Journal of Visualization - Volume 12, issue 3

Article Type: Other

Citation: Journal of Visualization, vol. 12, no. 3, pp. i-ii, 2009

Authors: Fohanno, S. | Polidori, G. | Popa, C. V.

Article Type: Research Article

Citation: Journal of Visualization, vol. 12, no. 3, pp. 191-191, 2009

Authors: Dubois, J. | Amielh, M. | Anselmet, F. | Gentilhomme, O.

Article Type: Research Article

Citation: Journal of Visualization, vol. 12, no. 3, pp. 192-192, 2009

Authors: Zou, L. | Lin, Y. F.

Article Type: Research Article

Citation: Journal of Visualization, vol. 12, no. 3, pp. 193-194, 2009

Authors: Tandiono, | Winoto, S. H. | Shah, D. A.

Article Type: Research Article

Abstract: Shear stress distributions were obtained from velocity measurements in a concave surface boundary layer flow in the presence of Görtler vortices by means of a single hot-wire probe for several streamwise (x) locations. A set of vertical wires of 0.20 mm diameter were positioned at a distance of 10 mm upstream from the leading edge of a concave surface of radius of curvature R = 1.0 m to pre-set the wavelength of the vortices so to obtain the most amplified …wavelength Görtler vortices. Consequently, the wavelength of the vortices was set equal to the wire spacing and preserved downstream. In addition to the high shear regions near the wall, one positive peak at the head of the mushroom-like structures and two relatively weak negative peaks at the vicinity of the low-speed streaks are found in the iso-∂u/∂y contours. They are believed to be related to the formation of the inflectional point in the velocity profile across boundary layer. The occurrence of the inflection points in the spanwise distributions of streamwise velocity component u is associated with the appearance of the second peak of the ∂u/∂z shear near the boundary layer edge. The nonlinear effect of Görtler instability is to increase the wall shear stress, and further enhancement beyond the turbulent values is due to the presence of secondary instability. Show more

Keywords: Görtler vortices, Concave surface, Shear stress, Boundary layer flow

Citation: Journal of Visualization, vol. 12, no. 3, pp. 195-202, 2009

Authors: Kim, Y. –J. | Okamoto, K. | Ko, H. S.

Article Type: Research Article

Abstract: Velocity and density distributions of a high-speed and initial CO_{2} jet flow have been analyzed concurrently by a developed three-dimensional digital speckle tomography and a particle image velocimetry (PIV). Two high-speed cameras have been used for the tomography and one for the PIV since a shape of a nozzle for the jet flow is bilaterally symmetric and the starting flow is fast and unsteady. The speckle movements between no flow and CO_{2} jet …flow have been obtained by a cross-correlation tracking method so that those distances can be transferred to deflection angles of laser rays for density gradients. The three-dimensional density fields for the high-speed CO_{2} jet flow have been reconstructed from the deflection angles by the real-time tomography method, and the two-dimensional velocity fields have been calculated by the PIV method concurrently and instantaneously. Show more

Keywords: Flow Visualization, Digital Speckle System, Tomography, Particle Image Velocimetry (PIV), Carbon Dioxide (CO_{2})

Citation: Journal of Visualization, vol. 12, no. 3, pp. 203-215, 2009

Authors: Ohmi, K. | Panday, S. P.

Article Type: Research Article

Abstract: A new concept genetic algorithm (GA) has been implemented and tested for the use in the 2-D and 3-D Particle Tracking Velocimetry (PTV). The algorithm is applicable to particle images with larger (greater than 2000) number of particles without losing the excellent accuracy in the particle matching results. This is mainly due to a new fitness function as well as unique genetic operations devised especially for the purpose of particle matching problem. The new fitness function …is based on the relaxation of movement of a group of particles and is particularly suited for an increased density of particle images. The unique genetic operations give rise to the concentration of more fit genes in the forward part of the gene strings where the crossover and mutation processes are suppressed. The new algorithm also profits from the new genetic encoding scheme which can deal with the loss-of-pair particles (i.e., those particles which exist in one frame but do not have their matching pair in the other frame), a typical problem in the real image particle tracking velocimetry. In the present study, the new method is tested with 2-D and 3-D synthetic as well as real particle images with a large number of particles. Show more

Keywords: Particle tracking velocimetry, 2-D PTV, 3-D PTV, Particle matching problem, Genetic algorithm

Citation: Journal of Visualization, vol. 12, no. 3, pp. 217-232, 2009

Authors: Zare-Behtash, H. | Gongora-Orozco, N. | Kontis, K.

