复杂几何条件下伴随格林函数的数值求解

为简化气动噪声预测中复杂边界的网格处理,采用计算气动声学(CAA)方法与浸入式边界方法(IBM)相结合数值求解气动噪声预测所需的伴随格林函数.根据伴随格林函数的基本形式,文中设计了特定的圆柱声散射算例,并将数值结果与解析解对比,分析该方法的计算精度,验证了该方法在复杂几何边界条件下伴随格林函数求解中的适用性.最后应用该方法求解了考虑吊挂安装效应的锯齿型喷管喷流剪切层内的伴随格林函数.结果表明:由于喷流剪切层的散射效应,伴随格林函数在喷流内分布不均匀,最大值比最小值高出3倍以上,反映了喷流内不同区域声源对远场噪声贡献的差别,降噪设计可以重点考虑降低格林函数较大区域的声源强度以达到降低噪声的目的. 

Numerical solutions of adjoint Green's function for complex geometries

In order to simplify the grid generation during aerodynamic noise prediction, the computational aeroacoustic (CAA) method and immersed boundary method (IBM) were combined together to solve the adjoint Green''s function. According to the basic formulation of adjoint Green''s function, a special case of cylindrical acoustic scattering problem was designed. The comparison between the numerical results and the analytical solutions prove that the numerical methods used are reliable and feasible for the calculation of adjoint Green''s function for problems with complex geometries. Finally, the combined numerical methods were used to solve the adjoint Green''s function of the jet flow from a nozzle with chevron and pylon interaction. Result shows that, because of the scattering effect caused by jet flow shear layer, the distribution of adjoint Green''s function in jet flow is uneven, and the maximum value is 3 times higher than the minimum value. This simulation results reveal the relative importance of different regions with the same sound intensity to the far field noise. Therefore, low noise nozzle design can focus on reducing the sound intensity in the larger area of Green''s function.