREVA T&D was to extend this interface, to integrate CAD tools and to interface with other softwares. A first version of such a tool is now available. It has been developed thanks to the software Express from Advanced Visual System Company.
A FAST MACROBLOCK MODE SELECTING METHOD BASED ON SPATIAL-TEMPORAL CORRELATION FOR H.264
21-27
Xiang
Dong
National Storage System Laboratory, Department of Computer Science and Engineering, Huazhong University of Science & Technology, Wuhan, Hubei 430074, P. R. China
Zhou
Jingli
National Storage System Laboratory, Department of Computer Science and Engineering, Huazhong University of Science & Technology, Wuhan, Hubei 430074, P. R. China
Yu
Shengsheng
National Storage System Laboratory, Department of Computer Science and Engineering, Huazhong University of Science & Technology, Wuhan, Hubei 430074, P. R. China
Chen
Jiazhong
National Storage System Laboratory, Department of Computer Science and Engineering, Huazhong University of Science & Technology, Wuhan, Hubei 430074, P. R. China
H.264 is the latest international video coding standard. It adopts tree-structure macroblock partitions in motion-compensated coding modes to improve coding performance. This technology searches all available modes, so the computational cost increases linearly with the number of the allowed modes. In this paper, a fast macroblock mode selecting method based on spatial-temporal correlation for H.264 was proposed. This method efficiently reduces the computational complexity while keeping similar rate-distortion performance and can combine with other fast mode selecting algorithms to further reduce the computational complexity.
OSCILLATIONS AND VORTEX-INDUCED VIBRATIONS OF A TETHERED SPHERE IN A FLOW
29-44
M.
Provansal
Institut de Recherche sur les Phenomenes Hors Equilibre (IRPHE) UMR CNRS 6594, Marseille, France, Technopole de Chateau-Gombert 49 rue F.Joliot-Curie, B.P146 13384 Marseille cedex France
T.
Leweke
Institut de Recherche sur les Phenomenes Hors Equilibre (IRPHE) UMR CNRS 6594, Marseille, France, Technopole de Chateau-Gombert 49 rue F.Joliot-Curie, B.P146 13384 Marseille cedex France
L.
Schouveiler
Institut de Recherche sur les Phenomenes Hors Equilibre (IRPHE) UMR CNRS 6594, Marseille, France, Technopole de Chateau-Gombert 49 rue F.Joliot-Curie, B.P146 13384 Marseille cedex France
C.
Aprile
Institut de Recherche sur les Phenomenes Hors Equilibre (IRPHE) UMR CNRS 6594, Marseille, France, Technopole de Chateau-Gombert 49 rue F.Joliot-Curie, B.P146 13384 Marseille cedex France
The behavior of a tethered sphere in a steady uniform flow has been investigated for two different configurations. Firstly, we consider a flow parallel to the tether in a small vertical water channel and, secondly, we perform experiments in a wind tunnel where the flow is perpendicular to the tether. Above a critical value Uc of the free-stream velocity, the sphere exhibits oscillations induced by the periodic vortex shedding. When the flow is parallel to the tether, new modes of oscillations of the sphere along circular or elliptic trajectories have been observed. The transition from steady to oscillatory movement of the sphere is shown to be hysteretic. The frequency and the amplitude of the oscillations, always locked to the natural frequency of the pendulum constituted by the tethered sphere, have been measured as a function of the reduced velocity. When the flow is perpendicular to the tether, the trajectories of the sphere have been recorded. The amplitude and frequency of the movement as well as the spectral density of the fluctuations of the location have been deduced by image processing.
UNSTEADY DEVELOPMENT OF VORTICAL STRUCTURES IN THE SYMMETRIC NEAR WAKE OF A CYLINDER
45-72
Giancarlo
Alfonsi
Fluid Dynamics Laboratory, Universita della Calabria, Via P. Bucci 42b, 87036 Rende (Cosenza), Italy
The time-dependent Navier-Stokes equations in their streamfunction-vorticity transport form are numerically integrated to explore the early temporal stages of the evolution of vortical structures of different order in the near wake of a circular cylinder. The numerical technique used is a mixed spectral-finite analytic scheme in which the flow fields are expanded in Fourier series along the azimuthal direction and the convolutions arising from the convective terms of the vorticity transport equation are calculated by means of Fast Fourier Transform algorithms. The time advancement is performed by using a fourth-order Runge— Kutta algorithm (first four iterations) and a Predictor—Corrector scheme (subsequent iterations). The time-dependent case of a viscous incompressible fluid flowing around an impulsively started circular cylinder at the Reynolds number Re = 3000 (based on free-stream velocity and cylinder diameter) is considered, with particular attention to the evolution in time of primary, secondary, and tertiary vortices developing in the near wake of the cylinder numerically kept in its symmetric configuration. The results are presented for several time steps of integration mainly in terms of computer-generated images of streamlines and vorticity fields, describing the reciprocal interaction of vortical structures of different order in the near wake of the cylindrical body.
NUMERICAL INVESTIGATION OF GASEOUS MICROCHANNEL FLOW IN TRANSITION REGIMES
73-94
Pei-Yuan
Tzeng
Department of Aeronautical Engineering, Chung Cheng Institute of Technology, National Defense University Ta-Hsi, Tao-Yuan 33509, Taiwan, ROC
Ping-Hsuang
Chen
Chung Cheng Institute of Technology, National Defense University Ta-Hsi, Tao-Yuan 33509, TAIWAN, R.O.C.
Ming-Ho
Liu
Chung Cheng Institute of Technology, National Defense University Ta-Hsi, Tao-Yuan 33509, TAIWAN, R.O.C.
Pressure-driven low subsonic gaseous flows in a microchannel are studied numerically by the Direct Simulation Monte Carlo (DSMC) method. The Variable Hard Sphere (VHS) molecular model and Larsen—Borgnakke procedures are adopted. The Knudsen number (Kn) is adjusted by varying inlet/outlet pressure for a range of transition regimes. Cases of different channel aspect ratios and wall temperatures with the fixed inlet/outlet pressure or constant average pressure-gradient boundary conditions are investigated. The results indicate that both the channel length and heat transfer affect the rarefaction of the flow. The downstream variations in flow properties are strongly dependent on Kn, aspect ratio, and heat transfer, and generally are in qualitative agreement with the Fanno/Rayleigh theory.
NUMERICAL ANALYSIS OF THERMAL-FLUID FLOW BETWEEN STATIONARY AND ROTATING PARALLEL DISKS
95-104
This paper investigates thermal-fluid transport phenomena in a laminar flow between a rotating bottom disk and a stationary upper disk, from whose center a circular jet is impinged on the heated horizontal bottom disk surface. Emphasis is placed on the effects of the Reynolds number, rotational velocity, and disk spacing on both the formations of velocity and thermal fields and the heat-transfer rate along the heated wall surface. The governing equations are discretized by means of a control volume technique and are numerically solved to determine the distributions of the velocity vector and fluid temperature under the appropriate boundary conditions. It is found from the study that (i) the recirculation zone which appears on the stationary disk moves along the outward direction with an increase in the Reynolds number, (ii) when the Reynolds number is increased, heat transfer performance is intensified over the whole disk surface and the minimum value of the heat-transfer rate moves in the downstream direction, and (iii) the heat-transfer rate is induced due to the disk rotation, whose effect becomes larger in the wider disk spacing.