Receptivity of crossflow instability to discrete roughness amplitude and location

The effect of discrete roughness elements on the development and breakdown stationary crossflow instability a swept wing is explored. Receptivity to various element heights chordwise locations explored using combination experimental theoretical tools. Forcing configurations, determined based linear stability predictions, are manufactured applied in low turbulence facility. Measurements performed infrared thermography, quantifying transition front location, planar particle image velocimetry, providing reconstruction instabilities their associated growth. corroborated with simulations nonlinear parabolised equations. Results confirm efficacy introducing conditioning instabilities. Primary amplitudes resulting laminar-turbulent location found strongly depend both amplitude location. Reynolds number height satisfactorily approximate initial forcing amplitude, revealing importance local velocity effects non-zero-pressure gradient flows. Direct estimation perturbation from suggests existence pertinent flow mechanisms vicinity, active onset modal Dedicated velocimetry planes, elucidate momentum deficit wake which rapidly decays downstream followed by mild growth, representing first evidence transient behaviour boundary layers. outcome this work identifies strong scalability dynamics warranting upscaling more accessible, measurable spatially resolved configurations future experiments.