超音速射流啸叫模式切换不稳定性

详细信息

Instability of screech switch for underexpanded free jet

摘要: 超音速射流的噪声辐射有3个主要成分,即湍流的混合噪声、与激波结构有关的宽带噪卢以及离散的单频啸叫。其中啸叫离散基频特性具有多种模式,模式之间的切换是一个不稳定过渡过程,与流动纹影显示的不稳定相对应。模式切换过程中在频率特性上反映出一种模式的饱和、衰减,而另一种模式的强化,最终成为主导。这种切换过程中的频率变化很可能和流动失稳涡结构的破碎、配对相关联,利用线性不稳定性理论得到了与实验相符的不稳定波的增长率,分析了不稳定波最大增长率与啸叫频率切换的对应关系。

Abstract: For underexpanded supersonic jets three main components of noise radiation are turbulent mixing noise, broadband shock-associated and discrete tone screech. The screech frequencies show various multimodes. The process of mode switching is instability, while flow visualization using Schlieren photography show the unstable flow structure. The mode switching represents the sound pressure level at one mode frequencies decay and another mode stronger, being main mode. Accompanying discrete tone occurs until the end of mode switch. The characteristic of the screech frequencies are related to the instability of the flow and vortex. Linear instability wave theory indicates that the maximum growth rate of instability wave of the two azimuthal modes agrees well with measurement.