Compressibility Effects on Flow Asymmetry over a Slender Body at High Incidence

Slender bodies of revolution at high angles of incidence produce asymmetric vortices, leading to large side forces and yaw moments even in symmetrical flight conditions. This study examines the flow past a conical forebody at different angles of attack at various Mach numbers from subsonic to supersonic flow conditions. Experiments were conducted at the FCAAP polysonic wind tunnel using a six-component strain gauge balance for force measurements, shadowgraph imaging, global pressure mapping with pressure-sensitive paint, and velocity field using particle image velocimetry. The results at subsonic speeds show that, with an increase in the angle of incidence, counter-rotating vortices develop asymmetrically over the forebody, resulting in side forces. Unlike previous literature, the variation of the maximum side force coefficient with Mach number is non-monotonic. At high supersonic speeds, both side force and vortex strength diminish significantly regardless of an increase in the angle of attack. This study demonstrates the need to decouple the Mach and Reynolds number effects to determine the nature and magnitude of vortex asymmetry. Current findings strongly suggest that compressibility has a crucial effect on crossflow shear layer development that determines the overall flow asymmetry and the strength of side forces generated at high angles of incidence.