Article Type: Research Article

Abstract: The physics of compressible vortex loops generated due to the rolling up of the shear layer upon the diffraction of a shock wave from a shock tube is far from being understood, especially when shock-vortex interactions are involved. This is mainly due to the lack of global quantitative data available which characterizes the flow. The present study involves the usage of the PIV technique to characterize the velocity and vorticity of compressible vortex loops formed at …incident shock Mach numbers of M = 1.54 and 1.66. Another perk of the PIV technique over purely qualitative methods, which has been demonstrated in the current study, is that at the same time the results also provide a clear image of the various flow features. Techniques such as schlieren and shadowgraph rely on density gradients present in the flow and fail to capture regions of the flow influenced by the primary flow structure which would have relatively lower pressure and density. Various vortex loops, namely, square, elliptic and circular, were generated using different shape adaptors fitted to the end of the shock tube. The formation of a coaxial vortex loop with opposite circulation along with the generation of a third stronger vortex loop ahead of the primary with same circulation direction are of the interesting findings of the current study. Show more

Keywords: PIV, Shock Tube, Compressible Vortex Loop, Secondary Vortex Loop

Citation: Journal of Visualization, vol. 12, no. 3, pp. 233-240, 2009

Authors: Goubergrits,, L. | Weber, S. | Petz, Ch. | Hege, H-Ch. | Spuler, A. | Poethke, J. | Berthe, A. | Kertzscher, U.

Article Type: Research Article

Abstract: Flow visualization of a near wall flow is of great importance in the field of biofluid mechanics in general and for studies of pathologic vessel enlargements (aneurysms) particularly. Wall shear stress (WSS) is one of the important hemodynamic parameters implicated in aneurysm growth and rupture. The WSS distributions in anatomically realistic vessel models are normally investigated by computational fluid dynamics (CFD). However, the results of CFD flow studies should be validated. The recently proposed Wall-PIV method …was first applied in an enlarged transparent model of a cerebri anterior artery terminal aneurysm made of silicon rubber. This new method, called Wall-PIV, allows the investigation of a flow adjacent to transparent surfaces with two finite radii of curvature (vaulted walls). Using an optical method which allows the observation of particles up to a predefined depth enables the visualization solely of the boundary layer flow. This is accomplished by adding a specific molecular dye to the fluid which absorbs the monochromatic light used to illuminate the region of observation. The results of the Wall-PIV flow visualization were qualitatively compared with the results of the CFD flow simulation under steady flow conditions. The CFD study was performed using the program FLUENT®. The results of the CFD simulation were visualized using the line integral convolution (LIC) method with a visualization tool from AMIRA®. The comparison found a very good agreement between experimental and numerical results. Show more

Keywords: PIV, Wall Shear Flow, Molecular Dye, LIC Visualization, CFD

Citation: Journal of Visualization, vol. 12, no. 3, pp. 241-250, 2009

Authors: Marynowski, T. | Desevaux, P. | Mercadier, Y.

Article Type: Research Article

Abstract: The present study deals with the visualization of the droplet condensation phenomenon that can occur in ejectors powered by moist air. The condensation process is visualized through a numerical model of non-equilibrium condensation in high speed flows implemented by the present authors in a CFD code. The evolution of the region of condensation in the ejector with the primary stagnation pressure is examined both in the case without secondary flows and in the case with free …entrainment of induced air. Laser tomography visualization is used to validate the computational results. The effects of some parameters such as the primary stagnation pressure and the humidity ratio in the primary and secondary air flows are also examined. Limitations of the present numerical model are discussed. Show more

Keywords: Ejector, Supersonic flow, Condensation, Moist air, CFD, Laser tomography

Citation: Journal of Visualization, vol. 12, no. 3, pp. 251-258, 2009