The Suppression Of The Hydrodynamic Noise From Underwater Sonar Domes By Flow Control Technique

The sonar dooms avoid the direct effect of turbulent pressure fluctuations on the sonar,but the hydrodynamic noise caused by the fluid-solid coupling of the water medium and the sonar dooms during the ship’s navigation.At high speed,the hydrodynamic noise of the crotch increases a lot.The background noise affects the signal-to-noise ratio of the sonar array.This paper conducts research on the suppression of hydrodynamic noise in sonar dooms,and proposes four flow control methods to suppress the flow-induced noise of the sonar doom model under incoming flow excitation.We used the numerical analysis and post-processing methods to analyze the flow characteristics and flow-induced noise characteristics of the sonar doom model.We found that the total pressure at the stagnation point of the leading edge of the sonar doom was the largest.As the flow velocity increases,the pressure gradually decreases,and the flow state is laminar.When the incoming flow passes through the maximum cross-section of the doom,the flow velocity reaches the maximum,after which the flow separates.The fluid flows through the tail of the model and cavitation occurs when it leaves the structure,resulting in a shedding vortex.Based on this,an effective flow control technology is sought to control the unstable flow of the sonar dooms to suppress the flow-induced noise of the sonar dooms.Four flow control technologies are used: serrated leading edge,serrated trailing edge,miniature vortex generator,and suction current.The results show that with the sawtooth turbulence at the leading edge,the transition of laminar flow to turbulence is advanced,and more small vortices are generated in the transition area,which suppresses the turbulent pulsating pressure on the model wall.With the effect of the trailing edge sawtooth,when the sawtooth scale is close to the trailing vortex scale,the turbulent pulsation caused by the trailing vortex can effectively restrain the model tail.With the turbulence of the miniature vortex generator,the vortex is broken in the transition area,and a large number of small vortices are generated,which avoids the low-frequency noise caused by the large vortex.The suction control decomposes the pressure at the leading edge,which greatly reduces the back pressure gradient in the transition area of the doom,thereby delaying the separation of the boundary layer and suppressing the flow-induced noise caused by the separation vortex on the model excitation.In these control technologies,the micro-eddy current generator has a significant noise reduction effect and the volume of the micro-eddy current generator is small,the shape of the sonar dooms is basically not changed,so it has little effect on the sonar detection performance in the sonar dooms.Therefore,the correlation between fluid resistance and flow-induced noise in a miniature vortex generator model is analyzed.We find that the noise reduction effect and drag reduction effect of the miniature eddy current generator have a positive correlation.Although the eddy current generator will directly cause the model to experience greater pressure differential resistance,the flow state of the boundary layer behind the model with the eddy current generator turned into turbulent flow.This increases the static pressure on the wall of the rear model,reduces the pressure difference between the front and the rear of the model,thereby reducing the flow resistance,and offsetting the resistance-increasing effect caused by increasing the area facing the flow.The flow control technologies proposed in this article provide corresponding technical support for reducing the hydrodynamic noise of the real ship dooms.Since these technologies are developed for the flow control of the existing sonar dooms,these flow control technologies are more suitable for engineering application needs.Since the micro-eddy current generator has minimal changes to the sonar dooms,it provides a new idea for the hydrodynamic noise control of the sonar dooms of the high-speed ship.