水下物体脉动压力与流噪声频谱特性的研究

声呐是通过对水声信号的频谱特征进行分析来探测水下物体的, 因此预报脉动压力和流噪声波数频率谱对于水下航行体的隐身性来说非常重要。本项目将在已有研究的基础上，运用大涡模拟对水下物体周围的湍流流场进行数值模似，通过对时-空变化的流场进行统计分析，给出脉动压力的波数－频率谱，分析其迁移特性推导出迁移速度，并探讨湍流对脉动压力模式的影响。将此粘性流场作为声源，利用Lighthill声类比理论，在不做紧致声源的假定下，通过边界元法计算包括水下物体近场的水动力噪声。从湍流边界层内的瞬时脉动速度和压力直接计算湍流边界层辐射噪声，利用声场计算结果分析讨论声源项的分布和水动力噪声的特性，揭示湍流边界层压力脉动与辐射噪声之间的关系，计算分析水下航行体湍流边界层辐射噪声的频谱范围和指向性。这一研究对进一步揭示湍流与声辐射相互作用的机理有着深刻的理论意义，同时对开发设计新型快速安静性水下潜艇有着重大的现实意义。

Sonars search underwater body using analysis of frequency characteristics about signal of underwater sound, so that it is very important to predict wavenumber-frequency spectrum of pressure fluctuation and flow-induced sound. Based upon the previous our researches, Numerical simulations of turbulent flow field around underwater body are deduced with the large eddy simulation (LES) . The information of the time-space field is statistically analyzed to obtain the wavenumber-frequency spectrum of pressure fluctuation. The convection velocity can be calculated from the characteristics of the convection. The suitable model of the wavenumber-frequency spectrum of pressure fluctuation included the effect of turbulent flow structure are investigated. The flow field simulated by LES is taken as acoustic sources. Without the compact acoustic source assumptions, the hydrodynamic noise generated by imcompressible viscous flow around underwater body are computed using alternative approach that combine the boundary element method (BEM) with the Lighthill's acoustic analogy. The radiated sound are calculted directly from instantaneous velocity and pressure around turbulence bounary layer, and through the computational results of sound field, the distribution of sound sources and characteristics of their radiation sound are analyzed. The frequency spectrum and directivity of radiated sound around turbulence boundary layer of underwater body also are analyzed. The relationship between pressure fluctuations and the radiated sound is discussed. This research has particular practical significance to develop the design new noiseless type submarine and more clarify of mechanism flow induced sound radiation.