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Effect of Mach number on the structure of turbulent spots

Published online by Cambridge University Press:  05 October 2006

L. KRISHNAN
Affiliation:
Aeronautics and Astronautics, School of Engineering Sciences, University of Southampton, SO17 1BJ, UK
N. D. SANDHAM
Affiliation:
Aeronautics and Astronautics, School of Engineering Sciences, University of Southampton, SO17 1BJ, UK

Abstract

Direct numerical simulations have been performed to study the dynamics of isolated turbulent spots in compressible isothermal-wall boundary layers. Results of a bypass transition scenario at Mach 2, 4 and 6 are presented. At all Mach numbers the evolved spots have a leading-edge overhang, followed by a turbulent core and a calmed region at the rear interface. The spots have an upstream-pointing arrowhead shape when visualized by near-wall slices, but a downstream-pointing arrowhead in slices away from the wall. The lateral spreading of the spot decreases substantially with the Mach number, consistent with a growth mechanism based on the instability of lateral shear layers. Evidence for a supersonic (Mack) mode substructure is found in the Mach 6 case, where coherent spanwise structures are observed under the spot overhang region.

Type
Papers
Copyright
© 2006 Cambridge University Press

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