The roughness-shielding concept involves reducing the receptivity of large-amplitude discrete roughness elements (DREs) by surrounding them with subcritical distributed roughness. The present work studies the effects of distributed roughness present upstream or downstream of DREs using direct numerical simulations (DNS) and wind tunnel experiments using suitable abstractions. The roughness elements, whose shapes are chosen to enable simple, matched studies, are incorporated in the DNS using an immersed boundary method. The detailed evolution of the different components of the vorticity field is examined. The DNS is supported by naphthalene shear-stress visualization of matched experiments at the Klebanoff–Saric Wind Tunnel at Texas A&M University. Both DNS and experimental results show that placing a model-distributed roughness strip or an equivalent flat strip either only upstream or only downstream of the DRE can suppress transition. Detailed mechanisms responsible for transition control by upstream and downstream distributed roughness patches are investigated and explained from a vorticity dynamics point of view. A generalized shielding strategy using a streamwise array of spanwise strips is suggested.
Mechanisms of Roughness-Induced Boundary-Layer Transition Control by Shielding
AIAA Journal ; 58 , 7 ; 2951-2963
2020-07-01
Conference paper , Article (Journal)
Electronic Resource
English
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