Evolution of Reynolds stresses in a turbulent boundary layer

Understanding Reynolds shear-stress events in a turbulent boundary layer is of crucial importance for modelling and controlling turbulent wall-flows. In this study, we examine the evolution in time and space of these shear-stress events by performing time-resolved PIV measurements in a stream-wise wall-normal plane of a turbulent boundary layer at $Re_\tau\approx2500$. The conditions are similar to the experiment by Dennis \& Nickels (J. Fluid Mech. 2011, vol. 673), who performed measurements at $Re_\theta=4700$. Four high-speed cameras positioned next to each other, 4-5 m downstream of a glass rod trip, captured a region of flow spanning approximately $2\delta$ in stream-wise and $0.5\delta$ in wall-normal direction. This zoomed-in field-of-view enables high spatial, $l^+\approx20$, and temporal resolution, $\Delta t^+\approx 1$ which will allow us to describe the evolution of shear-stress events in time and space. In the talk, detailed analyses including instantaneous tracking of Reynolds shear-stress events, quadrant decomposition and spectra of the stream-wise, wall-normal and Reynolds shear-stress fluctuations will be presented.