Experimental study of the early evolution of traveling crossflow instability on a 75° swept flat plate at Mach 6

The early evolution of the traveling crossflow instability on a flat plate with a sweep angle of 75° is experimentally investigated. The experiments are conducted in a Mach 6 quiet wind tunnel through the nano-tracer-based planar laser scattering (NPLS) technique under the unit Reynolds number of 3.45 × 106 m−1. The spanwise and streamwise structures of the traveling crossflow waves are captured, and the wavelength and frequency characteristics of the traveling crossflow waves are quantitatively analyzed based on wavelet analysis. The results show that with the increase in z-coordinate and x-coordinate, the distribution range of the traveling crossflow waves in y-direction expands, the amplitude of disturbance waves increases, and saturated crossflow wave structures appear gradually. The wavelength of the crossflow waves is about 24 mm and does not change much in different positions. In addition, the propagation velocity of the crossflow waves along the x-direction at the position of x = 130 mm and z = 60 mm is quantitatively calculated, U = 303 m/s. Thus, the characteristic frequency of the crossflow waves obtained from the NPLS image is f≈12 kHz, close to 9.57 kHz measured by Kulite at the same position.