Experimental Investigation of the Hypersonic Boundary Layer Transition on a 45° Swept Flat Plate

In this paper, the experimental study on the transition process of a boundary layer on a 45° swept flat plate is performed in the Mach 6.0 hypersonic low-noise wind tunnel. The instantaneous fine structures of the boundary layer on the swept flat plate in streamwise and spanwise planes have been investigated based on the Nano-tracer Planar Laser Scattering (NPLS) technique, respectively. The spatiotemporal evolution characteristics of the boundary layer translating from laminar to turbulence are analyzed. The transition process from laminar to turbulent flow is shown, and its spatiotemporal evolution characteristics are analyzed. It is found that the transitional plane is parallel to the leading edge of the 45° swept flat plate under the unit Reynolds number of 1.67 × 107 m–1. The distance from the turbulent zone to the leading edge of the swept flat plate is 18.9R. The laminar strip is at an angle of 9° to the streamwise plane. Using Temperature-Sensitive Paints (TSP) technique, the temperature gradient distribution on the surface of the 45° swept flat plate wall was obtained, and the boundary layer transition regular pattern obtained by temperature gradient was agree with the coherent structures obtained from the NPLS images. Compared the TSP result with the NPLS images, the correlation between flow structure and wall temperature gradient was obtained.