非紧致阻抗圆柱气动噪声数值预测与控制方法

Numerical Prediction and Control Method of Aerodynamic Noise from a Non-compact Circular Cylinder with Impedance Boundaries

为预测非定常流动与非紧致阻抗固体边界相互作用产生的气动噪声,开发一种基于精确格林函数和声模拟理论的气动噪声数值预测方法。非紧致阻抗边界对声波的散射作用计入精确格林函数,远场噪声采用FW-H方程计算。对具有任意几何外形的非紧致阻抗边界,采用边界元方法计算满足声学硬边界或声学阻抗边界条件的精确格林函数。同时,推导了具有阻抗边界条件的二维非紧致圆柱精确格林函数的解析解用以验证数值计算方法。数值计算结果表明数值解与解析解的结果一致,数值解要取得好的网格收敛效果需要在一个波长内布置至少20个网格点。圆柱绕流气动噪声预测结果表明,非紧致边界的阻抗特性对声传播有显著影响,采用合适的阻抗布置方式可以取得有效的噪声控制效果。

In order to predict the noise induced by the interaction between the unsteady flow and the solid boundaries,an aerodynamic noise prediction method is proposed based on the exact Green’s function and acoustic simulation theory.The scattering effect from the non-compact bodies with impedance boundaries is evaluated by the exact Green’s function.The sound far-fields are predicted with the FW-H equation. For the boundaries of arbitrarily shaped non-compact bodies, theBEM is used to calculate the exact Green’s function which satisfies the acoustic hard boundary condition or impedance boundary condition. Meanwhile, the analytical solution of the exact Green’s function for a two-dimensional non-compact cylinder with an impedance boundary condition is derived for validation. The results show that the numerical solution and the analytical solution are in excellent agreement when the number of the grid points per acoustic wavelength reaches 20.Moreover, the impedance of the non- compact body has a strong impact on the sound propagation. An effective noise reduction can be achieved if the impedance is properly distributed.