Numerical Simulation Of Unsteady Cavitation And Hydrodynamic Noise Of Marine Propellers

Propeller propulsion performance has always been the focus of ship engineering.As people improve their comfort indicators,the problem of propeller cavitation,pressure pulsation and noise has become a research focus in the field of ship propulsion.In view of these problems,the viscous CFD method was used to predict the hydrodynamic performance,cavitation characteristics and pressure pulsations of the propeller,and the Lighthill acoustic analogy was used to calculate the no-cavitation noise.Based on the accuracy of numerical simulation results,the effects of skews on hydrodynamics,cavitation performance,pressure pulsations and no-cavitation noise of propellers are systematically studied,which provides some reference for the design of low noise and high efficiency propellers.The 2D section of the blade was parameterized by CST method,and the high-precision expression of the free curve was realized by the sixth-order Bernstein polynomial.In order to optimize the airfoil section,the particle swarm optimization program was written in MATLAB and combined with Xfoil.At the design condition,the lift coefficient and lift-drag ratio of the optimized airfoil(Opt.foil)were increased by 11.5% and 23.6%,respectively,compared with the original NACA66 airfoil.According to the 3D geometric modeling principle of the propeller,a MATLAB script that automatically creates the space points of the blade surface is programmed.The hydrodynamic performance of the DTMB4119 was calculated by CFD method,and the calculated results were compared with the experimental data.Based on the DTNSRDC4381 propeller,three propellers with different skews were reconstructed and the hydrodynamics of the four propellers were calculated.The calculation results show that at low load conditions,the open water efficiency and the degree of skew are positively correlated.The pressure coefficient distribution at the 0.7R section shows that the maximum negative pressure peak near the leading edge increases with the increase of the skew angle,and the cavitation of the highly skewed propeller may be delayed.The positive pressure peak near the leading edge of the pressure surface gradually decreases as the skew angle increases.The cavitation of the E779 A propeller was calculated by three common cavitation models,and the influence of the number of prismatic mesh layers on the surface of the blade was studied.The cavitation pattern of different skewed propellers was studied.It was found that at the condition of J =0.5,? =2.5,as the skew angle increases,the area of the cavitation attachment area is smaller,and the cavitation area is narrower.Based on the DTMB4119 propeller,two types of propellers with the same angle of 55� but different skew patterns were reconstructed.The hydrodynamic performance and pressure pulsation characteristics of the propeller under the condition of wake flow were calculated.The results show that when considering the wake inlet,the unsteady characteristics of the propeller cavitation are strong and the cavitation patterns changes periodically;the right side cavitation of the right-hand propeller is more serious;the bubble volume of the balanced propeller is smaller;the thrust under full wetted condition is greater than the thrust at cavitation;the efficiency of the balanced propeller is higher at cavitation condition.There is no significant correlation between cavitation pressure pulsation and cavitation number.Once cavitation,the pressure pulsation amplitude of the wake does not increase with the decrease of cavitation number.The pressure signal above the blade is the 1BPF,and the 2BPF and 3BPF also have larger components.The frequency component of the pressure signal in the wake after the propeller is mainly 1BPF.At the monitoring point above the blade,the main frequency of the biased propeller is higher than that of the balanced propeller.The propeller noise of x/D=5 position after DTMB4119 was calculated by the Near wall extraction method.The calculation results are consistent with the calculations of the panel method and FW-H method used by other professors.The propeller noise attenuation characteristics and acoustic directivity are analyzed.Finally,the propeller noise of different skew is studied,and it is concluded that the skew plays an important role in the reduction of axial noise.Taking 1BPF as an example,the skew can reduce the near-field and far-field axial noise by 20.5dB and 17.8dB;The-5� skew angle at the hub and the maximum negative skew at r/R=0.5 can significantly reduce the low frequency noise level of the propeller.