基于LES与Powell涡声理论的孔腔流激噪声数值模拟研究

孔腔流动中含有复杂的流体振荡,不但能够引起明显的噪声,而且会造成物体脉动压力和阻力的急剧增加,因而孔腔流动与流激噪声已经成为流声耦合研究领域的重要内容。文章首先对于Powell涡声理论进行了介绍,给出了涡声方程及其求解的详细推导过程,随后利用圆柱/机翼组合体与方腔流激噪声测试结果验证了计算方法的可靠性,最后采用大涡模拟方法结合Powell涡声方程数值计算了两型孔腔在不同水速下的流激噪声,并与中国船舶科学研究中心循环水槽试验结果进行了对比分析,结果表明数值计算方法能够较准确地预报孔腔流激噪声,并能展示孔腔内外涡旋结构。计算结果表明:在500 Hz以下的低频段,格栅1型孔腔的流激噪声显著高于格栅2型孔腔;在500 Hz-10 k Hz高频段,格栅2型孔腔流激噪声比格栅1型孔腔高,但随着流速的增高,两种孔腔流激噪声在高频段的幅值基本一致。这些现象与孔腔内的涡旋结构密切相关。文中对孔腔流激噪声的数值预报方法进行了验证,有益于理解孔腔非定常流动的物理机理,且为抑制孔腔流激噪声奠定了基础。

Numerical simulation on the flow induced noise of cavity by LES and Powell vortex sound theory

Lots of fluid oscillations are contained in the cavity flow, which can induce obvious noise and in-crease pressure fluctuations and resistance of vehicle. Thus, cavity flow and flow induced noise have become two important issues in the flow-acoustic coupling field. In this paper, the mathematical model and physi-cal meaning of Powell vortex sound theory are analyzed and elucidated. The flow induced noise of rod-air-foil and rectangular cavity are computed and compared with the measurements to validate the numerical method. And, the flow induced noise of two cavities (two shapes of baffles) under different velocities are computed by LES and Powell vortex sound equation. The computed results are compared with experimental data in Large Circulation Channel in CSSRC. The computed results indicate that the flow induced noise of cavity with baffle1 is obviously higher than that of cavity with baffle2 in the low frequency (<500 Hz); the flow induced noise of cavity with baffle1 is lower than that of cavity with baffle2 in the high frequency (500 Hz~10 kHz), but they are close to each other in the high frequency as the water speed increasing.These phenomena are in close relationship with vortex structure in cavity. It shows that the numerical simu-lation method is credible. These works are beneficial for understanding the physical mechanism of unsteady flow around cavity and lay a foundation for suppressing flow induced noise by flow control approach.