Flow Separation Behind a Bulge in Rotating Turbulent Channel Flows

In a channel rotating about the spanwise axis, the turbulence near the wall where the mean vorticity has the opposite sign of the rotation may be either de-stabilized or stabilized; the other side tends to become more stable or even relaminarized. The response of a flow separation induced by a protuberance on one of the walls of an otherwise planar turbulent channel is investigated using DNS. The bulk Reynolds number of the channel is 2,500. The bump is placed on either the stable or unstable side of the channel, modeled using an immersed boundary method. Two rotating rates ($Ro_b=2\Omega\delta/U_{b}$ = 0.42 and 1.0) were used to compared with the non-rotating baseline case. When the bulge is placed on the unstable side, rotation reduces the size of the mean separation region. At the high Rotation number, the separation is nearly completely suppressed. When the bulge is placed on the stable side, the quasi-laminar boundary layer separates earlier behind the bump and forms more coherent 2D roller vortices in the separated shear layer. The mean separation bubble reattaches much later compared with the non-rotating case. The effects of the Coriolis force on the separating shear layer will be discussed.