Research On Internal Flow Mechanism And Control Strategies Of Boosters At Low Reynolds Numbers

For the high-altitude cruising power plant,the pressure and density of the inlet airflow are significantly lower than the ground conditions,which makes the Reynolds number of the chord representing the Reynolds number of the compression system at a low level,and the low-energy fluid in the boundary layer on the blade surface is easier to separate under the combined action of the thicker boundary layer and the reverse pressure gradient,which leads to the serious degradation of the performance and stability margin of the booster,further affecting the performance of the compression system and the engine.In order to solve this problem,this paper studies the boundary layer flow mechanism and suction control method of high subsonic compressor airfoil and 1.5 stage booster under low Reynolds number by CFD numerical method,which provides theoretical support for the flow control of booster under low Reynolds number.Firstly,for a typical high subsonic airfoil with similar flow characteristics to the booster airfoil,the flow characteristics of the blade boundary layer are analyzed at different Reynolds numbers and angles of attack,and the influence mechanism of boundary layer suction regulation on the airfoil flow and performance is studied.With the decrease of Reynolds number,the blade suction surface separation bubble length increases,the boundary layer thickens,the flow blockage in the blade passage and wake mixing intensifies,the blade loss increases and the aerodynamic performance deteriorates.Using boundary layer suction in front of the separation point of blade suction surface can effectively delay flow separation,shorten the length of separation bubble,and reduce blade loss;There is an optimal suction flow rate for different sizes of suction slots,so that the total pressure loss is relatively low.Under low Reynolds number conditions,the total pressure loss of the blade decreases by 33.9%and 70.1%respectively at 4° and 9° after suction control.At negative Angle of attack,blade loss increases after suction control due to the changes of blade suction surface load characteristic distribution.Secondly,the characteristics of boundary layer flow under low Reynolds number conditions were analyzed for the 1.5 stage booster of a typical high-altitude long-endurance engine,and the regulation effect and mechanism of boundary layer suction on the stator flow of the booster were discussed.From the ground to the altitude of 20km,the Reynolds number decreases by one order of magnitude,the peak efficiency of the booster decreases by about 3.76%,and the pressure ratio near the stall point decreases by about 3.6%.The aerodynamic performance and stability margin of the booster can be improved by the control of boundary layer suction on the suction surface of the stator blade.The suction flow rate will affect the efficiency and margin of the booster.At the maximum efficiency of the booster,the flow in the near wall area of the stator suction surface are improved and the loss is reduced after suction control.However,in some working conditions and blade height,the suction control has not achieved a good improvement effect due to the suction slot location and low suction flow rate.On the contrary,the flow in the blade passage are deteriorated due to the pit disturbance of the suction slot on the suction surface of the stator blade.Under conditions near the stall point,the flow in the blade passage deteriorated significantly,the suction control improves the flow at the blade root and reduces the loss;However,at the tip of the blade,the small suction flow rate could not improve the flow in the near wall area,and the flow in the blade passage were further deteriorated,and the total pressure loss increased significantly.The suction control could not significantly improve the aerodynamic performance and flow of the stator blade at the near stall point.