Interaction of Taylor-Görtler and hairpin vortices during flow separation in a rotating channel flow

DNS of a spanwise-rotating turbulent channel with a bump on the bottom wall was performed to explore the rotation effects on flow separation. This configuration represents surface imperfections in turbomachinery that may degrade the performance. Simulations were performed at $Re_b$=$U_b H/\nu$= 2500. A non-rotating case was compared with counter-clockwise (+) and clockwise (-) rotating cases at rotation numbers $Ro_b=2\Omega H/U_b$= $\pm$ 0.42 and $\pm$1.0. It was observed that G\"{o}rtler vortices on the anticyclonic side of the channel dominated the three-dimensionalization of the separating shear layer. Correlations were observed between absolute vorticity ratio ($S=\Omega/\Omega_s$ where $\Omega_s$ is the mean shear rotation) thresholds of $S$= -1 and $S$= -0.5 and regions of elevated Reynolds stresses. The one-dimensional destabilization layer ($-1<S<0$) in a smooth rotating channel was enlarged to two-dimensional regions downstream of the bump, due to near-wall deceleration caused by adverse pressure gradients (APGs). On the anticyclonic side of the channel, regardless of flow separation occurrence, turbulent hairpin vortices were ejected into these regions by the G\"{o}rtler vortices. The expanded destabilization region augmented the lifted hairpin vortices, allowing them to persist longer and extract significant energy from the mean flow. This resulted in elevated turbulence far away from the wall, persisting for more than 50 bump heights downstream of the bump.