Modelling the effect of flow pulsation on turbulen flow in a 10-deg plane diffuser.

Flows involving detachment and reattachment are found in a range of engineering systems such as vehicles and planes. The 10o diffuser flow considered here sees grad- ual change in the mean flow, which makes it challenging to model. The separation point here is not geometrically fixed, so the effect of separation control can then be investigated for both the flow detachment and reattachment processes. The subject of this investigation is the response of the flow to the imposed unsteadiness arising from a periodic injection / suction upstream of the reattachment point. The test case examined is that studied experimentally by Masuda et al.1 shown in Figure 1. There are considerable modelling challenges in computing flows exhibiting even steady detachment and reattachment. In order to minimiz computing times there is a desire to employ relatively simple RANS models of turbulence. However, simple linear eddy- viscosity models are known to perform badly in separate flows, and even non-linear eddy- viscosity models do not all produce accurate and reliable results. In a recent study, Craft et al.2 introduced refinements to a non-linear eddy-viscosity model and showed that this performed quite successfully in predicting the steady flow and heat transfer through a sudden pipe expansion. The present work tests the two-equation linear k − epsilin schemes, and the modified two-equation non-linear model.