Direct numerical simulation is used to investigate the transition induced by three-dimensional isolated roughness elements in a supersonic boundary layer at a freestream Mach number of 3.5. Simulations are performed for two different configurations: one is a square planform roughness element, and the other is a diamond planform roughness element. The mean flow calculations show that the roughness element induces counter-rotating streamwise vortices downstream of the roughness element. These vortices persist for a long distance downstream, lift the low-momentum fluid from the near-wall region, and place it near the outer part of the boundary layer. This forms highly inflectional boundary-layer profiles. These observations agree with recent experimental observations. The receptivity calculations show that the amplitudes of the mass-flux fluctuations near the neutral point for the diamond-shaped roughness element are the same as the amplitude of the acoustic disturbances. They are three times smaller for the square-shaped roughness element.
Roughness-Induced Transition in a Supersonic Boundary Layer
AIAA Journal ; 54 , 8 ; 2322-2337
2016-08-01
Conference paper , Article (Journal)
Electronic Resource
English
Roughness-Induced Transition in a Supersonic Boundary Layer
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