Response of a spatially developing turbulent boundary layer to a spanwise oscillating electromagnetic force

Abstract

Direct numerical simulations were performed to investigate the physics of a spatially developing turbulent boundary layer flow subjected to a spanwise oscillating electromagnetic force. The electromagnetic force was applied beneath a finite length of the flat plate. A fully implicit fractional step method was employed to simulate the flow. The mean and turbulent flow properties were obtained to analyze the spatial evolution of the near-wall vortical structure. It was found that the skin friction drag is significantly reduced for an oscillation period of T+ = 100. Imposition of electromagnetic forcing leads to a decrease in turbulence production, which in turn causes a reduction in the turbulent kinetic energy. Instantaneous flow visualization techniques were used to observe the responses of the streamwise vortices and streak structures. The visualization results show that imposition of the spanwise oscillation suppresses and weakers the streak structures. Downstream of the region where the electromagnetic force is applied the flow eventually relaxes back to a two-dimensional equilibrium boundary layer.