Journal of Visualization - Volume 8, issue 2

Authors: Wernert, P. | Martinez, B.

Article Type: Research Article

Abstract: A DGV system using a continuous wave Argon laser and an optical arrangement with a single intensified camera has been set up at the ISL blow-down supersonic wind tunnel. The first tests have been performed over a 12.5° 2D wedge at a freestream Mach number of 2. A mean velocity field has been calculated from 28 individual measurements. When compared to the theoretical velocity distribution, deviations of 8% to 15% have been obtained. Preliminary tests have …also been performed on a missile-like model equipped with a lateral jet system. Individual as well as mean velocity fields are presented. Show more

Keywords: Doppler global velocimetry, Supersonic flow, Wind tunnel, Wedge, Side jet

Citation: Journal of Visualization, vol. 8, no. 2, pp. 161-168, 2005

Authors: Gregory, J. W. | Sullivan, J. P. | Raghu, S.

Article Type: Research Article

Abstract: The fluidic oscillator is a device that generates an oscillating jet when supplied with fluid at pressure. The oscillator has no moving parts – the creation of the unsteady jet is based solely on fluid-dynamic interactions. Fluidic oscillators can operate at frequencies ranging up to 20 kHz, and are useful for flow control applications. The fluidic oscillator evaluated in the current study is comprised of two fluid jets that interact in an internal mixing chamber, producing …the oscillating jet at the exit. Both porous pressure-sensitive paint (PSP) and dye-colored water flow are used to visualize the internal and external fluid dynamics of the oscillator. Porous PSP formulations have been shown to have frequency responses on the order of 100 kHz, which is more than adequate for visualizing the fluidic oscillations. In order to provide high-contrast PSP data in these tests, one of the internal jets of the fluidic oscillator is supplied with oxygen, and the other with nitrogen. Results indicate that two counter-rotating vortices within the mixing chamber drive the oscillations. It is also shown that the fluidic oscillator possesses excellent mixing characteristics. Show more

Keywords: Fluidic oscillator, Pressure-sensitive paint, Fluid mixing, Flow control

Citation: Journal of Visualization, vol. 8, no. 2, pp. 169-176, 2005

Authors: Christensen, K. T. | Wu, Y.

Article Type: Research Article

Abstract: High-resolution particle-image velocimetry (PIV) measurements are made in the streamwise – wall-normal plane of turbulent channel flow at Re_{&tau;} =566, 1184 and 1759, facilitating documentation of the population trends and core diameters of small-scale spanwise vortices. Swirling strength, an unambiguous vortex-identification criterion and hence a local marker of rotation, is used to extract small-scale spanwise vortex cores from the instantaneous velocity fields. Once the small-scale vortices are properly extracted from …the PIV realizations, their characteristics are studied in detail. The present results indicate that the very-near-wall region (y < 0.1 h) is densely populated by spanwise vortices with clockwise (negative) rotation. This behavior supports the notion that hairpin-like vortices are generated very close to the wall and grow into the outer layer as they advect downstream. In contrast, counterclockwise (positive) spanwise vortices are scarce in the very-near-wall region, but their presence steadily increases within the logarithmic layer presumably due to a localized generation mechanism. The average core diameter of negative spanwise vortices is found to be larger than the average diameter of positive vortices, with few positive vortices having core diameters exceeding 80 y_* . Show more

Keywords: Turbulence structure, Vortex visualization, Wall turbulence, PIV

Citation: Journal of Visualization, vol. 8, no. 2, pp. 177-185, 2005

Authors: Mueller, Thomas J.

Article Type: Research Article

Abstract: The 11th International Symposium on Flow Visualization (ISFV) was held at Notre Dame, IN, USA, August 8–12, 2004. The Symposium attracted 236 participants from around the world. The 52 Technical Sessions and two Poster Sessions covered a wide range of topics as indicated in the Keywords. Of the 182 submitted papers, 162 were presented. The presented papers included 8 invited lectures. Each morning and afternoon began with an invited lecture by an outstanding, recognized leader in …the field. Toshio Kobayashi received the Leonardo da Vinci Award, an engraved plate, and presented the Leonardo da Vinci Memorial Lecture on "High-performance Computing and Visualization of Unsteady Turbulent Flows." Toshio Kobayashi is very well known for his outstanding contributions in computational science and flow visualization as well as his leadership in organizing conferences, workshops, and symposia on flow visualization. Ronald J. Adrian discussed "Visualization in Extreme Environments," Rolf H. Engler described "Pressure-sensitive Paints and Temperature-sensitive Paints in Quantitative Wind Tunnel Studies," William K. Blake explained "Cavitation as Flow Visualization Seeding," Giovanni M. Carlomagno discussed "The Use of Colors in Thermo-fluid Dynamic Studies," Ajit Yoganathan presented "A Gallery of Cardiovascular Fluid Flow Fields: From Heart Valves to Congenital Heart Disease," Richard B. Miles described "Flow Visualization by Filtered Molecular and Particular Scattering," and Thomas C. Gruber Jr., displayed a technique for "Visualization of Foreign Gases in Atmospheric Air." At the end of the last day, Jurgen Kompenhaus from DLR discussed the 12th ISFV to be held in Germany in 2006. After this presentation there was a tour of the Hessert Laboratory for Aerospace Research. Show more

Keywords: Direct injection, Electronic sparks and discharge, Holography and holographic interferometry, Interferometry, Laser sheet imaging, Laser induced fluorescence, Particle image velocimetry, Shadowgraphy and Schlieren, Mechanical tufts, liquid indicators, and liquid crystals, Thermal and mass transfer indicators (thermography, sublimation, luminescent paints and pressure- and temperature- sensitive paints, Image processing and image assisted methods, Graphical display of data sets, Numerical flow visualization, CFD, DNS, and LES

Citation: Journal of Visualization, vol. 8, no. 2, pp. 187-191, 2005