尾缘锯齿结构对低压涡轮动静干涉噪声的影响

Effects of Trailing Edge Serrations on Rotor/Stator Interaction Noise in Low-Pressure Turbines

关键词:  轴向间距  尾缘锯齿  低压涡轮  干涉  气动噪声

Key words:  Axial gap  Trailing edge serration  Low-pressure turbine  Interference  Aerodynamic noise

摘要:

为满足现代航空发动机“更紧凑的级间距、更高的经济性和更低的噪声”的设计目标，低压涡轮轴向间距设计得越来越小。然而，较小的轴向间距将严重影响涡轮的气动性能及动静干涉噪声，这对流动及噪声控制方法提出了更高的要求与挑战。为此，采用大涡模拟结合FW-H方程研究了不同轴向间距情况下，上游静叶尾缘采用短、长锯齿结构时，一级低压涡轮叶栅动静干涉噪声及气动性能的变化规律。结果表明：轴向间距的缩短会导致低压涡轮气动性能恶化，下游动叶前缘受到更强的逆压梯度和“逆射流”效应，从而增大动静干涉噪声；上游静叶采用锯齿尾缘结构，产生于锯齿根部的微射流可以抑制“逆射流”效应，消除分离泡，削弱非定常干涉效应，提升气动性能，降低动静干涉噪声；较短轴向间距情况下，长锯齿尾缘静叶降噪效果更好，相较于原型静叶，长锯齿尾缘静叶可降低尾迹亏损47.71%，流量提升8.65%，总压恢复系数提升0.88%，在1BPF（Blade passing frequency）和2BPF处单音噪声分别降低8.7dB和11.8dB，降低A记权声压级9dB。在缩短轴向间距情况下，静叶尾缘采用仿生锯齿结构，能同时实现气动性能的提高和噪声的降低。

Abstract:

In order to achieve the design goal of ‘more compact axial gap， higher economy and lower noise’ of modern aeroengine， the axial gap of low-pressure turbines is designed to be shorter. However， the shorter axial gap will seriously affect the aerodynamic performance and rotor/stator interaction noise of the turbines， and higher requirements and challenges are put forward for flow and noise control methods. Therefore， the large eddy simulation and FW-H equation were used to study the rotor/stator interaction noise and aerodynamic performance changes of a one-stage low-pressure turbine cascade when the trailing edge of upstream stator adopts short or long sawtooth structures under different axial gaps. The results show that the shortening of the axial gap will cause the deterioration of the aerodynamic performance of the low-pressure turbine， and the leading edge of the downstream rotor will experience a stronger adverse pressure gradient and ‘negative jet’ effect， thereby increasing the rotor/stator interaction noise. The micro-jet generated by the serrated structure of the trailing edge of the stator can suppress the ‘negative jet’ effect， eliminate separation bubbles， weaken the unsteady interference effect， improve aerodynamic performance， and reduce noise. In the case of short axial gap， the noise of long serrated trailing edge is lower. Compared with the base model， the long serrated trailing edge stator can reduce the wake loss by 47.71%， increase the mass flow by 8.65%， increase the total pressure recovery coefficient by 0.88 %， reduce the tonal noise of the 1BPF （Blade passing frequency） and 2BPF by 8.7dB and 11.8dB， respectively， and reduce the A-weighting sound pressure level by 9dB. In the case of shortening the axial gap， the trailing edge of the stator adopts a bionic sawtooth structure， which can achieve both aerodynamic performance improvement and noise reduction.