Receptivity of a hypersonic flow over a blunt wedge to a slow acoustic wave

The receptivity of the second mode for Mach 6 flow over a blunt wedge with a nose radius of 0.258mm is investigated numerically. When a plane slow acoustic wave is imposed on the freestream, the receptivity process of the boundary layer goes through three stages, with the development of an entropy-layer mode, a fast mode, and nonmodal external disturbances, before exciting the second mode. The first two dominant modes can be obtained by linear stability theory in the entropy layer and the boundary layer, respectively, whereas the third is a complicated type of disturbance whose shape function peaks in the entropy layer. The results show that the nonmodal disturbances in the entropy layer play a leading role in the excitation of the second mode, which suggests that the growth of nonmodal disturbances could dominate nonmodal amplification, eventually leading to boundary-layer transition. Published under an exclusive license by AIP Publishing.