Mechanism Investigation On The Effect Of Wake Shape On Flow Of High-load Low-pressure Turbine

Turbofan engine with high bypass ratio is widely used in civil aircraft.Low pressure turbine as one of the important components,its working efficiency directly affects the performance of the engine.Therefore,high load blades are generally used to improve the economic benefits of the engine.However,under the condition of high altitude and low Reynolds number,the boundary layer of low pressure turbine blade is easily separated,which increases the loss of blade shape and leads to a sharp decline in aerodynamic performance of low pressure turbine.The periodic wake of the upstream blade will induce the boundary layer transition in advance,so as to suppress the boundary layer separation.This paper adopts the method of combining experiment with numerical simulation to study the important mechanism of the effect of wake on the boundary layer flow of low pressure turbine.This article addresses the following issues:Before the formal experiment,due to the measurement error of the hot-wire near the wall,the experimental platform was set up and finally it was found that the material near the wall and the incoming wind speed affected the final measurement results,which paved the way for the subsequent formal experiment.Hot wire and hot film technology were used to capture the flow information in a planar cascade experiment.A variety of characteristic parameters are processed to explore the development of boundary layer flow on suction surface under different working conditions.The influence mechanism of wake on the transition time and scale of suction surface under different working conditions is discussed.On the other hand,CFX commercial software was used to conduct a detailed study on the development of wake in the cascade channel under experimental conditions,and the influence of the development of wake under different conditions on the boundary layer separation on the suction surface was discussed.The results show that the boundary layer of suction surface will separate under steady state,and the unsteady wake of upstream blade obviously inhibits the separation of boundary layer of suction surface.As an important mechanism of wake effecting the transition and separation of boundary layer,Reynolds number and reduced frequency have a profound impact on the flow development of boundary layer.With the increase of Reynolds number,the starting position of the transition moves to the upstream of the blade.The turbulent boundary layer formed after the transition has strong anti-separation ability,and the separation area of the boundary layer is reduced.At low reduced frequency,there is still a long separation period in the boundary layer of the suction surface.Under the condition of high reduced frequency,the separation time is obviously shorter because the wake frequently acts on the boundary layer of suction surface,which will reduce the flow loss caused by boundary layer separation.