Experimental investigation of the unsteady structure of a transitional plane wall jet |
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Authors: | S Gogineni C Shih |
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Institution: | (1) Systems Research Laboratories 2800 Indian Ripple Road Dayton, OH 45440-3696, USA, IN;(2) FAMU-FSU College of Engineering Florida A&M and Florida State Universities Tallahassee, FL 32310, USA, US |
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Abstract: | A laminar wall jet undergoing transition is investigated using the particle image velocimetry (PIV) technique. The plane
wall jet is issued from a rectangular channel, with the jet-exit velocity profile being parabolic. The Reynolds number, based
on the exit mean velocity and the channel width, is 1450. To aid the understanding of the global flow features, laser-sheet/smoke
flow visualizations are performed along streamwise, spanwise, and cross-stream directions. Surface pressure measurements are
made to correlate the instantaneous vorticity distribution with the surface pressure fluctuations. The instantaneous velocity
and vorticity field measurements provide the basis for understanding the formation of the inner-region vortex and the subsequent
interactions between the outer-region (free-shear-layer region) and inner-region (boundary-layer region) vortical structures.
Results show that under the influence of the free-shear-layer vortex, the local boundary layer becomes detached from the surface
and inviscidly unstable, and a vortex is formed in the inner region. Once this vortex has formed, the free-shear-layer vortex
and the inner-region vortex form a vortex couple and convect downstream. The mutual interactions between these inner- and
outer-region vortical structures dominate the transition process. Farther downstream, the emergence of the three-dimensional
structure in the free shear layer initiates complete breakdown of the flow.
Received: 8 November 1995/Accepted: 6 November 1996 |
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