The impact of three-dimensional compression on supersonic boundary layers

By using vertically intersecting double wedges, the effect of three-dimensional compression on a supersonic boundary layer transition and turbulent characteristics is experimentally investigated by means of nanoparticle-based planar laser scattering and particle image velocimetry techniques. The structural and statistical responses of the supersonic boundary layer to an additional spanwise compression are compared with those subjected to streamwise compression alone. Studies demonstrate that three-dimensional compression can induce transverse instability, which accelerates boundary layer transition and reduces the transition distance. For turbulent inflow, the flow velocity within the boundary layer is evidently slowed down, leading to the formation of a bulge of the boundary layer. The turbulence fluctuation is significantly strengthened by the side compression, which breaks the large-scale structures into smaller ones. Further downstream of the disturbing region, the turbulence gradually recovers. Through spatial correlation, it is found that the side compression tends to make less correlated structures both in streamwise and wall-normal directions.