非线性扰动方程研究平面混合层发声机制

在流动过程中由脉动引起的噪声问题在自然界和工业界中广泛存在，研究流动过程中不稳定波的发声机制对于理解、预测并最终控制气动噪声有着重要意义。本文以二维 Blasius 相似性解作为基本流场，以超声速混合层作为研究对象，采用非线性扰动方程(NLDE)研究超声速混合层不稳定波的近场动力学特性与远场声辐射之间的内在联系。针对不同类型的对流马赫数，分别研究对流马赫数 Mc =0.5(<1)和 Mc =1.2(≥1)两种情况下的扰动发声机制，结果表明：当对流马赫数 Mc <1时，流场中的发声机制主要由大尺度结构的涡条发声，且基本波与亚谐波之间的非线性作用能增强辐射强度；当对流马赫数 Mc ≥1时，根据扰动相速度是相对于上层还是下层自由流速度为超声速，可以进一步分为快慢两种模态，分别对快慢两种模态以及其相互作用模态进行了数值模拟研究，计算得到流场中的发声机制是以马赫波形式辐射向远场，即马赫波辐射，其辐角的计算结果与理论值相符。

Studing sound generation mechanisms of mixing layer using nonlinear disturbance equations

The noise problem caused by pulse exists in the aviation and natural industry, studying sound generation mechanism of the unstable wave is of important significance for under-standing,predicting and controlling the aerodynamic noise.In this paper,Nonlinear Disturbance Equation (NLDE)is used to study the relationship between near field dynamic characteristic and the far field sound radiation for supersonic mixing layer.For different types of convective Mach number,disturbance pressure are selected and calculated respectively.It is gained two different sound generation mechanisms.When the convective Mach number of supersonic mixing layer is less than 1,the sound is generated by the large-scale vortex structure in near-field.Otherwise, the generation of sound is depended on whether the phase velocity of disturbance is supersonic relative to the upper flow or not.It turned out that the supersonic part of the disturbance pressure radiate to far-field at a fix angle,that is so called Mach wave radiation.The calculated angle of Mach wave is consistent with the theoretical one.