Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
9
1
2002
ANALYSIS OF SYMMETRIC MULTIWAVELETS AND ITS APPLICATION FOR IMAGE COMPRESSION
10
10.1615/JFlowVisImageProc.v9.i1.10
Chen
Jiazhong
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
Xiaocheng
He
National Storage System Laboratory, Department of Computer Science and Engineering, Huazhong University of Science & Technology, Wuhan, Hubei 430074, P. R. China
Li
Jun
National Storage System Laboratory, Department of Computer Science and Engineering, Huazhong University of Science & Technology, Wuhan, Hubei 430074, P. R. China
Multiwavelets are the new addition to the body of wavelet theory. It is also based on the idea of multiresolution analysis (MRA). An MRA is usually generated by one scaling function. However, such wavelets cannot possess the properties of compact support, linear phase, and orthogonality simultaneously. Realized as matrix-valued filterbanks leading to wavelet bases, multiwavelets can offer these three properties simultaneously which are strongly desired in many applications, such as a fast multiresolution pyramid decomposition algorithm of image with the 2 ґ 2 matrix. To succeed using the EZW algorithms, we wish there still are some of the relationships between ancestors and their offspring. But the relationship is not very clear after the conventional iteration of multiwavelet decomposition which is similar to the scalar wavelet decomposition, and the encoding effect and efficiency are not very good. Therefore, this paper presents full new decomposition and quantization methods adapt to the symmetric property of multiwavelets. Extensive experimental results demonstrate that our techniques exhibit performance equal or superior to the conventional decomposition methods.
VISUALIZATION OF THE EFFECT OF DISPERSED PARTICLES ON HEAT TRANSFER FROM AN IMPINGING JET
14
10.1615/JFlowVisImageProc.v9.i1.20
Julien
Reveillon
CORIA-UMR 6614 – Normandie Université, CNRS-Université et INSA de
Rouen, Campus Universitaire du Madrillet, 76800 Saint Etienne du Rouvray,
France
K.
Canneviere
University of Rouen, UMR CNRS 6614 CORIA, Avenue de l’Universite - BP 8, FR-76801 Saint Etienne du Rouvray Cedex, France
The objective of this paper is to show the effect of a solid (or nonvaporizing) dipersed phase on the turbulent structures of an impinging jet. Direct numerical simulation (DNS) has been carried out to fully describe the turbulence evolution from the jet destabilization up to the breakup of the structures. A Lagrangian solver has been coupled to the DNS code to describe precisely the interactions between the particles and the gas. Two kinds of particles have been considered: (1) incident particles that are embedded in the jet at the injection level. These particles modify strongly the turbulence characteristics and increase heat transfer from the jet; (2) when incident particles are impacting on the wall, very small ejecta (particles of carbon) may be emitted and, in this case, heat fluxes decrease because of strong turbulent mixing close to the wall. Creation of small swirling structures as well as core of recirculation close to the wall could be detected thanks to numerical visualization of nonstationary flows.
A NEW ALGORITHM FOR ANALYZING SHADOWGRAPH IMAGES
27
10.1615/JFlowVisImageProc.v9.i1.30
John C.
Patterson
Centre for Wind, Waves and Water, School of Civil Engineering, The University of Sydney
Darlington, NSW 2006, Australia
G. B.
Brassington
College of Oceanic and Atmospheric Sciences, Oregon State University, 104 Ocean Admin. Bldg., Corvallis, OREGON 97331, USA
M.
Lee
School of Engineering, James Cook University
A new algorithm for constructing shadowgraph images from approximate density fields is presented with the primary motivation of performing accurate laboratory shadowgraph analysis. Available image construction algorithms are noisy and produce discontinuous errors even for small gradient density fields. Discontinuity errors are serious, being indistinguishable from real optical focusing which occurs frequently. The new algorithm completely eliminates these errors. Image improvements are demonstrated for realistic synthetic refractive index fields. Favorable comparisons of the new algorithm are also demonstrated with laboratory shadowgraph of natural convection flows in a cavity which feature large density gradients. A second motivation of the paper is to accurately analyze approximate shadowgraph images derived from a linearized analytical model for refraction. The linearized shadowgraph images are correlated with the artificial shadowgraph images of the new algorithm. Preliminary results indicate that quantitative information from shadowgraph images of larger gradient density fields could be obtained by iterating about the linear solution.
