Application of pressure-sensitive paint to investigate hypersonic shock-wave/boundary-layer interactions

Surface pressure distributions of a hypersonic shock-wave/boundary-layer interaction have been investigated at an average $Re=28.2\times 10^6{m}^{-1}$ in the Mach 7.2 Wind Tunnel facility located at the University of Texas at San Antonio. A ruthenium-based fast-responding pressure-sensitive paint, made in-house, was applied to a canonical wall-to-wall flat plate with a 33° compression ramp. A static calibration of the paint’s response was used to extract global surface pressure measurements of the hypersonic shock-wave/boundary-layer interaction. The 33° ramp experienced high-pressure regions and “Görtler-like” vortices were observed with a spacing of 3 – 6 ${\delta }_{99}$. The vortex structure spacing was further investigated using surface oil flow visualization, giving a spacing of 2 – 4 ${\delta }_{99}$. The separation region showed lower pressures than the ramp, and the lowest pressures recorded appeared from the leading edge of the model to the separation region. In this study, a statistical and spectral analysis of the images was performed globally and at discrete locations along the model. The spectral analysis showed energy peaks on the ramp over a low-frequency band of Strouhal numbers between $S{t}_{\delta }$ 0.00029 – 0.00147. Modal analysis was also performed to further examine the energy content of the structures and sub-structures that appeared on the compression ramp.