Opposition Control of Turbulent Taylor-Couette Flow

Direct numerical simulations (DNS) of an opposition-controlled turbulent Taylor-Couette (TC) flow is performed. Opposition control is then applied. Significant drag reduction is achieved by opposition control and the skin friction drag is decreased up to 31% with the wall-normal control. Strong modifications of the turbulence statistics in the near-wall region are observed. The streamwise velocity fluctuation is greatly reduced and shows a more symmetric profile. The origin of the boundary layers seems to undergo a displacement toward the middle of the flow. Besides, the visualization of the coherent flow structures shows a significant reduction of their number when the control is applied. In a further step, the combination of wall-normal and spanwise control, as well as the influence of the gain on the input response are investigated. The efficiency of this control strategy is then compared with the opposition control.