Direct numerical simulation of a shear driven three-dimensional turbulent boundary layer

Direct numerical simulations have been carried out in a flat-plate turbulent boundary layer with an impulsive spanwise velocity at the wall, thus yielding a skewed three-dimensional turbulent boundary layer (3DTBL). Particular attention is given to the effects of cross flow and Reynolds number. The present inlet Reynolds number is equal to momentum thickness Reynolds number Re_θ=300, 600 and 900. The latter Re_θ is close to that of Kannepalli and Piomelli (2000) who performed the wall-resolved large eddy simulation at Re_θ≈1100. After imposing cross flow, a decrease in magnitude is observed for the turbulent kinetic energy, associated with the behavior that the shear stress lags in change behind the strain rate. In a near equilibrium 3DTBL, the spanwise Reynolds stress ⟨vw⟩ and the Reynolds shear stress ⟨uv⟩ become more and less energetic with increasing cross flow. A large magnitude of cross flow leads to not only short streamwise extent of streaks but also clustering of vortical structures, where the wall pressure fluctuation also shows a large-scale pattern. In the recovery region, a significant Re effect is found for the streamwise skin friction coefficient, but not for the spanwise skin friction one. In this region, the recovery to the zero-pressure-gradient state is also slow.