Transition in an infinite swept-wing boundary layer subject to surface roughness and free-stream turbulence

The instability of an incompressible boundary-layer flow over infinite swept wing in the presence disc-type roughness elements and free-stream turbulence (FST) has been investigated by means direct numerical simulations. Our study corresponds to experiments Örlü et al. ( Tech. Rep. , KTH Royal Institute Technology, 2021, http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-291874 ). Here, different dimensions levels FST have considered. aim present work is investigate experimentally observed sensitivity transition intensity. In absence FST, behind with a height above certain value immediately undergoes turbulence. Impulse–response analyses steady performed identify mechanism instability. For subcritical roughness, generated wave packet experiences weak transient growth then its amplitude decays as it advected out computational domain. supercritical case, which transitions turbulence, expected exhibits absolute found significant impact on particular case height. corresponding Reynolds number $Re_{hh}=461$ reaches laminar state, while very low intensity $Tu =0.03\,\%$ causes appearance spots wake roughness. These randomly are higher level $Tu=0.3\,\%$ turbulent clearly visible element, similar that for globally unstable case. presented results confirm experimental observations explain mechanisms laminar–turbulent FST.