Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
11
4
2004
AN OPTICAL METHOD FOR LOCAL EQUIVALENCE RATIO MEASUREMENTS APPLIED TO HYDRAULIC SIMULATION OF A RAMJET COMBUSTION CHAMBER
11
10.1615/JFlowVisImageProc.v11.i4.10
G.
Heid
Office National d’Etudes et de Recherches Aerospatiales, Toulouse, France
Hydraulic simulation is a very useful tool to predict global performances of ramjet combustion chambers. Optical techniques can give a lot of information concerning the structure of the flow. In the special case of combustion chambers, it is possible to obtain a spatial repartition of local equivalence ratio and to predict combustion efficiency. This paper presents a ramjet research chamber with two lateral inlets specifically designed for being installed on a hydraulic test rig in order to obtain an experimental database for validating numerical codes. Visualizations are presented and an optical method using laser tomography, LIF and digital acquisition and processing is developed. Experimental procedures are detailed and results concerning local air and fuel flow rates, and local equivalence ratios or mixture fuel/air ratios are analyzed. In addition, an ONERA 's CFD code is presented and the calculated results are compared with experimental data with a rather good agreement.
AUTOMATIC RECOGNITION OF TWO-DIMENSIONAL VORTICES BY DIGITAL IMAGE PROCESSING
11
10.1615/JFlowVisImageProc.v11.i4.20
Shyh-Ming
Sheu
Department of Engineering Science, National Cheng Kung University, Tainan, Taiwan, 701
Jung-Hua
Chou
Department of Engineering Science, National Cheng Kung University, Tainan, Taiwan, 701
In this study, a digital image processing method has been developed to detect automatically the vortex structure behind a circular cylinder. The vortex recognition algorithm is based on the special features of a typical vortex; namely, the circular-like, elliptic-like, and/or the spiral-like characteristics extracted from the geometrical features of the vortex. The algorithm includes two parts; namely, pre-processing and vortex structure recognition. The results indicate that for a 256 × 240 image, all the vortices in the image can be detected in about 100 iterations if the noise level is low or moderate. But if the noise level is high and the pre-processing is poorly done, the algorithm is not reliable. The same situation occurs also if there are break points due to thinning or skeletonizing. These are the limitations of the present algorithm.
PLATE HEAT EXCHANGERS FOR OCEAN THERMAL ENERGY CONVERSION
17
10.1615/JFlowVisImageProc.v11.i4.30
M. H.
Al-Hajeri
Mechanical Power Engineering, Faculty of Technical Studies, P.O.Box 34000 Roudha, Kuwait
A.
Witry
Automotive R & D Center, Windsor, Canada
Ocean Thermal Energy Conversion (OTEC) utilizes the temperature difference between the warm surface seawater and cold deep ocean water to generate electricity. The heat exchanger in an OTEC power plant is significant as it exchanges a large quantity (nearly 40-50 times of the gross power) of heat energy due to the low thermal efficiency of the power cycle. Nearly 30-40% of the total cost of the plant should be allotted to this single component. For the present, 1-MW OTEC plant plate heat exchangers are used both as an evaporator and a condenser.
This paper reports a Computational Fluid Dynamics (CFD) investigation for a dimple plate heat exchanger. The analysis uses the Log Mean Temperature Difference Method (LMTD) in all its calculations. Whilst the shell side flow highly resembles the flow over a rough or wavy plate, the tube side passage in these represents the flow over short hexagonal tube banks with the flow across the sectional areas between the hexagons having the shape of a benzene ring. The CFD code employed is Fluent 5 using the Re-Normalization Group (RNG) turbulence model and the two-layer zonal model for near wall areas on the shell side. For tube side flow, the normal k-ε turbulence model is used with a turbulent Prandtl number of 0.63 suggested for flow in tube banks by the literature.
TWO-DIMENSIONAL POISEUILLE FLOW IN A GROOVED CHANNEL
11
10.1615/JFlowVisImageProc.v11.i4.40
F.
Billy
Laboratoire d'Etudes Aerodynamiques (LEA), UMR CNRS 6609, Blv. Marie & Pierre Curie, B.P. 30179, 86962 Futuroscope Chasseneuil Cedex, France
G.
Pineau
Laboratoire d'Etudes Aerodynamiques (LEA), UMR CNRS 6609, Blv. Marie & Pierre Curie, B.P. 30179, 86962 Futuroscope Chasseneuil Cedex, France
L.
