Numerical Simulation And Experimental Study Of Non-cavitation Line-spectrum Noise Of Underwater Counter-rotation Propeller

With the increasing of performance improvement and navigation depth, Counter-rotation Propellers which are important propulsion device for underwater vehicle often work in non-cavitation condition. It has important practical significance for identifying underwater targets to study the mechanism and characteristics of non-cavitation line-spectrum noise of underwater counter-rotation propeller. This paper firstly analyzes the mechanism of non-cavitation line-spectrum noise of counter-rotation propeller, and then numerical simulation method was used to compute the non-cavitation line-spectrum noise. Finally, experimental measurement was used to verify the reliability of the theoretical analysis and numerical simulation.Firstly, this paper analyzes the mechanism of non-cavitation noise line-spectrum frequency of counter-rotation propeller. The mechanisms are interference effect and circumferential harmonics field effect. The unsteady force on the blade was used to described the two mechanisms which was treated as the primary noise source. According to the generalized acoustic analogy equation, the far field sound pressure expression is presented. The line-spectrum frequency and the directionality of sound pressure have been analyzed. The results show: the predication line-spectrum frequency could be written as f=s APF+m BPF1+n BPF2, sound pressure radiation was “8”-shaped distribution.Then, the numerical simulation platform has been built to predict the non-cavitation line-spectrum noise of underwater counter-rotation propeller. The unsteady flow field was simulated finely in the first, and then the sound source was captured in the fine flow field which was treated to noise computation. The counter-rotation Propeller has been calculated the hydrodynamic performance in steady flow and unsteady flow. The best turbulence model has been chosen by using four turbulence models to calculate the hydrodynamic performance in steady flow which was RNG k-ε turbulence model. The sliding mesh has been used to calculate the hydrodynamic performance of counter-rotation propeller. Compared to the result of steady flow, the result of unsteady flow by sliding mesh is closer to the experimental. The distribution of pressure, velocity and wake flow of counter-rotation propeller has been analyzed. After reaching the quasi-stable state, the capturing of noise source in unsteady flow was begun, and then the noise calculate was begun. The overall sound pressure level, sound pressure level in 1/3 OCT and sound pressure level curve has been calculated.Thirdly, the experimental measurement has been carried out in 03 B cavitation tunnel. The experiment results of overall sound pressure and sound pressure in 1/3OCT in 800Hz-10 k Hz agree well with numerical simulation. The DEMON processing method has been used to extract the low-frequency modulation of line spectrum. The line-spectrum frequency agreed well with line-spectrum theory prediction formula and calculation results. The experimental results verify the accuracy of theoretical line-spectrum prediction formulas and the reliability of numerical simulation platform.Finally, the numerical simulation platform has been used to calculate the non-cavitation noise of counter-rotation propeller and single propeller in a typical operating condition and the qualitative and quantitative analysis has been made. The result showed that unsteady pressure fluctuation in blade was the main noise source in non-cavitation condition. The SPL trends result shows that the overall sound pressure level increases first and then decreases slowly at the radial direction. With the increase of axial distance, the overall sound pressure decreases slowly. The directional sound pressure level could obtain by arranging circle array measurements, the result was “8” shape distribution which was consistent with the theoretical analysis. The line-spectrum frequency of sound pressure agreed well with theoretical formula. The result often show that SPL over time into a normal distribution. The result of single propeller shows that the line-spectrum is much less than counter-rotation propeller.