A hybrid prediction model for transitional separated flows over rough walls

It is known that boundary layer transition and turbulent separation flow after transition can be influenced significantly by surface roughness. Because the traditional hybrid Reynolds-averaged-Navier-Stokes (RANS)/large eddy simulation method cannot predict the boundary layer transition, and the RANS-based transition model cannot accurately simulate the massively separated flow, the present study sought to build an effective modeling strategy for the laminar, roughness-induced-transition and attached turbulence/massively separated flows that couple the very-large-eddy-simulation model and a transition model considering roughness effects. This new hybrid model was examined in the cases of the separated flat plate and the rough cylinder. Our analysis shows that the new hybrid model operates in these transitional separated flows over smooth and rough walls. Compared with the results of other classical methods, the present results are more consistent with the measured data. Furthermore, the "drag crisis"phenomenon of the cylinder is accurately simulated by the present model.