不均匀伴流场中螺旋桨空化的黏性流数值模拟和低频噪声预报

阐述了采用空化黏流CFD瞬态模拟和脉冲球形气泡辐射噪声理论相结合的思路在螺旋桨空化低频噪声谱预报上的应用方法。预报了全附体SUBOFF潜艇标称伴流条件下的NSRDC4383五叶大侧斜桨和某七叶大侧斜桨的片空化低频噪声谱,分析了桨叶负载和空化程度对线谱成分及其谱源级的影响。空化模拟时采用作者提出的且可信性经过验证的改进Sauer空化模型和修正SST湍流模型。噪声谱预报时空化体积由空化特征长度求取,较空泡表面球形等价假设更加合理。计算表明,七叶桨较五叶桨的确具有负载小、空化初生延迟、空化低频线谱噪声低的特征。在相同的基于航速的空化数下,非均匀进流与桨叶相互作用会明显增加线谱成分及其谱源级。在伴流、空化数和转速一定时,随着负载减小,推力、力矩和桨叶空化面积均会减小,但空化体积加速度幅度却变大,离散线谱噪声级增加且由奇次谐频为主转变为以偶次谐频为主;当仅减小空化程度时,谐频线谱成分明显被抑制,且1 kHz频率处谱源级减小2.54 dB。较完整地构建了螺旋桨空化水动力和噪声性能评估的数值平台,可用于指导艇尾低噪声桨的数值设计。 

Propeller cavitation viscous simulation and low-frequency noise prediction with non-uniform inflow

Aiming at ship propeller's cavitation low-frequency noise spectrum prediction,a hybrid method combining the cavitation viscous unsteady simulation with the pulsating spherical bubble radiated noise theory was proposed. Then,both of the NSRDC4383 5-bladed propeller and a 7-bladed highly-skewed propeller's cavitation low-frequency noise spectrum subjected to the full appended SUBOFF submarine's nominal wake was investigated.And the effects of thrust loads and cavity extension on the discrete line spectrum frequency and its spectrum source level were analyzed at last.The improved Sauer cavitation model and modified shear stress transport turbulence model were adopted to simulate the propeller sheet cavitation along with integrated verification.The cavity volume acceleration related to the characteristic length representing the unsteady sheet cavitation extension,which was more reasonable than the spherical cavity hypothesis,was used to predict the cavitation low-frequency noise spectrum.Resultsshow that the 7-bladed propeller has the advantages of small loads,latter cavitation inception and low cavitating tonal noise indeed comparing to the 5 blades.Under the same cavitation index based on ship speed,the interaction of incoming inflow with blades will induce significantly low frequency line spectrum and strengthen its source level.Given the submarine wake,cavitation index and rotating speed,the thrust,torque and cavity area of blades will decrease with the load declining,but the fluctuated acceleration amplitude of cavity volume and the tonal noise spectrum level increases,and the discrete line spectrum components shift mainly to the even times of the BPF harmonics from the odd.If the cavitation extension lightens,the BPF harmonics line spectrum will be depressed,and the spectrum level at 1 kHz reduces 2.54 dB also.The numerical method above constructs a numerical system to measure the cavitating hydrodynamics and noise performances of the ship propellers,and can be productive for the numerical design of wake adapted low noise submarine propeller.