The Interaction of a Swept-Wing Boundary Layer with Surface Excrescences

摘要

The influence of steps and gaps on swept-wing crossflow development is an emerging area of interest. An experiment is performed on a 40° swept-wing model in a facility with a turbulence level of 0.10%. Periodic discrete roughness elements are spaced at the critical crossflow wavelength and used to excite the crossflow disturbance. The subsequent interaction with a two-dimensional roughness strip of various height and chordwise location is investigated. Naphthalene flow visualisation is used to help understand the global transition features, whilst detailed boundary layer measurements are conducted using hot-wire anemometry. Excrescences located closest to the neutral point are seen to have the biggest influence on stationary-crossflow disturbance amplitude. There appears to be a threshold height below which the excrescence has no significant influence on the boundary layer development. Excrescences located further downstream appear to generate greater unsteadiness in the boundary layer for a given excrescence height, leading to earlier transition.