Studies on Effects of Periodic Wake Passing upon a Blade Leading Edge Separation Bubble : Suppresion of Separation Bubble Due to Wake Passing

This paper describes an experimental investigation on aerodynamic interaction between incoming periodic wakes from moving bars and separation bubble on a scaled leading edge model. Numerical simulations are also attempted to grasp an idea how the incoming wakes interact with the separation bubble. The model, which consists of a semi-circular leading edge and two flat-plates, is used to simulate the flow field around a compressor or a turbine blade. Cylindrical bars of the wake generator produce the periodic wakes in front of the test model. The study aims at enriching the knowledge on how and to what extent the periodic wake passing suppresses the leading edge separation bubble. Special attention is paid to emergence of wake-induced turbulent spots and subsequent calmed regions. Hot-wire probe measurements are executed under five different flow conditions to examine effects of Reynolds number, Strouhal number, direction of the bar movement and incidence of the test model against the incoming flow. The measurements reveal that the wake moving over the separation bubble does not directly suppress the separation bubble. Instead, wake-induced turbulence spots and the subsequent calmed regions have dominant impacts on the separation bubble suppression for the all test cases.