Study On The Efficient Numerical Prediction Methods Of Underwater Propeller Noise

Submarine is a major military combat force and an important tool in the field of engineering in China.In the current research and application of underwater acoustic stealth technology,propeller noise is the main noise source of submarines,so it is particularly important to predict it.The prediction of propeller noise mainly involves complex problems such as fluid-solid-acoustic coupling phenomenon and dynamic boundary treatment,which are difficult to deal with and hard to calculate.The hybrid simulation method can deal with the fluid-structure coupling problem well and can calculate the sound field quickly,so it is the main method to deal with the underwater fluid-solid-sound coupling problem at present.In the hybrid simulation,the computational domain is divided into the sound source region and the sound propagation region.The sound source region is simulated directly,and the sound field is calculated by the sound analogy method in the transmission region.As a mesoscopic method developed rapidly in recent years,the Lattice Boltzmann method(LBM)can efficiently deal with fluid-structure coupling and dynamic boundary,which is very suitable for the calculation of flow field in the sound source region.In the propagation region,the KFWH(Kirchhoff Ffowcs Willams-Hawkings)method has the characteristics of fast calculation of the total noise in the far field and small computation,so it is suitable for the calculation of the sound field in the far field.Therefore,the study on the highly efficient numerical prediction methods of underwater propeller noise is carried out in this dissertation using the advanced tool of LBM and KFWH.This paper firstly reviews the history and research status of LBM and KFWH methods in sound field calculation,and verifies the validity of their sound field calculation.The non-linear noise is not considered in the traditional method to calculate the sound field,and the importance of non-linear noise is verified.A new KFWH-N method is proposed to calculate the total noise containing the nonlinear noise quickly and efficiently because of the large amount of computation.In this paper,the calculation of underwater sound field and prediction of propeller noise are carried out as follows:(1)Adoption of LBM/KFWH hybrid simulation method and the direct simulation,verify the validity of the hybrid simulation method.Firstly,calculate the typical sound source in three-dimensional space,and verify that the KFWH method can calculate the sound field well.Based on this,numerical simulation of the sound field of three-dimensional underwater elliptical sphere rotation,and discuss the effect of solid modulus,rotation frequency and selection of virtual control surface on the sound field.(2)For traditional KFWH method accurately calculate the far field sound pressure need to select larger control surface calculation and calculation time is insufficient,puts forward a new improved method KFWH-N.Using the KFWH-N method to predict the sound pressure of the underwater three-dimensional elliptical sphere and propeller rotating flow noise,preliminarily verify the effectiveness of the method,and the method can improve the calculation efficiency,and discuss the solid modulus and rotating frequency affect KFWH-N method.