Experimental study on hypersonic conical boundary layer flow under microstructure-seepage

Seepage through microstructure on the surface, as a novel approach for boundary layer flow control, holds considerable promise for drag and thermal reduction in hypersonic vehicles. This paper presents an experimental study conducted in a Mach 6 hypersonic high-temperature wind tunnel, utilizing a cone with seepage through microstructure on the surface. The study employs schlieren, high-frequency fluctuating pressure measurement techniques, and infrared thermometry. It focuses on the influence of the amplitude-frequency characteristics of the second-mode waves within the hypersonic boundary layer on aerodynamic heating on the wall. According to the research, the following findings were observed: For smooth surfaces, the characteristic frequency of the second-mode wave decreases from 109 to 87 kHz along the flow direction. However, microstructures cause an average increase in the characteristic frequency by approximately 20 kHz, while seepage causes the characteristic frequency along the flow direction to change little. Under the same seepage flow rate, the amplitude of the second-mode waves within the boundary layer exhibits two peaks along the flow direction. When the second-mode wave reaches the first peak, the wall temperature rise also peaks at the same location, indicating a synchronous increase and decrease between the second-mode waves and wall temperature rise during this stage. Under different seepage flow rates, the downstream wall with microstructure-seepage experiences the lowest temperature rise when F = 0.019 19% which may be attributed to the formation of small vortices within the microstructures by the seepage.