Differential Interferometric Measurement of Instability in a Hypervelocity Boundary Layer

The prediction of laminar–turbulent transition location in high-speed boundary layers is critical to hypersonic vehicle design because of the weight implications of increased skin friction and surface heating rate after transition. Current work in T5 (the California Institute of Technology’s free piston reflected shock tunnel) includes the study of problems relevant to hypervelocity boundary layer transition on cold-wall slender bodies. With the ability to ground-test hypervelocity flows, the study of energy exchange between the boundary layer instability and the internal energy of the fluid is emphasized. The most unstable mode on a cold-wall slender body at zero angle of incidence is not the viscous instability (as in low-speed boundary layers) but the acoustic instability. Quantitative characterization of this disturbance is paramount to the development of transition location-prediction tools