Analysis On The Characteristics Of The Fluid Radiated Noise Of The Flexible Rudder Of The Naval Vessel

The noise around the ship rudder body is an important part of its noise source.In order to study the noise reduction characteristics of the flexible rudder of ships,analyze its noise reduction mechanism and reveal the influence of the elastic trailing edge structure parameters of the rudder body on the noise reduction effect,the article uses the method of noise mixed prediction to calculate the flow radiation around the rudder body under different working conditions Sound field.For the NACA0018 airfoil rudder body,the large eddy simulation turbulence model is used to calculate the circumfluence flow field,and the sound source data obtained from the circumfluence flow field calculation is used to calculate the radiated sound field through acoustic analogy theory.In order to analyze the noise reduction mechanism of the flexible rudder,the paper developed a structural field-fluid field coupling field calculation model.The model adopts the dynamic mesh control method based on the diffusion principle and the slow acceleration convergence algorithm of sub-relaxation to calculate the flexible trailing edge rudder The flow field around the flow and its radiated sound field.In order to reveal the influence of the structural parameters of the elastic trailing edge of the rudder body on the noise reduction effect,the flow field around the flexible rudder under different damping coefficients and elastic moduli was calculated,and the radiated sound field was calculated by the convective FW-H integral equation.The radiated noise is refined to study the influence of structural material parameters on the noise around the flow and the correlation of the corresponding noise items.By comparing the flow field around the rudder body at different angles of attack,it is found that as the angle of attack increases,the transition point of the boundary layer on the suction surface of the rudder body gradually moves upstream and the thickness of the boundary layer gradually increases,while the thickness of the pressure surface boundary layer gradually decreases.The vortices generated in the turbulent boundary layer on the suction surface and the pressure surface alternately fall off.In this process,the wall pressure pulsation is accompanied by the wall pressure pulsation frequency decreases as the angle of attack increases.By comparing the flow field around the rudder body under different incoming flow speeds,it is found that as the flow speed increases,the transition point of the rudder body wall boundary layer gradually moves downstream,the thickness of the turbulent boundary layer gradually decreases,and the wall pressure fluctuation frequency increases.The deformation of the flexible trailing edge increases with the increase of the flow velocity.This deformation effectively reduces the flow separation on the wall surface,inhibits the flow separation on the wall surface of the rudder body,and reduces the radiation noise caused by the wall pressure pulsation.However,the noise caused by the deformation and swing of the flexible trailing edge can also not be ignored.Through the acoustic analogy theory,the convective FW-H integral equation is used to calculate the sound field radiated by the flow around the rudder body.The flow noise around the rudder body has a dipole characteristic.As a whole,the flow noise of the flexible rudder is smaller than that of the rigid rudder,and it has a certain noise reduction effect.It should be noted that the total sound pressure level of flexible rudder noise near0° and 180°(that is,the direction coincides with the chord direction of the rudder body)is slightly higher than that of rigid rudder noise.In addition,the flow noise around the flexible rudder exhibits dipole characteristics but does not strictly take the chord direction of the rudder body as the symmetry axis,which is caused by the deformation of the flexible rudder trailing edge and its nonlinear fluctuations.Through the analysis of the frequency spectrum characteristics of the flow noise,the flow noise is composed of load noise and thickness noise,and the load noise related to the wall stress tensor is the main component.In addition,the main frequency for the flexible rudder to reduce noise is in the high frequency band,mainly in the frequency band above 1000 Hz.For low frequency noise,the amount of noise reduction is not obvious.By calculating the sound field radiated by the flow around the elastic trailing edge with different damping coefficients,it is found that as the damping coefficient increases,the flow noise of the rudder body gradually decreases,but the reduction is not obvious,all within 2d B.In the flow around noise,the load noise occupies its main component,which has a dipole characteristic,while the thickness noise has a monopole characteristic,and the load noise is about twice the thickness noise.The load noise and thickness noise under different damping coefficients have certain differences mainly in the high frequency range,but their discrimination is low.The increase in the damping coefficient reduces the rms value of the lateral displacement of the flexible trailing edge.Its spectral characteristics show that the differentiation of the lateral vibration of the flexible trailing edge under different damping coefficients is mainly reflected in the high frequency band with a frequency higher than 1500 Hz,which is different from the far-field term of the sound field around the flow.The impact trends are consistent,indicating that the deformation of the flexible trailing edge is related to the far-field term of the surrounding sound field.By calculating the radiated sound field of the circumfluence under different elastic modulus of the elastic trailing edge,it is found that as the elastic modulus increases,the circumfluence noise of the rudder body gradually decreases,but the reduction is not obvious,all within 2d B.The sound pressure level spectrum structure of thickness noise is similar under different elastic modulus,but the amplitude has a certain degree of discrimination.This phenomenon is reflected in the near-field and far-field terms of thickness noise.The increase of the elastic modulus reduces the rms value of the lateral displacement of the flexible trailing edge.Its spectral characteristics show that the spectral structure is similar under different elastic moduli but the amplitude is somewhat distinguishable.This is consistent with the thickness noise change trend,indicating that the flexible trailing edge The deformation of is correlated with the thickness noise term of the flow noise.