The effect of rotation on flow separation behind a bump in turbulent channel flows

A spanwise-rotating turbulent channel with a bump on the bottom wall is studied via direct numerical simulation. The objective is to understand how the Coriolis force modulates the geometry-induced separation. The parabolic bump is 0.25H high. The mild curvature at the crest removes fixed point separation, allowing investigation of separation onset. Counter-clockwise (+) or clockwise (-) rotation is applied at rotation number Ro_b = 2ΩH/U_b of 0, ±0.42, and ±1.0. A constant mass flow rate is maintained among all cases corresponding to Re_b = HU_b/ν = 2500. Compared to the non-rotating flow, separation is delayed and reattachment occurs earlier when Ro_b > 0, reducing the mean recirculation region by up to 94% at the highest rotation rate. The delayed onset of separation is attributed to enhanced turbulence due to the Coriolis force, despite the mean momentum deficit at the crest of the bump is more significant than it in the non-rotating case. When Ro_b < 0 separation of the relaminarized flow occurs closer to the crest and the separated shear layer is stable until rolling into spanwise vortices approximately eight bump heights downstream. A lower form drag is correlated with reduced separation when Ro_b > 0, though not when Ro_b < 0. The total drag, including the friction drag over the flat walls, is lower for all rotation cases.