| The advantages of low energy consumption,long range and continuous profile mobility make the underwater glider(UG)a new ideal platform for acoustic sensors.When the UG navigates in the marine environment,the pressure of the near-wall region fluctuates subjected to the viscous force of the current,thus producing flow noise.The flow noise destroys the acoustic stealth of the glider,affects the results of the acoustic detection,and also brings noise pollution to the marine environment.Therefore,it is necessary to study the flow noise of the UG platform,investigate its mechanism and influence factors,to provide guidance for the noise forecast,denoise design,layout optimization of the acoustic sensor,and further application of the UG in the acoustic detection.Based on the LES-Lighthill equivalent sound source mixed method,the flow field and acoustic field of the glider platform were simulated taking the “Petrel” UG as the research object.From the aspects of lift and drag forces,fluctuating pressure,vorticity distribution of the fluid field,acoustic source magnitude,near-field sound pressure,and acoustic radiation properties of the acoustic field,the fluid field and flow noise performance of the main body and the appendage structures of the UG were analyzed.The effects of hydrodynamic shape,fluid velocity and attack angle of the objects on the flow noise performance of the UG were also discussed.The main achievements of this paper are as follows:(1)The fluid field and acoustic performance of the UG’s main body were obtained.The radiation power of the main body mainly concentrates at low frequencies,and the flow noise has no main frequency.The axial acoustic radiation of the main body shows a typical quadrupole characteristic.There exists weak acoustic radiation on the head,tail and the middle part of the main body,whereas the transition region is the main noise source of the UG due to its intensive acoustic energy.The axial sound directivity can be used to improve the flow noise performance of the main body.The radial sound directivity is not obvious,in which exhibits a circular symmetrical distribution.(2)The flow noise simulation method for protrusions of the UG was established.Comparing the two acoustic sensors with different hydrodynamic shapes,it is found that the resistance and noise performance of the streamlined one are better than those of the blunt one.Through analyzing the flow noise of the acoustic sensors installed in different locations on the UG,it is found that the overall sound pressure of the acoustic sensor on the former dome is maximal at the global sound pressure receiving point,the tail fin and acoustic sensor composite structure comes second,and the wing ranks the least.The tail fin can reduce the resistance and noise levels of the sensor to some extent.(3)The effects of the fluid flowing velocity and attack angle on the flow noise performance of the UG were discussed.For the main body,the variation laws of the overall sound pressure level with the fluid flowing velocities and attack angles in the axial and radial directions of the UG were obtained.Results show that the acoustic pressure increases regularly with the increase of the fluid flowing velocity and positive attack angle.The axial acoustic radiation of the main body maintains the quadrupole characteristic,but with the increase of the fluid velocity,the radiation power of the main body trends to be uniformly distributed.With the increase of the positive attack angle,the radiation region of the maximal acoustic pressure offsets in the clockwise direction.The radial sound directivity changes,and the acoustic pressure of the upper side of the main body are higher than those of the lower one.For the appendage,the sound pressure of the appendage increases with the positive attack angle.The longitudinal radiation region of the maximal acoustic pressure also offsets in the clockwise direction,the altitudinal sound directivity changes,and the radiation power trends to be uniformly distributed. |
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