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

---

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

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

---

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.

著者

Sakakibara Jun Kita Junichiro Osato Naoyuki

出版者

American Institute of Physics

雑誌

Review of scientific instruments (ISSN:00346748)

巻号頁・発行日

vol.83, no.3, pp.036103, 2012-03

被引用文献数

15

---

We developed a video recording system with the capability of tracking moving objects and used it to track the flight of an insect. The system consists of two galvano mirrors, which redirect the light coming from the object in two orthogonal directions toward a high-speed camera to capture the image. An additional high-speed camera, which views the same object through a beam splitter placed between one of the galvano mirrors and the observation camera, detects the position of the object. The mirror angle is controlled to maintain the position of the object at the center of the view, allowing the object to be tracked. In order to validate this system, images of a live fly in flight were recorded along a flight path that was much longer than the field of view of the stationary camera. A high-resolution video image of a rapidly moving live fly was successfully captured.