低速湍流中气动噪声预测方法

 为了研究气动噪声的产生机理和传播过程,在考虑介质黏性的影响情况下,采用分解法并结合湍流模型,对低速湍流流动中气动噪声问题在时域上进行数值计算。基于非结构化同位网格和有限体积法,把可压缩N-S方程分解成不可压N-S方程、含黏性项的声扰动方程;为了考虑质点振速和声压耦合,采用SimpleC算法来同步求解不可压N-S方程和声扰动方程。进出口远场边界采用以渐近解为基础的无反射边界条件,并采用与内部区域相对应的有限体积法、时间隐式格式对其进行求解。利用所编制的程序进行层流状态下圆柱绕流气动噪声仿真验证,并与文献结果进行对比,检验本方法的正确性;并结合湍流模型将数值解法推广到湍流状态下气动噪声数值模拟中。结果表明该方法能够很好地反映流场和声场的形态,无反射边界能很好地抑制声波在边界处的反射,适合低速流气动噪声问题模拟,为实际工程中的降噪工作提供预测信息。

A Prediction Method for Low-speed Turbulent Flow Noise

In order to study acoustic noise generation and propagation while considering that internal viscosity of the propagation medium affects the results of aeroacoustics numerical simulation, a decomposition technique and a turbulent model were introduced in time-domain. Based on an unstructured collocated grid and finite volume method, the compressible N-S equation was divided into a viscous incompressible N-S equation and the viscous perturbation equation, and a SimpleC algorithm was used to solve the problem of velocity-pressure decoupling. Appropriate non-reflecting boundary conditions were adopted at the inflow and outflow boundaries. The governing acoustic equations of boundaries are discretized over finite volume method and the transient term is discretized by the second-order Euler implicit scheme. Numerical simulation of noise induced by flow around a circular cylinder at small and big Reynolds number has been conducted and compared with the aeroacoustic theory in time domain, in order to study the effect of viscosity on aeroacoustic numerical simulation. Comparing the two results, good results and more details about flow and sound could be obtained by splitting method, which could be used to provide some information for reducing the noise in actual engineering. The work demonstrated that the numerical algorithm can be used for the simulation and analysis of flow-induced noise at a flow with low speed.