Kirchhoff方法在旋翼前飞噪声预测中的应用研究

将CFD(计算流体力学)技术与噪声预测的Kirchhoff方法相结合,发展了前飞状态下直升机旋翼远场气动噪声的定量预测方法,得到了旋翼噪声的时域解。先用具有解析解的“点源”流动代替旋翼流动,通过比较计算值与理论值,验证了该预测方法的可行性和可靠性;尔后针对AH—1／OLS旋翼模型的两种前飞状态进行计算,通过比较计算值与实验值,进一步验证了本文方法及其所发展的程序的正确性。

Aeroacoustic noise prediction of helicopter rotor in forward flight using Kirchhoff method

For modern helicopter rotor design, low noise radiation has been taken as one of the most important design targets. In the present work, upon use of CFD (Computational Fluid Dynamics) technologies and Kirchhoff formulation, an efficient method is developed as an analytical tool to reduce acoustic noise generated by rotor in forward flight. The flow field of rotor in forward flight is quite complex, especially when rotor blades work with unsteady loads. By use of "dual time stepping method" and moving grid-strategy, the 3D Euler's equations are numerically solved to obtain the near-field acoustic noise. Then, Kirchhoff formula is employed to calculate the acoustic pressure signal of far-field observing points base on the near-field solution. Kirchhoff formulation can be used to predict the noise radiation from moving surface, but the integration surface must be placed in the linear region of flow field because Kirchhoff formula is just the solution of linear wave equation. In this work, a nonrotating cylinder that covers the nonlinear flow region is generated as the integration surface and a high efficient 3D linear interpolation from CFD solutions is introduced. The integral is preformed on the integration surface, but the source variables are evaluated at the retarded time. To examine the correctness of the implementation of our method, the pressure signal of a simple point source flow and an AH-1/OLS model rotor in forward flight are calculated. The computed result shows good agreement with the theoretical solution and experimental data, respectively, and it indicates that our method is efficient and is capable of capturing the nonlinear quadrupole noise for transonic rotor.