Study of unsteady tip leakage flow characteristic in high pressure turbine stage

Three-dimensional time-dependent Reynolds averaged Navier-Stokes equations were solved to investigate the unsteady tip leakage flow in a transonic high pressure turbine stage.The changing rules of tip leakage flow as well as the reasons were indicated based on the study of the effect of stator trailing edge wake and shock waves.Results show that the outboard branch of the waves causes the periodic modification of the flow inside the tip clearance,while the stator trailing edge wake and wave make the leakage vortex changes together.The shock wave goes deep into the passage of the rotor and passes through the tip clearance periodically.When the shock wave passes the tip clearance,a strong adverse pressure gradient appears nearby the leading edge of the clearance.In addition due to the adverse pressure gradient, the separation bubble grows and a separation phenomenon appears at the forepart of the tip clearance.Meanwhile,the leakage flowmass increases and reverberates as the result of the shock wave.Because of the effect of both stator trailing edge wave and shock waves,the strength of the vortex attains to a momentary peak value,and the location of the leakage vortex moves front and back,and both of the phenomena indicate that the leakage flow is marked unsteady.