涡轮叶栅二次流的热线实验研究

采用旋转单丝斜热线测量涡轮平面叶栅出口周期性三维流场,借助于Matlab的Lsqnonlin最优化函数对热线测量数据进行最小二乘拟合以求解三维速度平均量。搭建了亚音速叶栅试验风洞,研究在2种不同进口流量和3种不同的叶片高度下,热线测得的叶栅出口瞬态速度场,并分析叶栅出口的二次涡流动情况。通过比较不同的叶栅工况,发现高速进口较低速进口叶栅尾迹明显,二次流强度较大;而较小的叶高下二次流较为剧烈,导致叶栅出口平面内径向流动速度(u)、垂直于出口平面的轴向速度(w)的迅速增大和出口平面内周向流动速度(v)的显著降低。叶高的减小和气动负荷(速度)的增加都会极大地提高叶栅的二次流损失,本质上都归咎于叶栅横向压力梯度的增大。

Hotwire-based Experimental Study of Secondary Flows in Turbine Cascades

The periodical three-dimensional flow field at the outlet of a turbine plane cascade was measured by using rotary single-wire slanting hotwires and a mathematical solution to the three-dimensional speed average value was accomplished by using a least square fit of the hot-wire measured data with the help of the LSQNONLIN most optimized function of Matlab.A sub-sonic cascade test wind tunnel was set up to study the transient speed fields measured by hotwires at three different blade heights and two different inlet flow rates and analyze the secondary vortex flow conditions at the cascade outlet.By comparing different operating conditions of the cascade,it has been found that the cascade with a high inlet flow speed has a more conspicuous wake zone and more intensive secondary flows than those with a low inlet flow speed.The cascade with a relatively small blade height,however,has more drastic secondary flows,resulting in a quick increase of both radial flow speed (u) in the outlet plane of the cascade and axial flow speed (w) perpendicular to the outlet plane and a dramatic decrease of circumferential flow speed (v) in the outlet plane.Both the decrease of blade height and the increase of aerodynamic load (speed) will greatly increase the secondary flow losses of the cascade,which can be substantially ascribed to an enhancement of transversal pressure gradient of the cascade.