Numerical And Experimental Study Of Corner Separation In A Compressor Stator Cascade Based On CDA Blade Profile

The paper has studied the performance of the cascade based on CD A blade profile and corner separation mechanism as well as the influence factors via the experiment and numerical method. In the experiment, the loss, turning angle, pressure on the blade and oil-flow visualization of suction surface and endwalls are measured at the relative wide range of inlet attack of angles(AOAs), which is contribute to the better understanding of corner separation and calibrating the CFD tools. In the numerical study, the realistic distribution of inlet velocity and turbulence intensity are used in the computation, adding transition model and taking consideration of the decay of inlet turbulence intensity and the influence of yplus of wall grids. The more comparisons between experimental and numerical results are investigated to test the accuracy and reliability of the CFD method. Finally, the paper has studied the effect of AOA, turbulence intensity, Mach number/Reynolds number, thickness of inlet boundary layer and the fiilets at end of blade on the compressor corner separation. It turned out that:According to the loss characteristics of cascade, the paper divided the whole AOA ranges into three parts:large negative AOAs, the design AOAs and the corner stall AOAs. Near the large negative AOAs, although the suction side of cascade and endwalls don’t appear the evident corner separation, the large separation flow is happened near the leading edge of pressure side, and the laminar separation bubbles appear near the trailing edge of suction side. When the AOA increasing, the loss of cascade will decline. Near the design AOAs, the loss of cascade is relative low and almost constant when the AOA changes. The separation flow of pressure side is disappeared and the laminar separation bubbles is moving to mid of chord. The slight corner separation is happened on the suction side and its size will grow up lineally with the increasing of AOA. When the AOA is greater than-3.6deg, the loss of cascade will go up suddenly, the corner stall will happened, which means the corner separation are found both on the suction side and endwalls. During the corner stall AOAs, the corner stall structure and loss of cascade are both rising with the increasing of AOA.The paper studied the effect of inlet turbulence intensity on cascade loss and flow structure at design point. It is found that the changes of inlet turbulent intensity mainly have an effect on the laminar separation bubbles on the suction side of cascade. The scale of corner separation on suction side will reduce when the laminar separation bubbles on the blade is removed due to the turbulence intensity increasing. If the intensity of inlet turbulence keeps on increasing, the flow structure is almost constant. The loss at mid-span will decrease first and then increase.The paper take four kinds of Mach numbers(Ma)/Reynold numbers(Re) to conduct numerical study. It is turned out that corner separation on the suction side always exist in spite of the laminar separation bubbles will disappear when the Ma/Re increasing. When the Ma increases to 0.5, corner separation grows to corner stall.The inlet boundary layer velocity distribution experimentally has good agreement with seventh-power law of turbulent theory. The paper take the law to obtain three different thickness inlet boundary layers and go on numerical study at design point. It concluded that: the thicker inlet boundary layer, the bigger corner separation scale.Finally, the paper uses the numerical simulation to study the effect of blade fillets on the corner separation at design AOAand corner stall AOA. It is found that corner separation and corner stall will be reduced clearly if the radius of fillet will be increased properly. The cascade experiment with fillets are investigated to verify the numerical results. It turned out that the tendency of experiment have good agreement with numerical study. This is because that circumferential pressure gradient increasing due to cascade become thicker when adding fillet is benefit to balance the centrifugal force of flow. When the radius of fillet increases, this phenomenon will be more obvious. At the design AOA, the loss distribution of spanwise changes little though adding fillets make the corner separation reduce to some extent. However, at corner stall AOA, the loss at mid-span remain constant but the loss near the endwall reduce when increasing the size of fillets.