叶片前缘形状对涡轮气动性能的影响

采用Bezier曲线控制涡轮叶片前缘形状由圆弧形改为非圆弧形,用数值计算方法研究涡轮叶片前缘形状对其气动性能影响.首先以基元叶型为研究基础,数值模拟分析、比较不同基元叶型前缘形状在不同攻角下对涡轮叶栅性能影响.对于正常运行的攻角范围(-15°～+10°),由于非圆弧形前缘表面曲率半径增大较缓,减小了前缘表面流动的法向压力梯度,抑制过度膨胀,减小由摩擦力引起的能量耗散,损失减小,且非圆弧形曲率半径越大,提高性能效果相对越好.而在非设计工况的大攻角条件下,前缘曲率半径缓慢增大将导致叶型分离更严重,损失相对增加.其次以某5级低压涡轮作为验证实例,数值研究分析认为,非圆弧形前缘形状可改善叶片前缘流动特性,提高涡轮效率,但对于远离设计点的非设计工况,由于气流攻角的大幅度改变,会带来涡轮气动性能的负面影响.

Effect of blade leading edge on aerodynamic performance of turbine

Geometry of turbine blade leading edge was altered from circular to non-circular by using the Bezier curves methods,based on which numerical analysis and comparison were made to illustrate how turbine cascade leading edges affected the aerodynamic performance under different attack angles.Within the normal operating range of attack angle (-15°~ +10°),the non-circular leading edge had a better performance as the gradual increase of the curvature radius of the non-circular leading edge reduced the normal pressure gradient of the leading edge,which further restrained the flow from excessively expanding and reduced the energy dissipation caused by the viscous stress,resulting in a decreased flow loss,and the bigger the curvature radius of the non-circular leading edge,the better the performance.Whereas under the large attack angle of the non-design condition,the gradual increase of the curvature radius would cause more severe cascade separation,which aggravated the loss,and it was exemplified by the case of a five-stage low pressure turbine.Numerical analysis has indicated that the non-circular leading edge can improve the flow features and increase the turbine efficiency.However,for the non-design condition estranging from the design point,the flow attack angle alters so substantially that it has negative effect on the turbine aerodynamic performance.