Reynolds-Number Effects of Separating Flow over a Bump in Spanwise Rotating Channels

Direct numerical simulations of turbulent channel flow rotating about the spanwise axis are performed at three Reynolds numbers. A parabolic bump is placed either on the anti-cyclonic or cyclonic wall of the channel and generates pressure-induced flow separation on its lee side. Reduced mean separation region is observed when the flow over the bump is unstabilized by the Coriolis force and/or at higher Re. The total drag decreases with rotation regardless of the rotation direction for this configuration. The form drag produced by the separated flow does not vary significantly with rotation or Re, indicating an inviscid-dominant drag production mechanism and the disadvantage of utilizing the extent of the separation region as an indicator of the magnitude of the form drag. The separated shear layer deviates from the canonical one due to the interactions of various types of vortices and the energy redistribution between Reynolds stresses.