水下物体脉动压力与流噪声频谱特性的研究

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.

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。

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。本项目应用大涡模拟理论，通过求解非定常不可压缩的Navier-Stokes方程，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，通过与潜艇模型脉动压力的试验结果比较分析表明，大涡模拟理论成功地模拟了潜艇壁面脉动压力的频谱变化，结果具有较可靠的精度。传统的流噪声计算一般以FW-H方程为基础，但由于该方程在推导过程中引入了紧致声源假定，故其只能计算远场中的声学信息，对潜艇壁面与近场则无能为力。本研究以前面得到的粘性流场作为声源，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，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，计算分析水下航行体辐射噪声的频谱范围和指向性。在此基础上对操纵运动中水下航行体粘性流场与流噪声，流固耦合作用下的流激噪声，螺旋桨噪声及柔性材料的减阻降噪等相关问题进行了初步研究。这些研究对进一步揭示旋涡、湍流、声波等相互作用的机理有着深刻的理论意义，解决了流场和声场数值模拟所面临的关键问题，搞清了湍流边界层辐射噪声源中的脉动压力与流噪声的关系，发展了有实用价值的理论方法和计算软件；从实用价值上看，对指导新型安静型潜艇的设计和提高我国潜艇的作战性能、隐蔽能力具有重大的现实意义，同时为探测分析敌方潜艇的频谱特性提供了有效的手段。在学术和理论发展上达到目前国际前沿发展水平。