Wall pressure signature in compressible turbulent boundary layers

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 Ma = 0.5 - 0.8, Ret=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 δ and a maximum inclination angel of ≈ 12o - 13o . 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 structure over streamwise extents of 4 - 5 δ