Influence of upstream flow characteristics on the reattachment phenomenon in shallow cavities

Abstract

The influence of the upstream flow characteristics on the behaviour of the flow over a shallow cavity and on the reattachment phenomenon is examined. Accord- ingly, a comparison of the cavity's flow structure is performed for two different upstream flows: the wall jet flow and the boundary layer flow. The wall jet pos- sesses a particular structure with two regions: an inner layer analogous to that of a boundary layer and an outer layer similar to that of a free jet; this layer is an additional source of turbulence production in addition to that of the inner shear layer. The present study interested to the effect of this external layer on the shal- low cavity's flow. The numerical approach is based on the low Reynolds stress omega turbulence model. Fluent 6.3 and the pre-processor Gambit 2.3 are used for the computation. The numerical results indicate that the flow structure is very sensitive to the upstream flow's characteristics. Indeed, for the same Reynolds number and the same boundary layer thickness at the cavity leading edge, the cavity flow structure in a wall jet upstream flow case differs considerably from that of a boundary layer upstream flow. The most important finding is the earlier reattachment process in the wall jet inflow case, where an important reduction of the reattachment length is observed compared to that of a cavity under a bound- ary layer flow.