开孔结构流致噪声的数值模拟和机理分析

飞机机体表面的开孔设计会形成空腔结构，产生空腔流致噪声。空腔噪声的控制需要彻底认识其流动和噪声机理。以飞机的功能性开孔为例，通过半经验公式分析了其空腔噪声频率随速度的变化规律，预测了出现流声共振的工况。空腔发生流声共振时，特定频率的纯音噪声会被放大。为此，采用脱体涡模拟方法开展了开孔结构流声共振的三维非定常数值计算，分析了其流场和声场特性。其中，数值方法的准确性通过圆形空腔标模计算进行验证。结果表明，在一定速度下剪切层内的扰动将诱发空腔深度方向声模态，出现流声共振现象。此时，剪切层表现为强烈的周期性上下拍动，空腔底部和后缘区域的局部压力脉动幅值较大，声波主要由空腔后缘向上游方向辐射，上游噪声大于下游。

Numerical simulation and mechanism analysis of flow-induced noise in open-hole structure

The open-hole on the surface of the aircraft body creates a cavity, it will generate cavity flow-induced noise. The control of cavity noise requires a thorough understanding of its flow and noise mechanism. Taking the functional opening of an airplane as an example, the variation of cavity noise frequency with speed was analyzed using semi-empirical formula methods, and the occurration of flow acoustic resonance phenomenon was predicted. When the flow acoustic resonance phenomenon occurs, the tonality at a specific frequency will be amplified. For this reason, detached eddy simulation (DES) method was used to simulate the open-hole structure with a three-dimensional unsteady simulation, the flow field and sound field were analyzed. And the accuracy of the result was verified by calculating the standard circular cavity. The results showed that under certain conditions the disturbance in the shear layer will induce the depth acoustic mode and flow acoustic resonance will occur. At this time, the shear layer exhibits strong periodic up-and-down flapping. The large areas are the bottom and the trailing edge of the cavity, and the sound waves radiate upstream from the trailing edge of the cavity, upstream noise is greater than downstream.