Surface-shear-stress pulses in adverse-pressure-gradient turbulent boundary layers

Surface hot-wire evaluations of the time-dependent surface shear stress were employed to identify characteristic magnitudes and times for the pulses. It was found that large, time-dependent, surface-shear-stress pulses dominate the surface shear stress for Reynolds-number flows. Large pulses persist into the adverse pressure regions leading to intermittent separation. The minimum surface shear stress in the turbulent boundary layers appears to be limited by simple viscous decay. The timescale between pulses is a characteristic time related to the production of the surface shear stress in turbulent boundary layers.