Research On Prediction Method Of Marine Propeller Non-cavitation Noise

As one of the main noise sources of ships,propeller noise can be divided into cavitation noise and non-cavitation noise according to its working state.Both of them are the main components of propeller noise although their sound production mechanism and spectrum characteristics are different.In order to further explore the mechanism of propeller non-cavitation noise and find out the interference and superposition rule between the source terms of non-cavitation noise,the prediction program of propeller noise is compiled based on FW-H equation,and the prediction of propeller noise non-cavitation noise is carried out,and the preliminary verification is carried out.The main contents of this paper are as follows:(1)Hydrodynamic performance simulation of propeller.On the basis of the fact that the velocity of sound is much larger than the velocity of flow in water,it is generally believed that the flow determines the noise,and the noise will not affect the flow.Hydrodynamic analysis is indispensable for noise prediction either by acoustic software or by program.Firstly,ANSYS-CFX is used to simulate the hydrodynamic performance of propeller in the flow field,calculate the velocity and pressure values on the surface source,and then predict the noise.(2)Propeller noise prediction based on ACTRAN.In order to study propeller noise prediction method better and verify the results of program prediction method based on FW-H equation.In this paper,the acoustic software ACTRAN is taken as an example to study its noise prediction principle and method.The study validates the irrelevance of acoustic grids in the propagation domain.It is found that the coarse grids and fine grids,and the acoustic grids with different radial and axial sizes in the computational domain have little influence on the noise prediction results.On this basis,the most appropriate acoustic grids can be selected to save computational time.(3)Research on noise program prediction method based on FWH equation.According to the aeroacoustic equation and the prediction principle of propeller noise,considering that the traditional acoustic software predicts the analog sound source,on the basis of the FW-H equation derived by Farassat,the sound generation mechanism is used to program the prediction of the sound pressure level of the propeller.Because the propeller is rotationally symmetrical,the noise of a single blade is carried out on the basis of the source program.The program of sound prediction and the analysis of the prediction results can simplify the calculation method and reduce the time cost of calculation.(4)Comparison of noise prediction characteristics of DTMB P4119 propeller.It is found that the higher the advance speed,the greater the sound pressure level of the propeller.The sound pressure level of the propeller decreases quantitatively with the increase of the distance from the observation point.According to the observation of the spectrum of sound pressure level,we can see that the noise mostly distributes in the first fifth order leaf frequency.From the directivity of the propeller sound pressure level,we can see that the total sound pressure level in the near field has a small fluctuation in the circumferential direction,and the total sound pressure level in the direction is non-directional when it is 2 D away from the propeller center.In the program prediction of propeller noise based on FW-H equation,the prediction results of radial plane sound pressure level are compared with those of ACTRAN,and the directivity of downstream axial plane sound pressure level and sound pressure level is analyzed.According to the comparison of the results,we find that the program prediction method of noise is feasible.(5)Noise analysis of propeller in different zones.According to the structure of the propeller,the propeller is divided into sections.It is found that the blade surface,the leading edge and the trailing edge of the propeller contribute more to the noise of the propeller than the tip,and they are the main noise sources.In the aspect of directivity,the directivity of propeller blade,leading edge and Y-Z plane along the side is "8".The sound pressure level in the radial direction is lower and that in the axial direction is higher.The sound pressure level distribution along the blade surface,leading edge and circumferential direction of the X-Y plane propeller is almost constant,showing no directivity.