基于LES/FW-H混合方法的缩放型喷嘴空化与噪声特性研究

Research on Cavitation and Noise Characteristics of Convergent-Divergent Nozzle Based on Hybrid LES/FW-H Method

该文采用大涡模拟(LES)与Rayleigh-Plesset空化模型相结合的方法,对缩放型空化喷嘴的瞬态流场进行数值仿真研究,成功捕捉到射流场中的空泡运动和旋涡脱落过程。以包络空泡及旋涡结构的曲面为可渗透声源面,采用Ffowcs Williams-Hawkings(FW-H)声类比方法,获取缩放型喷嘴的空化噪声特性。在空化流场的分析过程中,以压力系数为空化研究参数,发现:喷嘴内部空化现象主要由剪切作用诱导的旋涡以及喷嘴喉部的文丘里效应共同引起;喷嘴外部空泡运动受旋涡所致低压区域和射流冲击作用产生高压区域共同影响。在空化噪声的分析过程中,该文建立了一种空化喷嘴涡流信号和空泡信号的分解方法,其通过监控及对喷嘴出口界面上Q_(max)的时域信号进行频域分析,可将涡流频率成分从空化流场的压力频谱中成功分离出来。

In this paper,numerical simulations about the cavitation phenomena related to a convergent-divergent nozzle are performed by adopting large eddy simulation(LES)turbulence model and Rayleigh-Plesset cavitation model.The transient physical phenomena associated with the flow field are captured,and the basic characteristics concerning the cavitation noise are also obtained through the Ffowcs Williams-Hawkings(FW-H)acoustic analogy model.By regarding the pressure coefficient as a special parameter to estimate the cavitation of flow field,it is found that the cavitation inside the nozzle is caused by a combination of the shear-induced vortex structure and the Venturi effect at the nozzle throat,and the cavitation outside the nozzle is affected by a combination of the low-pressure regions due to the vortex structure and the high-pressure regions generated by the jet impinging effect.During the analysis process of cavitation noise,a decomposition method is established for the vortex and vacuole signals of a cavitation nozzle in this paper,which can successfully separate the vortex frequency components from the pressure spectrum of the cavitation flow field by monitoring and analyzing the time-domain signal of Q_(max) at the nozzle exit interface in the frequency domain.