前飞状态下直升机旋翼旋转噪声预测

基于Farassat声学时域公式1A，建立了一个亚音速前飞状态下直升机旋翼旋转噪声的预测方法。该方法将厚度噪声与载荷噪声之和作为总噪声，将桨叶表面沿展向和弦向进行数值离散，延迟时间采用牛顿法求解，通过坐标转换，可针对不同位置观察点计算出声压的时间历程。并进一步利用傅立叶分解，进行噪声的频谱分析。应用该方法，分别进行声压与频谱的算例计算，并与可得到的试验数据进行了对比，验证了方法的有效性。在此基础上，着重分析了桨叶片数、旋翼转速、前飞速度等参数对旋翼气动噪声的影响，得出了一些有意义的结论。

Numerical prediction for the acoustic noise of helicopter rotor in forward flight

A numerical method based on the acoustic time-domain formulation 1A of Farassat is established to predict the acoustic noise of helicopter rotors in subsonic forward flight. In the present method, the total acoustic noise is calculated by the combination of thickness noise and loading noise. The blade surface is discretized along spanwise and chordwise directions and the retarded time is solved by the Newton＇s method so that the acoustic pressures of rotor noise at different observations can be numerically computed by the frame transformation and the spectral analysis of rotor noise signal can be performed by the Fourier transformation. Based upon the above method, the numerical examples on rotor noise pressure and spectral analysis are made, and the calculated results are compared with the available experimental data so as to validate the present method. In addition, the effects of the blade number, rotor speed and forward speed on the rotor noise are also calculated and analyzed. On the basis of calculations and analyses, a few meaningful conclusions are summarized.