噪声在均匀流等截面圆环形排气管道中声传播的数值模拟

 应用模态分析方法对转/静干涉噪声在敷设声衬的风扇静子后排气管道中的声传播,声衰减进行了数值模拟。前传声波在遇到声导纳间断面时,声波反射模态增加,前传模态相应减少,因此可利用多段声衬声导纳间断面上的模态反射来抑制管内噪声的传播。计算并分析了均匀流情况下声衬声阻和声抗对管内消声量的影响。在高频声源和大Mach数气流情况下,随声阻或声抗变化,噪声衰减量都存在局部峰值和波动,此时不再呈现低频情况下的单调特征。因此,选择适当的声衬阻抗可有效地抑制发动机噪声传播。

NUMERICAL SIMULATION OF SOUND PROPAGATION IN AN ANNULAR EXHAUST DUCT IN THE PRESENCE OF UNIFORM FLOW

Numerical simulation of propagation of rotor / stator interaction noise in turbofan exhaust duct which is assumed to be made up of annular ducts with axially segmented treatments is developed by the mode analysis method. By quantitatively predicting the change of the mode coefficient distribution of forward and backward propagating acoustic energy at the segment interfaces, the attenuation of interaction noise is also investigated. The results manifest that when the forward travelling sound waves pass through the admittance discontinuity planes, the modal reflection will increase and the forward modes of waves will decrease. So the modal reflection at the interfaces can be utilized to suppress propagation of the in-duct noise. In addition, the effects of the change of resistance and reactance of liners on the suppression are theoretically calculated. It can be concluded that in the presence of high frequency source and high Mach number flow, whether for the change of resistance or for the change of reactance, there exist local peak values and fluctuation of the in-duct suppression, and at this moment, the monotonicity of suppression with the change of resistance and of reactance will no longer come into existence. Therefore, it is necessary for the engine noise reduction to choose adequate impedance of liners.