The Suppression Of Hydrodynamic Noise From Underwater Cavities By Flow Control

Many underwater vehicles need the techniques of noise control.Especially for the submarines,the control of radiated noise is the fundamental guarantee of survivability and combat effectiveness.The hydrodynamic noise is one of the three major noises of the navigators.At high speed,the hydrodynamic noise becomes the main noise,which must be paid more attention to.The noise from the cavity is an important part of the hydrodynamic noise of underwater vehicles.It is of significance to study the reduction of the cavity noise.The disertation proposes three new techniques of the flow control for noise reduction: the dimples in the leading-edge of the cavity,the chamfers in the trailing-edge of the cavity,and the deflectors in the trailing edge of the cavity.The numerical simulation of the flow field and the sound field are combined to calculate the effect of these flow control techniques on the hydrodynamic noise of the cavity,based on the general large eddy simulation,Lighthill acoustic analogy and finite element.The application of the numerical simulation method is validated by the calculation of the flow-induced noise from the simple plate and the flow noise from the valve in the steam line in the literature.The underwater three-dimensional cavity's hydrodynamic noise of three flow control techniques and no-flow control techniques are calculated.The data of the sound field and the flow field are analyzed.The results show that all three techniques can inhabit the hydrodynamic noise of the cavity.The dimples can reduce the noise in the whole frequency band,but the noise reduction effect is determined by the dimples' diameter and the aspect ratio;the chamfer can reduce the high frequency noise,but the noise reduction effect depends on the chamfer's angle and line type;the deflectors can reduce the low frequency and high frequency noise,while the noise reduction effect is affected by the angle of the flow inlet and the arrangement of the deflectors.In order to validate the noise reduction of these flow control techniques,the radiated sound power of the three-dimensional cavity with and without flow control techniques is measured by the reverberation method in a low-noise gravity water tunnel.The experimental results are in good accordance with that of the numerical simulation.Then,the flow control techniques proposed in the dissertation can inhabit the hydrodynamic noise from the cavity at a variety of flow velocity.The results in this dissertation can provide some reference for the suppression of the hydrodynamic noise,especially the cavities in the submarines.