Краткое описание

The effects of a spanwise rotation on the channel flow across a sudden expansion are investigated using DNS. Four rotation regimes are considered with the same Reynolds number Re = 5000 and ratio expansion Er = 1.5. Upstream from the expansion, inflow turbulent conditions are generated realistically for each rotation rate through a very simple and efficient technique of recycling without the need of any precursor calculation. As the rotation is increased, the flow becomes progressively asymmetric with stabilization/ destabilization effects on the cyclonic/anticyclonic sides respectively. These rotation effects, already present in the upstream channel consistently with previous studies, lead further downstream to a reduction/increase of the separation size behind the anticyclonic/cyclonic step. In the cyclonic separation, the free-shear layer created behind the step corner leads to the formation of large-scale spanwise vortices that are found more and more 2D as the rotation is increased. Conversely, in the anticyclonic region, the turbulent structures in the separated layer are more 3D and also more active to promote the reattachment. In the present flow configuration where Coriolis forces do not work while being passive on a purely 2D dynamics, the phenomenological model of absolute vortex stretching is useful to understand how the rotation influences the flow dynamics.