Estimation of large scale motions in a turbulent boundary layer from direct wall shear stress measurements*

Direct measurements of the fluctuating wall shear stress are captured in a zero pressure gradient turbulent boundary layer at Re_θ ≈ 5000 with a 1 mm × 0.2 mm floating element capacitive sensing system. The velocity field is captured simultaneously in separate stereo particle image velocimetry (PIV) data planes, and the estimated velocity field is created based on correlations with targeted wall shear stress events. These events are characterized by instantaneous wall shear stress magnitude, local turbulence intensity via VITA-type approaches, and large scale patterns via low pass filtering. The estimated field is compared to the time-resolved hot-wire measurements of single point velocity to ascertain the effects of the frozen field hypothesis at this Reynolds number, using previous measurements of the convection velocity of the wall shear stress. In addition, the comparison between the spatial- and temporal- reconstruction is used to capture incipient attached eddy scaling at this Reynolds number.