Numerical Simulation Of Acoustic Radiation In Supersonic Mixing Layer

Acoustic radiation has long been a serious concern for Aircraft performance;consequently,it attracts more and more attentions from scientific researchers.In order to improve our understanding of the above problem,the study on the characteristics of acoustic radiation for supersonic mixing layer is carried out to further reveal its mechanism.In this paper,the computational domain is divided into two parts: near field and far field.The near field calculation is investigated by numerical simulation of PSE and NLDE.And an integral theory(Wu integral theory)based on stability theory is applied to predict the far field pressure of mixing layer.Main aspects of present study are summarized as follow:(1)The two mode unstable waves propagate along the fixed direction;Wu integral theory can reflect that Mach wave Emanates from the streamwise position at which the instability wave attains its maximum amplitude,and accurate reflect the physical characteristics of Mach wave propagating along two different directions of energy and phase.(2)The evolution of the unstable wave determines the concentration of the Mach wave energy.The shorter the range of amplitude change is,the smaller the influence range of Mach wave energy is;conversely,the larger the influence range of Mach wave energy is.(3)The temperature ratio is one of the important parameters affecting the acoustic radiation,and has different influence on the fast and slow mode.(4)The evolution of linear wave packets,nonlinear wave packets and far field acoustic radiation are studied by PSE,NLDE and Wu integral theory.The results show that the difference between the unstable wave frequencies affects the Mach wave radiation characteristics.For nonlinear wave packet,it is demonstrated that low-frequency waves resulting from nonlinear interaction are efficient in radiating sound,which is equivalent to producing a new sound source.