Wall Pressure Signature in Compressible Turbulent Boundary Layers

Abstract

Large-scale turbulent flow structures associated with positive and negative wall pressure fluctuations in a compressible turbulent boundary layer are investigated. Experiments are conducted in a closed-loop transonic wind tunnel at $\mathrm{Ma} = 0.5$–0.8, Re$_\tau = 5{,}100$–9, 500 with combined velocity field and wall pressure measurements. Both, velocity and pressure statistics are analysed and compare well with existing low Mach number data. Spatial two-point correlation is applied to determine the size and orientation of the large-scale flow structures, which depending on the wall height have an averaged length scales of 4–6 $\delta$ and a maximum inclination angel of ${\approx }12^\circ$–$13^\circ$. The wall pressure fluctuations are associated with shear layer structures and it is shown that positive pressure fluctuations are correlated with low speed large-scale flow structures over streamwise extents of 4–5 $\delta$.