旋翼前飞气动噪声高效数值算法研究

On Improving HSI Noise Prediction for Helicopter Rotor in Forward Flight When Flowfield is Partially near Sonic Speed

采用“双时间法”数值求解旋翼前飞非定常欧拉方程 ,并在此基础上 ,运用改进的 Kirchhoff方法 ,将近场流动解作为声源信号 ,积分求得旋翼前飞时产生的远场气动噪声 (高速脉冲噪声 ) ,从而发展了一套“流场→声场”的高效算法。为了保证网格生成效率 ,采用无限插值理论生成绕旋翼O-H型代数网格 ,并考虑了桨叶作变距运动的网格生成问题。解决了前飞噪声计算所遇到的计算机存储量过大、CPU时间过长的问题 ,并给出了定量计算结果 ,可作为研究旋翼声场机理及直升机降噪设计的基础。

Brentner′s Method, in our opinion, will run into complications in the case of predicting HSI (high speed impulsive) noise for helicopter rotor in forward flight when Mach number of advancing blade is close to 1. So we propose developing another method to deal with this special situation more satisfactorily. Section 2 discusses in detail how we simplify the algorithm of our method. Subsection 2.1 simplifies Kirchhoff formula by choosing a non rotational surface; this simplification prevents the Doppler singularity of Kirchhoff formula from complicating our calculations. Subsection 2.2 discusses the efficient interpolation from CFD (computational fluid dynamics) solutions. Section 3 gives the HSI noise results for UH 1H rotor model computed with our algorithm. Figs.4 and 5 in section 3 give the HSI noise results for forward flight when the flowfield of advancing blade is near sonic speed. The results in Figs.4 and 5 show preliminarily that our algorithm does improve the HSI noise prediction for helicopter rotor in forward flight when the flowfield of advancing blade is near sonic speed.