David
Laboratoire d'Etudes Aerodynamiques (LEA), UMR CNRS 6609, Blv. Marie & Pierre Curie, B.P. 30179, 86962 Futuroscope Chasseneuil Cedex, France
M.
Arghir
Laboratoire de Mecanique des Solides (LMS), UMR CNRS 6610, Blv. Marie & Pierre Curie, B.P. 30179, 86962 Futuroscope Chasseneuil Cedex, France
This paper describes a Poiseuille flow between two walls, one of which has grooves normal to the streamwise direction. Three Reynolds numbers are studied (Re = 1000, 5000, 10000) and comparisons between visualization and the velocimetry measurements are presented. The visualization is performed by particle-streak visualization and measurement method is Particle Image Velocimetry (P.I. V.). Measurements enabled the detection of coherent structures and the evolution of velocity in the cavities and in the gap. The present study has been developed to demonstrate that it can provide accurate data in micro-grooves for future experiments with a Couette flow.
HIGH-SPEED COLOR INTERFEROMETRY
11
10.1615/JFlowVisImageProc.v11.i4.50
Jean-Michel
Desse
ONERA, The French Aerospace Lab, 5, boulevard Paul Painleve, F-59045 Lille Cedex, France
This paper presents the improvements brought by ONERA in differential and absolute color interferometry. When the optical technique produces differential measurements, a polarized white light source and one or two Wollaston prisms are used. High-speed interferograms of the flow downstream of a circular base are recorded with a camera at 35,000 frames per second with a 750 nanosecond exposure time for each frame. Unfortunately, as the optical technique yields differential measurements, it is necessary to integrate the data, which results in some inaccuracy in the measurements. Our latest work has thus led us to develop true color real-time holographic interferometry, which allows a direct observation through a reference hologram and makes it possible to take an ultra-high-speed movie of the interferogram of a changing phenomenon. High-speed interferograms have been obtained around a circular cylinder. Using color in this technique is primordial because it combines the advantages of differential interferometry with those of monochromatic holographic interferometry. Color holographic interferometry generates the achromatic fringe and also provides absolute data throughout the entire field of observation. Results show that this technique is an efficient tool for analyzing and characterizing unsteady aerodynamic wake flows in a large field and it could well be the basis for a method of analyzing unsteady 3D flows.
INVESTIGATION OF NATURAL CONVECTION IN VERTICAL CHANNELS BY SCHLIEREN AND HOLOGRAPHIC INTERFEROMETRY
11
10.1615/JFlowVisImageProc.v11.i4.60
Dario
Ambrosini
INFM-Dipartimento di Energetica, Universita dell’Aquila Loc. Monteluco di Roio, I-67040 Roio Poggio (AQ), Italy
Domenica
Paoletti
INFM-Dipartimento di Energetica, Universita dell'Aquila Loc. Monteluco di Roio, I-67040 Roio Poggio (AQ), Italy
Giovanni
Tanda
DIME, Università degli Studi di Genova
Heat transfer phenomena, which frequently involve convection, are usually described through a connective heat-transfer coefficient h. Precise measurement of h is difficult, since calculation requires knowledge of the temperature gradient between the solid surface and the fluid, measured, possibly, without disturbing the thermal layer. Optical techniques are powerful tools in experimental analysis because of their non-disturbing nature. In this paper, natural convection heat transfer in vertical channels is investigated by applying two different optical techniques, namely, schlieren and holographic interferometry. Experiments were conducted at DITEC, University of Geneva (Italy) and at the Energetic Department of the University of L 'Aquila (Italy) on the same test section. The obtained results are discussed and compared.
DETAILS OF IMAGE PROCESSING PROCEDURE FOR VALIDATION OF A SINGLE CAMERA DGV SYSTEM
22
10.1615/JFlowVisImageProc.v11.i4.70
Ph.
Wernert
French-German Research Institute of Saint-Louis (ISL), Saint-Louis, France
B.
Martinez
ISL, 5 rue du général Cassagnou, Saint-Louis, France
T.
Gauthier
French-German Research Institute of Saint-Louis (ISL), Saint-Louis, France
F.
Guermeur
FEMTO-ST Institute, Univ. Bourgogne Franche-Comté, CNRS, Belfort, France
A Doppler Global Velocimetry (DGV) system based on a cw Argon laser and a single CCD camera has been developed at ISL. In this paper, details of the image processing procedure used to validate this system on a rotating disc are given. The results show a very close agreement between measured and theoretical velocity distributions. An example of measurement on a cross section of a jet flow is also described.