High-resolution measurements of two-dimensional instabilities and turbulence transition in plane mixing layers |
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Authors: | J Estevadeordal S J Kleis |
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Institution: | (1) Innovative Scientific Solutions, Inc. 2766 Indian Ripple Rd. Dayton, OH 45440-3638, USA, IN;(2) Department of Mechanical Engineering University of Houston Houston, TX 77204-4792, USA, US |
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Abstract: | High-resolution two-dimensional (2D) measurements on a large plane mixing layer provide new quantitative information of its
spatial and temporal evolution to turbulence. Periodic acoustic excitation with three frequencies was used to stabilize the
fundamental instability of the mixing layer (roll-up) and its first and second subharmonics (vortex pairings). Phase-locked
velocity measurements of the time evolution in 2D space (x, y, t) reveal accurate spatially resolved primary (2D) instabilities of the mixing layer and turbulence transition. The measurements
unveil new quantitative details of the initial Kelvin–Helmholtz waves and their spatial and temporal evolution into vortex
shedding and the effect of the second subharmonic on the first vortex pairing. The second-subharmonic effect hastens alternate
first pairings of the rollers, with the result that pairing is completed at two downstream locations. The pairings that occur
closer to the knife-edge are more organized (laminar) than those occurring farther downstream (transitional). This effect
is corroborated using Taylor’s hypothesis to compute the vorticity distributions from the measured velocity field and a pseudo-spectral
simulation of the temporal evolution of the mixing layer.
Received: 26 March 1998/Accepted: 2 March 1999 |
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