喷水推进器进水流道的声传播特性分析

进水流道作为喷水推进泵脉动声源通过进水口向远场辐射的传递通道,声波经流道传播后流道进口处声压峰值频率相对流道出口声压峰值频率发生较为显著的偏移。为解释该现象,文章以进水流道为对象分析其声传播特性。首先分别利用阻抗出口边界和自动匹配层出口边界计算分析了轴对称变截面管道的声传播特性,计算值与文献值吻合较好,验证了大截面管路声传播特性数值计算的可信性。然后以进水流道为对象,并以面平均声压衰减量为评价流道声学特性的指标,利用自动匹配层出口边界分析了流道的声传播特性。结果表明:由于低频段流道内仅能传递平面波,高次波被衰减,导致该频段声压衰减量较大;声压衰减量的最小值对应频率与喷泵叶频或其谐频接近,使得流道进出口截面处最大声压对应频率产生偏移。

Sound propagation characteristic analysis of waterjet duct

As the sound transmission channels of pulsating sound source of waterjet pump to far field, the frequency corresponding to the biggest pressure at duct inlet will shift notablely compared to the frequency corresponding to the biggest pressure at duct outlet when the sound wave propagate in duct. In order to ex-plain this phenomenon, the duct is taken as the object to analyze its sound propagation characteristic. The impedance boundary and AML boundary at pipe outlet is used to analyze the sound propagation of axis symmetric variable area pipe, the simulation result is well in agreement with the result from reference, and the reliability of the simulation of sound propagation in big section pipe is validated; Then the duct is taken as the object and the reduction of averaged sound pressure level of area is utilized to evaluate the sound transmission characteristic of duct with AML boundary at inlet. The results show that only plane wave can propagate in duct in low frequency and the high order wave will attenuate which can lead to bigger noise reduction; When the frequency corresponding to the smallest noise reduction of duct is close to the blade passing frequency or harmonic of blade passing frequency of waterjet pump, there is an excursion between the frequencies of biggest pressure at inlet and outlet of duct.