轴向非均匀凹槽叶顶的实验与数值研究

为探究不同轴向非均匀凹槽间隙控制泄漏流动的效果和机理,采用实验与数值结合的研究方法,对两种间隙条件下的叶顶凹槽结合渐缩型间隙、均匀型间隙和渐扩型间隙方案对涡轮叶顶泄漏流动的控制效果进行研究。结果表明:减小泄漏流流量与控制叶栅总压损失之间没有直接联系,渐扩型间隙增大了26.7%的泄漏流流量,但在小间隙和大间隙条件下分别减小了2.44%和3.53%的总压损失；渐扩间隙减小总压损失,是通过有效减小通道涡在节距向和展向的尺度,并在一定程度上减小泄漏涡在节距向的尺度实现的；渐扩间隙减小通道涡和泄漏涡的尺度,其原理在于渐扩间隙的布置增强了凹槽内的径向流动,使压力面再附线更靠近叶片,吸力面泄漏涡分离线位置更靠后,从而抑制了泄漏流动。 

Experimental and numerical study on axially non-uniform clearances with a squealer cavity tip

Experimental method and numerical method were both used to study the effect and mechanism of the axially non-uniform clearances on turbine leakage flows with a squealer cavity tip. Two clearance heights and three clearance types: shrinking clearance, uniform clearance and expanding clearance, were investigated. The following findings were made. Firstly, there was no relation between the reduction of the leakage mass flowrate and the reduction of the total pressure loss. The leakage mass flow rate increased by 26.7% under the expanding clearance case, while the corresponding total pressure loss achieved a 2.44% reduction under small clearance and a 3.53% reduction under large clearance. Moreover, the reduction of the total pressure loss was obtained by the decrease of the scale of the passage vortex in pitch-wise and in span-wise directions and the decrease of the leakage vortex in pitch- wise direction. The arrangement of the expanding clearance strengthened the span-wise flows of the leakage flows in the squealer cavity, led to a closer reattachment line with the blade on the pressure side and a further back leakage vortex separation line, and finally restricted the leakage flows.