Experimental investigation of hypersonic boundary layer transition on a flat plate at Mach 5.2 flow using piezoelectric pressure sensors and temperature-sensitive paint

Boundary layer transition (BLT) is a serious problem in super- and hypersonic flights because the huge temperature increment happening locally on the surface of vehicles is fatal to them. Therefore, an accurate estimation of the location of BLT and the heat transfer near the BLT region is required. In this study, hypersonic boundary layer transition was observed on a flat plate using a shock tunnel facility which generates a Mach 5.2 flow. The pressure fluctuation and the heat flux distribution on the flat plate were obtained using piezoelectric fast-response pressure sensors and temperature-sensitive paint (TSP) technique. The result of the frequency analysis of the signals obtained from the pressure sensors indicated the power spectral density (PSD) between f = 60 kHz and f = 250 kHz was enhanced between x = 140 mm and x= 180 mm from the leading edge. The time-averaged heat flux distribution obtained from the TSP measurement showed that the heat flux started increasing near x = 150 mm from the leading edge of the flat plate. These results show that the boundary layer on the flat plate started transitioning from laminar to turbulent between x = 140 mm and x= 180 mm in this experiment.