Journal of Visualization - Volume 7, issue 2

Authors: Yoshida, Toyoaki

Article Type: Other

Citation: Journal of Visualization, vol. 7, no. 2, pp. 103-103, 2004

Article Type: Other

Citation: Journal of Visualization, vol. 7, no. 2, pp. 105-110, 2004

Authors: Kim, M.J. | Kihm, K.D.

Article Type: Research Article

Abstract: Electro-osmosis is the flow produced by the action of an electric field on a fluid with a net charge, which is created by the Zeta potential and confined in the Debye layer. This basic phenomenon in the electro-kinetic transport plays an important role in the microfluidic systems being explored today because it can be applied to a variety of MEMS devices. This paper presents global and point-wise comparisons of experimental measurements of electro-osmotically driven flows in …elementary microchannel configurations, which are made by photolithography using poly-di-methyl-siloxane (PDMS). To measure full field velocity distributions in PDMS microchannels, a microscopic particle image velocimetry (μ-PIV) system has been developed to track the fluorescent images of 500 nm diameter particles. Comparisons of experimental results among various micro-configurations show feasibilities of the electro-osmotic flows to use for micro-pumping and micro-fluidic flow control. Show more

Keywords: electro-osmotic flow, μ-PIV, microchannel, fluorescent micro-spheres

Citation: Journal of Visualization, vol. 7, no. 2, pp. 111-118, 2004

Authors: Maw, Win Shwe | Fujiwara, Shingo | Takahashi, Tsutomu | Shirakashi, Masataka

Article Type: Research Article

Abstract: In this study, the Hele-Shaw cell is used to examine the effect of fluid elasticity on the flow patterns of two-dimensional potential flow. Flows around a circular cylinder, a square cylinder and flows through abruptly converging-diverging channels (slits) with different throat lengths are tested for water and 0.2 wt % polyacrylamide aqueous solution (PAA-solution). The viscosity of the latter is well modeled by the power law, and the first normal stress difference in the steady shear …flow is around ten times higher than the shear stress. Although the PAA-solution is highly shear-thinning, the flows of PAA-solution well reproduce the two-dimensional potential flow patterns that correspond to the respective flow configurations when the flow rate is very low. The potential flow patterns of PAA solution are disturbed in the opposite way of inertia effect observed for water. The streamlines near the upstream stagnation point of cylinders are shifted upstream separating from the cylinder surface when the flow rate is higher, while streamlines in the wake approach closer to the downstream stagnation point. Streamlines of flow through the slit at flow rates higher than the potential flow region show that a pair of vortices is formed upstream the slit entrance, while the streamlines remain attached to the downstream wall after passing the slit. Show more

Keywords: Hele-Shaw flow, Viscoelastic fluid, Flow around a cylinder, Converging-diverging channel, Weissenberg number

Citation: Journal of Visualization, vol. 7, no. 2, pp. 119-126, 2004

Authors: Chashechkin, Yu.D. | Mitkin, V.V.

Article Type: Research Article

Abstract: The flow pattern around a thin strip horizontally towed at constant velocity in a continuously stratified liquid is visualized by conventional "Vertical slit-Foucault's knife", "Maksoutov's slit-thread" and "horizontal slit-regular grating" methods. Using these sensitive high-resolution methods enables to reveal new kind of the streaky structure including a sequence of thin sloping interfaces both on the strip surface and inside its wake. When velocity or distance from the strip increases, the streaks may …be turned into the sloping or nearly horizontal interfaces. Reconnections of outer edges of the streaks result in appearance of a set of symmetrical "butterfly-like" vortices, which are perturbed by a shear flow inside the downstream wake. Lift forces caused by a slope of the strip produce an asymmetry of the wake and lead to fast degeneration of the streaky structures. Show more

Keywords: Schlieren technique, Stratified fluid, Horizontal strip, Internal waves, Streaky structures

Citation: Journal of Visualization, vol. 7, no. 2, pp. 127-134, 2004

Authors: Fujisawa, N. | Nakamura, K. | Srinivas, K.

Article Type: Research Article

Abstract: The interaction of two parallel plane jets of different velocities is studied by flow visualization and PIV measurement to examine the influence of velocity ratio on the development of jets in the initial region. It is found that the parallel plane jets develop toward the high velocity side and the jet width is reduced with a decrease in the jet velocity ratio. Corresponding to the variation of mean velocity field to the velocity ratio, the magnitudes of …turbulence intensities, Reynolds stress and static pressure are weakened in the merging region of the jets and their peak locations of the properties are shifted to the high velocity side. These results indicate that the interaction of two parallel jets is weakened with a decrease in the velocity ratio of the jets. Show more

Keywords: Parallel jets, Flow measurement, Turbulent flow, PIV, Flow visualization

Citation: Journal of Visualization, vol. 7, no. 2, pp. 135-142, 2004

Authors: Gushchin, V.A. | Kostomarov, A.V. | Matyushin, P.V.

