管道后传声数值模拟的不稳定波抑制

Suppression of Instability Waves in Numerical Simulations of Sound Propagation From Aft Ducts

在管道后传声的数值模拟中,必须考虑平均流剪切层的散射效应,然而在非均匀剪切流动下时域求解线化欧拉方程会面临Kelvin-Helmholtz不稳定波产生和放大的难题。已有的不稳定波抑制技术通常很难获得令人满意的结果。本文采用一种混合方法,首先引入有限时段的宽频声源波包将声波和不稳定波分离,进而采用声源滤波器技术对不稳定波进行抑制。数值验证算例选择半无限长轴对称环形硬壁直管道,采用计算气动声学方法时域求解2.5维线化欧拉方程,无背景流动的数值解与解析解符合很好,验证了程序的精度与可靠性,非均匀流动算例则表明所采用波包加声源滤波器混合方法对不稳定波抑制效果明显,对声场影响很小,充分显示了该方法的精度与可行性。

The scattering effects from mean flow shear layer should be accounted for in the numerical simulation of sound propagation from aft ducts.However,the time domain simulation of the linearized Euler equation has to face the difficulties of the generation and amplification of Kelvin-Helmholtz instability waves in non-uniform shear flows.The available methods for the suppression of the instability waves are difficult to give satisfactory results.The main objective of this paper is to check the feasibility of a hybrid method.Firstly,a broadband sound source wave packet with limited time span is introduced for the separation of acoustic waves from instability waves.Then,a source filtering technique is adopted to suppress the instability waves.Half infinitely length annular ducts are selected for numerical validations.The 2.5D linearized Euler equations are solved in the time domain with a computational aeroacoustics approach.Numerical results agree fairly well with analytical solutions for no mean flow cases which show the accuracy and reliability.Furthermore,it is demonstrated that the wave packet method with the help of source filtering technique can remarkably suppress the instability waves without the influence to the sound field for non-uniform mean flow cases.