伴流场中对转桨空化初生的判定与辐射噪声预报和校验

采用空化多相流瞬态模拟和边界元数值声学计算相结合的混合方法,预报了全附体假尾后对转桨在初生空化状态下的线谱和宽带谱噪声,分析了初生空化状态下对转桨噪声谱级相对于无空化状态的增量,提出了同时从流场与声场角度判定对转桨空化初生的四个充分条件。预报值与空泡水筒噪声测量值进行了比较。多相流瞬态模拟包括非定常雷诺时均模拟、尺度适应模拟和分离涡模拟三种方法。计算结果表明,在大范围进速系数范围内预报对转桨敞水性能曲线与测量值吻合很好。尺度适应模拟(SAS)和分离涡模拟(DES)在捕捉对转桨空化脉动压力时精度相当,均能满足非定常负载噪声预报的精度要求;雷诺时均模拟(URAN S)仅对于低频负载噪声来说基本适用。空泡体积脉动诱导线谱噪声在800 Hz处的预报误差小于4 dB;在800 Hz^3 kHz频段内,预报得到1/3oct中心频率处谱级的平均误差小于1.5 dB,总声级预报误差小于2.4 dB。空化初生的充分条件为:空化面积与桨盘面面积的比值小于2%、积分力和叶梢截面压力系数分布较无空化状态基本不变且中高频段噪声谱级增加8~10 dB。较好地解决了伴流场中对转桨空化初生判定和初生空化状态下辐射噪声预报的两个技术难题,可直接服务于高速、低噪声鱼雷的设计研发。 

Numerical prediction of cavitation inception radiated noise of contra-rotating propeller with non-uniform inflow

Cavitating inception tonal components and broadband noise of a contra-rotating propeller in the behind-tail condition are predicted numerically by the hybrid method and validated by cavitation tunnel test. The multiphase flow transient simulations, including unsteady Reynolds-averaged Navier-Stokes (URANS) method, scale-adaptive simulation (SAS) and detached eddy simulation (DES), are used to calculate the fluctuated cavity volume and fluctuating pressure on both fore and aft propellers that acting as main noise sources. The pulsating spherical bubble radiated noise theory and directly boundary element numerical acoustics are adopted to obtain the cavitation noise spectrum. In this process, both the effects of calculational precision of source fluctuations in the flow on noise prediction and the cavitation inception on propeller noise are investigated. Besides, four sufficient conditions to determine the cavitation inception are put forward initially. Results show that, the predicted open water performances agree very well with the experimental data over a big region of advance ratios. Tile SAS presents a comparable ability to DES to predict the fluctuating pressure of contra-rotating propeller, and then serves satisfactory to unsteady load noise prediction, whereas the URANS is slightly less but still being appropriate for the low frequency noise. The prediction error of line spectrum in 800 Hz induced by fluctuated cavity volume is smaller than 4 dB, and the averaged error of spectrum level in each 1/3 Octave band is less than 1.5 dB in the region of 800 Hz to 3 kHz associated with being smaller than 2.4 dB for the total sound pressure level. A ratio less than 2% of the cavity area to disk plane of fore propeller, in conjunction with the global force variables and pressure coefficient distribution around the tip section nearly unaltered compared to that of non-condition, and the increase of noise spectrum about 8-10 dB in the mid and high frequency areas can be used to determine the cavitation inception considering both the visualand acousticcriteria at the same time. Based on this research, the two technical challenges concerning cavitation inception determination and the inception noise prediction for contra-rotating propeller in wake have been overcome, which can be greatly benefited to new torpedo design with high speed and low noise.