Visualization of an Isolated Vortex Ring Generated from Step-Like Wind Variation and the Overshoot Phenomenon of Axial Velocity

The flow field of a free square jet generated from an unsteady wind tunnel with a step-like axial velocity variation was measured using an ultrasonic anemometer. Three-dimensional velocity vector fields were synthesized by computational modeling from the measured time-series velocity data. The vorti...

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Bibliographic Details
Published inJournal of Fluid Science and Technology Vol. 6; no. 4; pp. 685 - 699
Main Authors HARA, Yutaka, HIRATA, Naoya, HAYASHI, Tsutomu
Format Journal Article
LanguageEnglish
Published Tokyo The Japan Society of Mechanical Engineers 2011
Japan Science and Technology Agency
Subjects
Free Square Jet
Overshoot
Step Wind
Ultrasonic Anemometer
Unsteady Wind Tunnel
Vortex Ring
Vorticity
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Summary:The flow field of a free square jet generated from an unsteady wind tunnel with a step-like axial velocity variation was measured using an ultrasonic anemometer. Three-dimensional velocity vector fields were synthesized by computational modeling from the measured time-series velocity data. The vorticity vector field was calculated after appropriate interpolation and extrapolation. A three-dimensional geographical representation of the isosurface of the vorticity vector norm showed that an isolated vortex ring separated from the shear layer and changed its shape as it moved downstream. In order to elucidate the cause of the overshoot peak observed in time-dependent variations of the axial velocity for the step-like jet, the velocities induced at an observation point on the jet axis, first by the isolated vortex ring and then by the other unsteady portions, were calculated using Biot-Savart's Law. The contribution to the overshoot peak from the other portions, including the re-developing shear layer, was larger than that from the isolated vortex ring.
ISSN:1880-5558
1880-5558
DOI:10.1299/jfst.6.685