Visualization of supersonic flow over double wedge

Flow visualization of supersonic flow over a double ramp is achieved by the nano-tracer planar laser scattering (NPLS) technique in a supersonic low noise wind tunnel at Mach number 3.0. The fine structures of the boundary layer on the model, as well as the temporal and spatial evolutionary characteristics of the coherent structures, are revealed and investigated. High-spatiotemporal resolution images of the incoming boundary layer with laminar flow over the model are presented. Boundary layer transition occurs at the first ramp and the boundary layer at the second ramp has already been turbulent flow. The hairpin vortex and hairpin packet can be observed at the boundary layer of the first ramp. The angles of the hairpin vortex and hairpin packet are larger than that in a flat-plate because of adverse pressure gradient of the ramp. NPLS images of the incoming boundary layer with turbulent flow over the model are shown. The coherent structures at the first ramp are similar to the incoming boundary layer, which exhibit an obvious hierarchy. In contrast, the coherent structures at the second ramp exhibit different characteristics.