Experimental Investigation on Receptivity of Crossflow Instability to Discrete Roughness Amplitude and Location

An experimental parametric study of the effect of discrete roughness elements (DRE) on the development and breakdown of stationary crossflow instability on a swept wing is presented. A systematic investigation of the receptivity to various elements height and chord locations is carried out in a crossflow dominated flow. The flow is globally and locally investigated through simultaneous infra-red (IR) and planar particle image velocimetry (PIV) acquisitions that correlate the extracted transition location and the developing flow feature with the applied forcing configuration, providing insights on the physical mechanisms governing receptivity. The presented results show how a downstream shift in the DRE array location is accompanied by a transition delay, while an increase of the elements height leads to a transition advancement. Moreover, the entire set of PIV measurements allows to compare the instabilities development between different forcing cases, providing insights on the dominant physical mechanisms governing receptivity of stationary CFI to discrete roughness and possible scaling rules. In fact, an up-scaled forcing configuration replicating the instabilities strength and evolution would allow to investigate the near-flow features in a set-up easier to measure experimentally.