Begell House Inc.
Journal of Flow Visualization and Image Processing
JFV
1065-3090
15
3
2008
PIXEL QUANTIZATION INFLUENCE ON REAL-TIME CROSS-CORRELATION COMPUTATION FOR AN EMBEDDED PIV CONTROL SYSTEM
181-200
Nabila
Filali
Unité de Métrologie en Mécanique des Fluides et Thermique (UMMFT), 03/UR/11-09, Ecole Nationale d’Ingénieurs de Monastir, Tunisie
Taoufik
Filali
Unité de Métrologie en Mécanique des fluides et Thermique, Monastir University, Tunisia; and Hubert CURIEN Laboratory, Saint-Etienne University, France
Habib Ben
Aissia
National School of Engineers of Monastir, Metrology Research Unit and Energy Systems, 5000 Monastir, Tunisia
Jacques
Jay
Thermal Science Centre of Lyon (CETHIL - UMR CNRS 5008) National Institute of Applied Sciences of Lyon Lyon, France
The main purpose of this paper is to evaluate the measurement efficiency of the PIV (Particle Image Velocimetry) technique in real time. Thus, we propose a new approach using pixel quantization format reduction to process image cross-correlation as well as flow displacement vector validation in real time. To achieve this, two delayed images are acquired and parallely transferred to a hardware system based on FPGA and to a computer. A cross-correlation processing algorithm between the images leads to computing of the displacement vector field. The PIV data validation criteria will be detailed and some of them are selected for implementation. With this contribution hardware needs are slightly dwindled by maintaining the same performance.
ON IDENTIFICATION OF VORTICAL STRUCTURES IN TURBULENT SHEAR FLOW
201-216
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
In the present work, four criteria for vortex detection in turbulent flows are considered. Three of them involve the invariants of the velocity-gradient tensor and one involves the analysis of the Hessian of the pressure. The ability of the different methods in detecting vortical structures in wall-bounded flows — hairpin vortices in particular — is analyzed with the following procedure: i) the flow of a viscous incompressible fluid in a plane channel is simulated numerically with the use of a computational code for numerical integration of the Navier-Stokes equations, based on a mixed spectral-finite difference technique (the approach of the Direct Numerical Simulation is followed); ii) a turbulent-flow database, representing the turbulent statistically steady state of the velocity field through 10 viscous time units, is assembled; iii) all the vortex-identification techniques are applied to the database. It is shown that three of the methods considered give almost equivalent results in identifying hairpin-like vortical structures in the wall region of turbulent channel flow, while one of them gives slightly different results.
PASSIVE TECHNIQUES FOR CONTROL OF TURBULENCE IN WALL-BOUNDED FLOWS
217-234
Giancarlo
Alfonsi
Fluid Dynamics Laboratory, Universita della Calabria, Via P. Bucci 42b, 87036 Rende (Cosenza), Italy
In this paper, the results obtained by the implementation of two widely used passive techniques for control of turbulence in wall-bounded flows — riblets and wall protrusions — are reviewed. The work is limited to the incompressible-flow case. In recent times, much interest has been devoted to active techniques for turbulence control (mainly sensors coupled with actuators) that, in turn, have never led to results comparable with those obtained by passive means. Moreover, with respect to the active, passive techniques can be more easily implemented in flows of applicative interest and their potential in controlling turbulence has been not yet completely explored. A point is made on the interpretation of the physical phenomena that give rise to the wall-protrusion technology for wall-turbulence control, actually offering a different point of view on those phenomena with respect to past researches.
FLOW VISUALIZATION OF SMOKE SCREEN FORMATION FOR A RECTANGULAR VEHICLE IN DYNAMIC MOTION
235-260
Jr-Ming
Miao
Department of Materials Engineering, National PingTung University of Science & Technology, Shuefu Road, Neipu, Pingtung, Taiwan.
Hou-Chei
Chang
Graduate School of Defense Science Studies, Chung Cheng Institute of Technology National Defense University, Taoyuan, 335, Taiwan, R.O.C.
This study uses computational fluid dynamics (CFD) and the dynamics mesh technique to simulate and visualize the unsteady vortex shedding of a smoke screen produced by a smoke-generating vehicle in dynamic motion. The effects of atmospheric wind speed and the speed of the smoke-generating vehicle on the smoke screen transport phenomena are examined. In this study, the smoke screen is released from the base of the vehicle as two parallel jets with a ratio of centerline spacing to nozzle diameter equal to 52. Once the smoke concentrations are obtained from the numerical results, the Bouger-Lambert law is applied to calculate the percentage of visibility degradation at particular axial positions.
Two-dimensional flow variables are solved using the unsteady Reynolds-Averaged Navier-Stokes equation (RANS) with the control volume method. The computational domain is constructed with the conformal hybrid mesh system combined of rectangular grids around the vehicle and triangular grids in the remaining open domain. The buoyancy effect of air and smoke are approximated using the Boussinesq assumption, and the Reynolds stress terms are treated with the RNG κ-ε turbulence model with standard wall functions. The smoke-generating vehicle was simplified as a rectangular cylinder body. The tested atmospheric wind velocity ranged from 1 ms−1 to 9 ms−1 and the speed of the smoke-generating vehicle relative to the leeward wind varied from 3 ms−1 to 9 ms−1 . The velocity ratio (IR) of released smoke to the wind speed ranged within 3.3−30.
Simulation results reveal that the wake flow pattern behind the smoke-generating vehicle is similar to the von Karman street vortex. The amplitude of vortex shedding decreases and gradually changes into a single jet as the speed of the smoke-generating vehicle increases. The percentage of visibility degradation decreases with an increase of the oncoming atmospheric wind speed, regardless of whether the smoke-generating vehicle is in stationary parking or forward motion mode. When the oncoming atmospheric wind speed is below 1 ms−1, driving the vehicle forward at a speed below 7 ms−1 can effectively enhance the performance of smoke screen production within a certain time period. However, there are limits on the speed of the smoke-generating vehicle with respect to the atmospheric wind flow in establishing a smoke screen over a large area.
VISION ALGORITHM FOR SHAPE EVALUATION AND CENTROID DETECTION OF MEAT-PATTIES FROM RANDOMLY PLACED AND SEVERELY OVERLAPPED PATTIES FOR AUTOMATED HANDLING FOR SORTING AND PACKAGING
261-273
Muhammedali
Bharmal
Agilent Technologies (Malaysia)
Although the use of a robot vision system in manufacturing sectors is now a commonplace, however, the technology embodied in these devices is poorly matched to industrial needs of food processors. In particular, vision processing used for feedback to automated food handlers should be programmed to detect the position of a single and isolated object as well as overlapping or occluding objects. In this project, started over a year ago, a vision guidance system is being developed to meet this objective. The system integrates the modified version of the Hough transform algorithm as the main recognition engine, to inspect the physical quality of meat-patties and accurately detect the position of each meat-patty from randomly placed, overlapping, and touching meat-patties. The methods and procedures were tested on commercially produced meat-patties.