DNS Study on Turbulent Transition Induced by an Interaction between Freestream Turbulence and Cylindrical Roughness in Swept Flat-Plate Boundary Layer

Laminar-to-turbulent transition in a swept flat-plate boundary layer is caused by the breakdown of crossflow vortex via high-frequency secondary instability and promoted wall-surface roughness freestream turbulence (FST). Although FST characterized its intensity wavelength, it not clear how wavelength affects turbulent transitions interacts with roughness-induced transition. The depends on wind tunnel or in-flight conditions, arbitrary control practically difficult experiments. By means direct numerical simulation, we performed parametric study interaction between disturbance Falkner–Skan–Cooke layer. One our aims to determine critical height dependence peak FST. We found suppression promotion process as result interaction. In particular, immediate behind was delayed long-wavelength FST, where presence suppressed emanating from edge. Even below criticality, short-wavelength form hairpin triggered an early before crossflow-vortex finger vortex. Thresholds for wavelengths that promote suppress were also discussed provide important indicator prediction due and/or wing.