Curvature-controlled instability coupling in hypersonic three-dimensional boundary-layer transition

Boundary-layer transition on hypersonic lifting bodies is strongly affected by three-dimensional effects and surface curvature, which influence instability development and aerodynamic heating. However, the specific role of curvature in modulating transition behavior remains not fully characterized. This study investigates the effect of geometric curvature on transition mechanisms using a parameterized lifting-body configuration. Variations in concave and convex curvature are introduced to examine their influence on pressure distribution, boundary-layer structure, and instability interaction. Simulations are performed using an improved k–ω–γ transition model. Results show that curvature modifies the circumferential pressure gradient and boundary-layer thickness, leading to significant changes in dominant instability modes and transition patterns. Increasing concave curvature promotes the interaction between crossflow and streamwise instabilities, resulting in a shift from single- to double-cone transition structures. Changes in convex curvature produce non-monotonic variations in transition behavior, including switching between different dominant mechanisms and corresponding transition-front shapes. These results demonstrate that geometric curvature provides an effective means of controlling transition behavior and offers practical guidance for the aerodynamic design of hypersonic vehicles.