Turbulent drag reduction over curved walls

Separation drag reduction through a spanwise oscillating pressure gradient

“…The distribution of the pressure difference in the separated region is qualitatively similar to that found by Banchetti et al. (2020) for a channel flow modified by a smooth bump and altered by wall travelling waves. In their flow, the total pressure sufficiently downstream of the obstacle recovers the negative constant slope behaviour proper of channel flows over smooth walls.…”

“…We do not define the drag coefficients on the left and the right bar sides and their reductions because, as remarked by Banchetti et al. (2020), it is not meaningful to define a local pressure coefficient for an incompressible flow as the pressure values can be shifted by any constant.…”

“…Banchetti et al. (2020) fixed the total pressure at the inflow location of their computational domain in order to quantify the effect of the pressure drop given by their control method. In all our cases, we instead maintain the pressure constant at the further end of our computational domain.…”

“…2019; Banchetti et al. 2020).

Figure 15.Contour plots of time- and spanwise-averaged velocity in the channel for uncontrolled ( a ) and controlled case ( b ).

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“…(2016 a ) and Brackston, Wynn & Morrison (2018) used oscillating flaps positioned at the back sides of a bluff body in a wind tunnel to control the separation wake via reduced-order feedback control. The recent numerical study of Banchetti, Luchini & Quadrio (2020) showed that streamwise travelling waves of spanwise wall velocity can reduce the pressure drag of flows separating marginally behind smooth obstacles.…”