Three-Dimensional Receptivity of Hypersonic Boundary Layers over Sharp Wings

The transition from laminar to turbulent flow in hypersonic boundary layers is essential for the design of high-speed aircraft, as it significantly increases local heating loads. The receptivity process, which acts as the origin of unstable modes and leads to the final breakdown in low-disturbance environments [Fedorov 2011], is of great importance. Due to the high growth rates in hypersonic flows, the second Mack mode has garnered considerable attention [Balakumar 2015]. Second Mack modes, as described by Fedorov and Khokhlov [Fedorov and Khokhlov 2001], are generated by the synchronization between mode F and mode S. Recent research indicates that lower-frequency disturbances, such as first Mack modes [Chen et al. 2017, Guo et al. 2023] and crossflow modes [Wan et al. 2021, Qiu et al. 2024], are also critical for transition. Zhu et al. [Zhu et al. 2021] found that the soliton-like wave packet, which plays a determining role in turbulence production, arises from the vortical first Mack mode rather than the rapidly growing dilatational second Mack mode. Similarly, according to Qiu et al. [Qiu et al. 2024], traveling crossflow vortices are essential for the formation of low-frequency hairpin-like structures that ultimately trigger turbulence. In low-frequency regimes, fast modes can be neutral in the boundary layer, preventing the synchronization between F modes and vortical or S modes [Fedorov and Tumin 2011]. The receptivity process can vary considerably from that in high-frequency regimes. However, the understanding of the receptivity process for these two modes remains limited. In the current research, the receptivity process of the hypersonic boundary layer over a sharp wing to three-dimensional (3D) freestream planar slow acoustic and vorticity waves will be analyzed in detail. The sweep angle will be varied to observe the response of hypersonic boundary layers.