非轴对称端壁抑制叶栅二次流分离的实验研究

Experimental Research on Contoured Endwall Depressing Cascade Secondary Flow Seperation

应用热线测量和颗粒图像测速(PIV)技术,测量平端壁叶栅(FEW)和非轴对称端壁叶栅(CEW)的二次流动。基于叶栅内的涡结构和剪切应力,分析非轴对称端壁降低二次流损失的流动机理。实验结果表明:二次流在叶片吸力面的边界层分离导致壁面涡与主流流体的剪切掺混,这是叶栅二次流损失的主要来源;非轴对称端壁通过降低端壁横向压力梯度推迟二次流分离的发生,使壁面涡与主流区产生剪切掺混的范围缩小,并使端壁二次流的流向速度提高、壁面涡的强度降低,在上述两方面作用下叶栅内的剪切应力减小,叶栅二次流损失降低。

The secondary flow in the turbine cascades with flat endwall(FEW)and contoured endwall(CEW)is measured by use of hot wire anemometer and particle image velocimetry(PIV)technologies.The vortical structure and shear stress of the cascades are used to analyze the flow mechanism of the secondary flow loss reduced by CEW.The experimental results show that the separation of secondary flow on the boundary layer of the blade suction surface,resulted in the shear mixing between main flow and wall vortex,which is the main source of secondary flow loss of the cascade.Application of contoured endwall reduces the crosswise pressure gradient of the endwall to delay the separation of the secondary flow,which reduces the shear mixing space between the endwall vortex and the main flow,accelerates the streamwise speed of secondary flow of endwall and reduces the strength of wall vortex,contributing to the reductions of the shear stress and secondary flow loss of the cascades under the effect of the above two aspects.