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目前基于雷诺平均Navier-Stokes(RANS)的喷流噪声预测方法在格林函数求解时,为简化求解过程,通常对喷流流动做平行流假设,对观测点做远场假设。随着格林函数求解方法发展,近年来的研究表明平行流假设对下游观测点格林函数的计算会引起较大偏差,而目前远场假设对格林函数求解的影响仍不清楚。为研究远场假设对喷流格林函数求解的影响,以二维喷流为例,采用计算气动声学方法(CAA)分别数值求解了观测点远场假设条件与实际条件下90°~150°方向喷流内伴随格林函数,进而分析远场假设对格林函数求解的影响。研究结果表明,对于不同方向的观测点,由观测远场假设导致的伴随格林函数求解偏差不尽相同,且对于越靠近喷流中心线方向的观测点,远场假设导致的偏差越大,其中150°方向观测点,采用远场假设后,格林函数计算结果最大偏差达到-15dB以上。因此,对于靠近喷流中心线方向的噪声观测点而言,为避免预测偏差,应采用实际观测条件求解喷流格林函数。
At present, when Rayleigh mean Navier-Stokes (RANS) jet noise prediction method is used to solve the Green’s function, the parallel flow assumption of jet flow is usually made and the far-field assumption of the observation point is made. With the development of the Green’s function method, recent researches show that the parallel flow hypothesis will cause large deviation to the Green’s function of the downstream observation point. However, the influence of far-field hypothesis on the Green’s function is still unclear. In order to study the influence of far-field hypothesis on the jet Green’s function, taking the two-dimensional jet as an example, the aerodynamic acoustics method (CAA) is used to numerically solve the far-field assumption of the observation point and the 90 ° ~ 150 ° direction under the actual conditions The jet flow accompanied by Green’s function, and then analyze the far-field assumptions on the Green’s function to solve the impact. The results show that for the observation points in different directions, the deviation of the Green’s function with the observed far-field assumption is not the same, and for the observation point closer to the jet centerline, the deviation caused by the far-field assumption is larger, 150 ° direction of the observation point, using the far-field assumption, the maximum deviation Green’s function results to -15dB or more. Therefore, for the noise observation point near the jet centerline, in order to avoid the prediction error, the actual observation conditions should be used to solve the jet Green’s function.