Research On Drag & Noise Reduction Of Multilayer Covering Structure Under Turbulence Excitation

Being used as weapons and equipment,underwater vehicles such as submarines and torpedo have been highly valued by all countries,whose high speed performance and stealth performance are urgently demanded in order to adapt to the new international situation,thus the resistance and noise of the underwater vehicles should be greatly reduced.Therefore,the research of their cover layers with drag reduction and noise reduction has become a hot topic.In this paper,the multi-layer covering structure is chosen as the research object and its necessity and feasibility on drag and noise reduction are analyzed,then a novel cover layer with a multilayer structure is presented and the performance of the cover layer on drag and noise reduction is studied there after.This article mainly carried out the following aspects of the work:Firstly,according to the working characteristics and principles of the cover layer,the overall scheme of the three layer structure is determined,and the detailed structural design is carried out according to the functional requirements of each layer.The cover layer is mainly composed of epidermis,sound absorption layer and sound insulation layer.It can effectively reduce the fluctuating pressure and suppress the sudden phenomenon of turbulence,so as to achieve effective control of resistance and noise.Secondly,based on the bidirectional fluid solid coupling method,the Fluent software is used to simulate the turbulent field around the cover layer,and the distribution of the circumferential and longitudinal pulsation pressure around the cover layer is solved.Through the simulation analysis of drag reduction rate,wall deformation and shear stress in different working conditions,the drag reduction characteristics and internal mechanism of the cover layer are explored.Results show that the designed cover layer has better drag reduction characteristics with the mechanism that the flexible surface layer can attenuate turbulence.Thirdly,based on the FW-H equation and the boundary element method,the sound field around the cover layer is simulated by the software of the Fluent and LMS Virtual.Lab,and the sound field distribution of the flow noise and the flow-induced noise around the cover layer is solved,then the parameters of the acoustic field nephogram and its various directions are obtained.Through theoretical analyzing of the noise reduction characteristics around the cover layer under different working conditions,the noise reduction characteristics and its inner mechanism are explored.Results demonstrate that the cover layer can restrain the growth of vortices in the turbulent flow field,reduce the generation of the flow noise,and repress the vibration of the shell surface,thus the generation of the flow-induced noise is suppressed.Finally,the acoustic characteristics model of the cover layer is established by adopting the waveguide finite element transfer matrix method and the acoustic characteristics model is simulated through COMSOL software.Taking the sound absorption performance as the index,the simulation analysis is carried out,where the influence principles of the cylinder cavity,the round platform cavity and the material parameters on the acoustic characteristics is simulated.Results show that the cover layer has good effect on sound absorption at low frequency with wide bandwidth.In the paper,a novel multi-layer covering structure of underwater vehicle is presented,and its drag reduction,noise reduction and acoustic characteristics are studied and analyzed.Results show that the designed cover layer not only has better acoustic performance,but also can achieve drag reduction and noise reduction effectively.Therefore,it can provide a reference for future research of underwater vehicle skin.