Turbulent oscillating channel flow subjected to a wind stress

Large eddy simulations of a periodic channel subjected to an oscillating pressure gradient and a wind stress at the free surface are presented. The resulting pulsating flow can be decomposed in a constant part which is the result of the wind stress and an oscillating part due to the pressure gradient. The pressure gradient first accelerates the flow leading to an increased wall stress and higher turbulence levels. Near the bottom a logarithmic layer is observed with strong turbulent streaks as is typical for steady boundary layer turbulence. When the flow is decelerated, streaks are weakened and smoothened by viscosity. After the flow reverses a log layer with turbulent streaks reappear when the wall stress builds up. At the free-surface the wind stress drives a constant production of turbulence and streaks are present throughout the cycle. As bottom and free-surface streaks are aligned mainly one-component turbulence is observed in the interior.