Travelling and Stationary Crossflow Instability and Control Experiments Involving a Swept Fin-Cone Model in Mach 6 Flow*

The harshness of the hypersonic environment presents numerous technical challenges. The stability of the boundary layer over a vehicle in this regime is still a major issue in flight vehicle design. If the boundary layer becomes turbulent, aerothermodynamic heating and viscous effects such as skin friction dramatically increase. One method that a 3-D boundary layer may become turbulent is through an inviscid mechanism known as the crossflow instability. The crossflow instability has been well studied at subsonic speeds, but comparatively few crossflow experiments have been done in hypersonic flow. Even fewer hypersonic crossflow studies have been conducted where explicit attempts at influencing the location of boundary layer transition (flow control) have been made.

This work pertains to the stability of a 3-D boundary layer over a swept fin-cone model in Mach 6 flow. The cone nose tip bluntness and freestream Reynolds number were varied, and their effects on boundary layer transition and heating were observed. The focus of the experiments has been on the highly-swept fin where both stationary and travelling crossflow modes have been identified. Infrared Thermography was used to analyze the stationary mode and high-frequency pressure measurements were taken to analyze the travelling mode.

Attempts at flow control were also made to increase the laminar flow region over the fin. This involved placing discrete roughness elements (DREs) near the leading edge of the fin to promote a less amplified stationary instability mode. Notable delay in the onset of boundary layer transition was observed in a particular experimental configuration. The spectral content of the stationary mode has been compared to companion computational studies performed by Peck et al. at the Texas A&M Computational Stability and Transition Laboratory and agreement between experiments and computations has been found.