NUMERICAL STUDY OF FLOW CONTROL IN A DIFFUSER BY VIBRATION WALL AND MECHANISM ANALYSIS BY ESTABLISHMENT OF A NONLINEAR SIMPLIFIED MODEL

摘要

Vibration wall is a kind of important active flow control method, while the interaction between the vibration wall and unsteady separation flow is so complex for researchers to discover the corresponding mechanism. Current researches imply that the better controlled flow is the more ordered flow. At first, the effect of the different control parameters of vibration wall on the total pressure loss was studied by numerical simulation to reveal the control mechanism of vibration wall. Numerical results show that when the vibration frequency reaches the separation vortex frequency, with the amplitude of 0.1 characteristic length, the best flow control is resulted. Furthermore, it can be seen that, the vibration wall with effective parameters can make the large-scale vortices more dominant, while small-scales ones(or clutters) appear less in the pattern. This observation indicates that the flow field tends to be more orderly. Moreover, to further explain this ordering mechanism, a simplified model is established and analyzed, showing that valid external excitement can strengthen the dominated frequency of K-H wave which forms the large-scale separation vortices, and restrains small-scale ones. The flow field is then more orderly and less chaotic, resulting in reduction of flow loss.