著者

Matsuda Tadashi Sakakibara Jun

出版者

American Institute of Physics

雑誌

Physics of fluids (ISSN:10706631)

巻号頁・発行日

vol.17, no.2, pp.025106, 2005-01

被引用文献数

48 41

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Turbulent vortical structures in a round free jet of water were experimentally visualized by using stereo particle image velocimetry (PIV). A laser light sheet illuminated a cross-sectional plane normal to the axis of the jet, and two charge-coupled device cameras captured particle images in the same region of interest but from different directions. The stereo-PIV algorithm had been applied to obtain two-dimensional, three-component (2D-3C) velocity distributions on various cross-sectional planes along the axis downstream. All nine components of the velocity gradient tensor were reconstructed from time-dependent 2D-3C velocity data by locally assuming Taylor's frozen field hypothesis based on the convective velocity evaluated from the mean flow profile. Isosurfaces of the swirling strength lambdai revealed that the existence of a group of hairpinlike vortex structures was quite evident around the rim of the shear layer of the jet. The center of curvature of the head of the hairpin was typically observed around r/b = 1.5, and the azimuthal spacing between the legs of the hairpin was roughly 0.9b. A similar hairpin structure was estimated by linear stochastic estimation. The typical spacing between the legs of the estimated hairpin was 0.65b, which is generally constant over the range of Re = 1500–5000.

著者

Casey T. A. Sakakibara J. Thoroddsen S. T.

出版者

American Institute of Physics

雑誌

Physics of fluids (ISSN:10706631)

巻号頁・発行日

vol.25, no.2, pp.025102, 2013-02

被引用文献数

30 1

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We introduce a modified tomographic PIV technique using four high-speed videocameras and a scanning pulsed laser-volume. By rapidly illuminating adjacent subvolumesonto separate video frames, we can resolve a larger total volume of velocityvectors, while retaining good spatial resolution. We demonstrate this technique byperforming time-resolved measurements of the turbulent structure of a round jet,using up to 9 adjacent volume slices. In essence this technique resolves more velocityplanes in the depth direction by maintaining optimal particle image density andlimiting the number of ghost particles. The total measurement volumes contain between1 ×106 and 3 ×106 velocity vectors calculated from up to 1500 reconstructeddepthwise image planes, showing time-resolved evolution of the large-scale vorticalstructures for a turbulent jet of Re up to 10 000.

著者

Sakakibara Jun Machida Nobuteru

出版者

American Institute of Physics

雑誌

Physics of fluids (ISSN:10706631)

巻号頁・発行日

vol.24, no.4, pp.041702, 2012-04

被引用文献数

32 9

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We measured velocity distribution in cross sections of a fully developed turbulentpipe flow upstream and downstream of a 90◦ bend by synchronizing two sets ofa particle image velocimetry (PIV) system. Unsteady undulation of Dean vorticesformed downstream from the bend was characterized by the azimuthal position ofthe stagnation point found on the inner and outer sides of the bend. Linear stochasticestimationwas applied to capture the upstream flowfield conditioned by the azimuthallocation of the stagnation point downstream from the bend. When the inner-sidestagnation point stayed below(above) the symmetry plane, the conditional streamwisevelocity upstream from the bend exhibited high-speed streaks extended in a quasistreamwisedirection on the outer side of the curvature above (below) the symmetryplane.