UNUSUAL LASER-SHEET TOMOGRAPHY COUPLED WITH BACKLIGHT IMAGING CONFIGURATIONS TO STUDY THE DIESEL JET STRUCTURE AT THE NOZZLE OUTLET FOR HIGH INJECTION PRESSURES
19
10.1615/JFlowVisImageProc.v9.i1.40
Jérôme
Yon
Normandie Univ, INSA Rouen, UNIROUEN, CNRS, CORIA, 76000 Rouen, France
Jean-Bernard
Blaisot
CORIA-UMR 6614—Normandie Universite, CNRS-Universite et INSA de Rouen, Campus Universitaire du Madrillet, 76800 Saint Etienne du Rouvray,
France
M.
Ledoux
CORIA-UMR CNRS 6614, Universite de Rouen, Site du Madrillet Avenue de l’Universite, BP12 76801 Saint Etienne du Rouvray cedex, France
One of the main goals of the car manufacturer is to build less polluting Diesel engines. In order to control the combustion it is essential to understand the atomization process. It is well known that the behavior of the liquid jet at the nozzle outlet acts directly on the atomization. For high injection pressures, the density of the jet at the injector exit makes it very difficult to study. Among the several technical approaches often used to visualize this dense region of the jet, the most convincing one seems to be laser-light sheet tomography. In this paper, the tomography is used together with short duration non-coherent backlighting. The focal plane displacement effect on the imaging and the modification of the laserlight sheet orientation are the main originalities of this work. These optical configurations have been applied to a 200-mm hole diameter nozzle for injection pressure up to 80 MPa. The changes in the jet structure with different injection pressures and at different injection times are reported. External and internal structures of the jet are pointed out. The visualizations, linked to a ray-tracing simulation, allowed us to design a new model for the Diesel jet structure.
A MASS CONSERVATIVE STREAMLINE TRACKING METHOD FOR TWO DIMENSIONAL CFD VELOCITY FIELDS
13
10.1615/JFlowVisImageProc.v9.i1.50
Zhenquan
Li
School of Computing and Mathematics, Charles Sturt University, Thurgoona, NSW2640, Australia
Mass conservation is a key issue for accurate streamline visualization of flow fields. This paper presents a mass conservative streamline construction method for CFD velocity fields defined at discrete locations on plane. Linear interpolation is used to approximate velocity fields. Demonstration examples show that the method is very accurate.
COHERENT STRUCTURE DYNAMICS IN TURBULENT CHANNEL FLOW
10
10.1615/JFlowVisImageProc.v9.i1.60
Leonardo
Primavera
Fluid Dynamics Laboratory, Universita della Calabria, Via P. Bucci, Cubo 42b, 87036 Rende (Cosenza), Italy
Giancarlo
Alfonsi
Fluid Dynamics Laboratory, Universita della Calabria, Via P. Bucci 42b, 87036 Rende (Cosenza), Italy
The dynamics of coherent structures in the near-wall region of a turbulent channel flow at Reynolds number Re = 40,000 (based on bulk velocity and channel half-width) is investigated. The technique of the Proper Orthogonal Decomposition (POD) is applied to extract the coherent structures of the flow from a turbulent flow database obtained with the use of a finite volume computational code for the numerical integration of the three-dimensional time-dependent incompressible Navier-Stokes equations; for turbulence modeling the LES (Large Eddy Simulation) approach is followed and the RNG (Renormalization Group technique) Sub Grid-Scale closure is used. The three-dimensional time-dependent velocity field is computed and 100 non-dimensional time steps of the turbulent statistically steady state are considered for the decomposition of the flow field. Results are presented in terms of numerical visualizations of streamwise vorticity, showing the temporal dynamics of structures and the different phases of the turbulent activity near the wall.