Study On Vibration And Noise Characteristics Of Large Skew Elastic Propeller

Seven-blade highly skewed propeller is the mainstream propeller of submarine,and its underwater vibration and noise characteristics are important factors affecting the acoustic stealth of submarine.In this thesis,a seven-blade highly skewed propeller is taken as the research object,and the propeller is regarded as an elastic body.The two-way fluid-solid coupling method is used to analyze the vibration characteristics of the propeller under water,and the difference between the hydrodynamic performance of the rigid propeller and the elastic propeller is compared.Based on the fluctuating pressure on the blade surface in the time domain as the rotating dipole sound source,the noncavitating low-frequency noise of the propeller is calculated by Fourier transform and acoustic software LMS Virtual.Lab.The main contents are as follows :(1)The open water performance curve of the AU-type four-blade propeller is calculated by the unsteady Reynolds-averaged SST k-ω model and the sliding mesh technique.The results are in good agreement with the existing experiments.Then,based on the above method,the hydrodynamic performance of the seven-blade highly skewed propeller is calculated,and the difference in hydrodynamic performance between the rigid propeller and the elastic propeller when the advance coefficient J = 0.2 is compared and analyzed.Compared with the rigid propeller,the thrust coefficient and torque coefficient of the elastic propeller decrease,while the velocity value at the blade tip increases slightly.In addition,the pressure distribution on the surface of the elastic blade is more disordered and prone to deformation.(2)The dry and wet modes of the seven-blade highly skewed propeller are compared.Under the influence of attached water mass,structural damping and stiffness,the natural frequency of the propeller in water decreases more.In addition,the main vibration modes of the propeller are three types : axial vibration,axial disturbance and the combined motion of the first two types.In the time domain,the vibration characteristics of each position of the blade are basically the same,and the maximum deformation occurs in the propeller shaft direction.By analyzing the structural performance,it is found that the blade deformation mainly occurs at the tip of the blade,and the maximum stress is located in the middle and root of the blade.Therefore,in the design of propeller machining,the bearing strength of blade root and the displacement deformation of blade tip should be considered.(3)The spectral characteristics of the sound pressure level of the propeller at different field points in the 5 ～1000 Hz frequency band are analyzed.It is found that the peak points of the spectrum are mainly located at the shaft frequency,blade frequency and natural frequency points of the propeller.The sound pressure level attenuation characteristics of the propeller along the axial and disk directions are analyzed by dimensionless distance.It is found that the sound pressure level in the wake direction of the propeller is much higher than that in other directions,which is easy to be detected by enemy sonar.The directivity of the far-field radiated sound pressure of the propeller is mainly in the shape of ’ 8 ’,and the angle of ’ 8 ’ is different at different frequency points.In addition,the near water surface will affect the sound pressure directivity of the propeller in the far field,and as the propeller is closer to the water surface,the radiated noise is smaller.(4)In the actual work of the propeller,the wake field of the submarine structure has a great influence on the propeller.In this thesis,the low-frequency acoustic radiation characteristics of the submarine structure under water are calculated to prepare for the coupling radiation noise of the submarine-shaft-propeller.It is found that due to the shape and size of the submarine structure,when studying the acoustic radiation characteristics of the submarine structure,the sound field radiated within 1500 m cannot be directly approximated by the point source radiation sound field.In addition,the directivity of submarine radiated sound pressure is obvious in the bow and stern direction,which is consistent with the maximum radiated sound pressure level in the direction of propeller wake field.