Article Type: Research Article

Abstract: For the detailed investigation of the 3D unsteady incompressible viscous separated fluid flows around a sphere (for 200 ≤ Re ≤ 700) and a circular cylinder (for 200 ≤ Re ≤ 400) the direct numerical simulation and 3D visualization are used. For 3D visualization of the fluid flows around a sphere the definition of vortex core as a connected region containing two negative eigenvalues of the S^2 + Ω^2 tensor is used (where S_{i,j} …and Ω_{i,j} are the rate of strain and the rate of rotation tensors). The formation mechanism of vortices in the sphere wake for Re = 500 is described in detail. For 3D visualization of the fluid flows around a circular cylinder the 3D isosurfaces of the streamwise component of vorticity ω_x are used. Show more

Keywords: 3D Visualization, Sphere, Cylinder, Wake, Vortex structures

Citation: Journal of Visualization, vol. 7, no. 2, pp. 143-150, 2004

Authors: Nishio, Masatomi | Sezaki, Shinji | Nakamura, Hiroaki

Article Type: Research Article

Abstract: The spatial flowfield around a model of the re-entry capsule of the Mars Environmental Survey (MESUR) Pathfinder probe afterbody configuration traveling at a speed of Mach 10 was investigated utilizing the electrical discharge method. The shock shape ahead of the capsule was observed using a technique for visualizing 3-D shock shapes, then the streamline following the shock wave was observed utilizing a technique for visualizing streamlines crossing a shock wave. Subsequently, the flowfield behind the capsule …was observed by applying a technique for visualizing flow patterns. From these observations, the spatial flow construction including the wake region such as a separation, free shear layer, and rear stagnation location behind the capsule was made clear. These experiments utilizing the electrical discharge method qualitatively demonstrated the spatial flow structure before and behind the hypersonic re-entry capsule, which had been very difficult to visualize. These experiments were carried out by using a pulsed facility of 18 ms duration. Show more

Keywords: Hypersonic flow visualization, Electrical discharge method, Re-entry capsule, Wake, Flow structure, Hypersonic flow

Citation: Journal of Visualization, vol. 7, no. 2, pp. 151-158, 2004

Authors: Lee, S.M. | Hwang, J.Y. | Chung, S.H.

Article Type: Research Article

Abstract: A tomographic deconvolution technique using the Fourier transformation has been applied for the reconstruction of asymmetric soot structure. Local soot volume fraction distribution can be identified from line-of-sight integrated data using light extinction measurements with multi-angular scanning. A peak-following interpolation technique was adopted to effectively increase the number of scanning angles. The results showed that the peak-following interpolation has improved the accuracy of reconstruction compared to the arithmetic interpolation in determining the …local soot volume fraction. The measurement from a laser-induced incandescence technique substantiated the validity of the reconstruction technique. Show more

Keywords: Soot, Tomography, Peak-following interpolation, Light extinction

Citation: Journal of Visualization, vol. 7, no. 2, pp. 159-166, 2004

Authors: Carlomagno, G.M.

Article Type: Research Article

Abstract: The 7th International Symposium on Fluid Control, Measurement and Visualization (FLUCOME'03) was held in Sorrento, Italy, from the 25th to the 28th of August 2003. The Symposium attracted, by far, one of the largest number of participants in the history of the meeting. The 232 presented papers were distributed in 52 Technical Sessions which covered the very broad range of topics indicated in the Keywords. At the beginning of each working day, a speaker, selected among …renowned specialists, delivered an authoritative lecture in Plenary Session. Prof. W. Merzkirch discussed Fluid Mechanical Problems in Flow Metering, Prof. C.J. Chen described Some Aspects of Nanotechnology, Microtechnology and Biomedical Applications, and Dr. A. Cogotti treated From Steady-State to Unsteady Aerodynamics and Aeroacoustics. The Evolution of the Testing Environment in the Pininfarina Wind Tunnel while Prof. B.T. Zinn reported on The Real Time Control of the Lean Blow Out Limit in Pre-Mixed Combustors for Reduced NOx Emissions. On the last day, Prof. A. Tamir entertained the audience by considering the interaction between art and science. Show more

Keywords: Aerodynamics, Bioengineering, CFD Applications, CFD Methods, Combustion, Compressible Flows, Cylinder Flows, Flow Control, Flow Measurements, Flow Metering, Flow Visualization, Fluidics, Heat Transfer in External Flows, Heat Transfer in Internal Flows, Hydraulics, Jets, Machine Flows, Micro Flows, Mixed Convection, Natural Convection, Optical Methods, Particle Image Velocimetry, Pneumatic Components, Pneumatics, Separated Flows, Synthetic Jets, Tunnel Testing, Turbulence, Two Phase Flows, Unsteady Aerodynamics

Citation: Journal of Visualization, vol. 7, no. 2, pp. 167-170, 2004