Effects of Curvature on Mack Mode Evolution in Hypersonic Boundary Layer

The aerodynamic performance of hypersonic vehicles is strongly influenced by the boundary layer transition. The prediction of boundary layer transition is extremely challenging because transition depends on large number of parameters. Existing research has largely focused on the effects of freestream parameters on transition, such as freestream Mach number, disturbances environment, and angle of attack, etc. While the influence of wall curvature in low-speed and supersonic flows has been well-studied, its impact on the Mack mode in hypersonic flows remains insufficiently explored. Based on the linearized compressible Navier–Stokes equations, this paper parametrically investigates the effect of curvature on the Mack mode evolution in hypersonic boundary layers of flat-plate, concave, and convex curvatures. The results indicate that, compared to flat plate, the favorable pressure gradient in convex curvature boundary layer stabilize Mack mode, while the adverse pressure gradient in concave curvature boundary layer destabilize Mack mode. As the curvature increases, for convex surface, the favorable pressure gradient becomes pronounced and Mack mode is suppressed; while for concave surface, the adverse pressure gradient becomes enhanced and Mack mode is amplified. The study provides guidance for the transition design of hypersonic configurations.