Numerical Study On Aerodynamic Performance Of Highly Loaded Compressors With Endwall Boundary Layer Suction

The development of advanced aero-engine technology has always placed increasing demands on thrust-weight ratio and aerodynamic efficiency.The high load diffuser profile was designed to meet the requirements of high stage pressure ratio,however it brings about the problem of deterioration of secondary flow and increased separation of flow inside the cascade channel.In order to solve this problem,the boundary layer suction technology is adopted in the high-load diffuser cascade to improve the degree of the flow separation and secondary flow deterioration in the cascade channel,optimize the flow field structure,and improve the aerodynamic performance of the cascade,and which has been proved by a lot of research to be a promising and practical way of flow control.In the paper,numerical simulation study was carried out in rectangular vane cascade,which is composed of high load diffusing vane type of NACA0065-K48.The study was carried out using the commercial CFD software ANSYS CFX,and the SST(Shear Stress Transport)turbulence model was selected.The numerical method was effectively checked.The total pressure loss coefficient was used as an index to measure the aerodynamic performance of the cascade.Wall limit flow pattern,profile static pressure coefficient distribution and vortex identification criteria(vortex criterion / Q criterion)were selected as flow analysis methods in the paper.Firstly,variable attack angle characteristics of flow field structure and aerodynamic performance of original cascades were studied.Then a stream wise slot was set up near the blade root in the middle of the cascade passage for end wall boundary layer suction.The control mechanism of the flow field structure optimization and aerodynamic performance improvement for the high-load diffuser cascade in the wide variation angle range was obtained through systematic research and comprehensive analysis.The research in this paper shows that,in addition to the typical vortex categories found in previous studies,there are two concentrated shedding vortices located at the area of the corner/the trailing edge of suction surface and the corner/the trailing edge of pressure surface in the flow field of high load diffusing prototype cascade channel,and these two vortex structures have a significant influence on the aerodynamic performance of the cascade.The prototype cascade is with the smallest loss at the design attack angle(i=-6°),and the cascade aerodynamic performance is deteriorated sharply as the attack angle increases within the positive attack angle range.The cascade is stalled at the attack angle i=6°.The losses caused by the corner separation and the boundary layer separation on suction surface occupy the main parts of the cascade flow losses.Research about end wall boundary layer suction finds that the total pressure loss of high load diffuser cascade can be effectively reduced with an appropriate aspiration flow rate in a wide range of variable attack angle(i=-9°~6°).In the research,the optimal aspiration flow rate increases from 0.5% to 2.0% of the inlet flow rate with the attack angle increase.When the attack angle is not greater than zero degree,with the aspiration flow rate increased to a certain extent,the corner separation pattern is changed from closed separation to open separation,combined with the separation starting point moving to the position of the blade root at the rear end of the suction slot,and the corner separation is delayed and effectively weakened with the separation range reduced greatly.The end wall boundary layer suction cause that the concentrated shedding vortex at the corner/ the trailing edge of suction surface is eliminated,and the passage vortex is weakened,so that the aerodynamic performance of the cascade is greatly improved.Continuing to increase the aspiration flow rate on this basis,the gain growth is not obvious.While the aspiration flow rate is 2.0% of the inlet flow rate in the suction cascade with attack angle i=0°,the total pressure loss coefficient is reduced by 41.4% compared with the original cascade.When the attack angle is greater than zero degree,because the suction slot is located in separation area distant from the downstream of the corner separation start point,only with a large aspiration flow rate can the low-energy fluid in the separation zone of the corner zone be absorbed and the mixing reduced,along with the separation degree of boundary layer on suction surface reduced to a certain extent,but suction cannot essentially change the separation pattern of the corner regions of the cascade channel.It finds that if the aspiration flow rate is small,the aerodynamic performance and flow field structure of the cascade will even be deteriorated.