周期性压力波动对气膜孔流动特性影响的研究

针对主流周期性压力波动的非稳态气膜冷却现象,分别采用非稳态及准稳态数值模拟进行了计算,通过对比揭示了非稳态气膜冷却现象的特征。结果表明:相对于主流的压力波动,气膜孔出口受到上一个时刻压力的影响,呈现出了波动延迟特性;针对本文所研究的波形特点,压力波动一方面导致压差(二次流与主流压力差值)变化无法快速直接地影响到二次流流动,阻止了倒流的发生,使得二次流流量更加稳定;另一方面,其携带的压力波动效应使得气膜孔出口形成贴壁性较好的环向外旋涡,将喷射出去的二次流重新带回壁面,使得二次流贴敷壁面。对于某一特定的主流波动特性而言,是存在在最佳设计长径比使得气膜孔质量流量特性及防止倒流特性达到最佳。本文研究对于涡轮周期性压力波动作用下的气膜孔气膜冷却研究具有较大的意义。

Study on the Unsteady Film Cooling Characteristics With Periodic Pressure Fluctuations

Unsteady and quasi-steady steady numerical simulation were carried out to investigate the film cooling characteristics of the unsteady film cooling performance,for mainstream with periodic pressure fluctuations.The results shows that:compared with the pressure fluctuations in mainstream area,gas film hole outlet influenced by the pressure at previous point in time,which results in the pressure fluctuation delay characteristics;For the waveform studied in this paper,the pressure fluctuation delay leads to pressure difference(between secondary flow and the mainstream) can not affect the secondary flow quickly and directly on the one hand,which prevents backflow and won more stable mass flow rate of secondary flow;On the other hand,the pressure fluctuation carries such outward rotation of the vortex in the circumferential direction which close to the casing surface outlet of the film cooling holes.The vortices bring secondary flow which has ejected back to the wall,so that the secondary flow is close to the casing surface.For mainstream characteristic of a particular periodic pressure fluctuations condition,it is present in the best design so that mass flow stability of the film cooling hole and preventing backflow characteristics are also the best.This paper bring the study of film cooling turbine film cooling holes under periodic pressure fluctuations a greater significance.