Objectives In order to reduce the flow noise on the outer surface of the traditional circular sonar, three sonar shapes (circular, elliptical and square) are proposed, and the hydrodynamic characteristics and flow noise on their outer surfaces are studied.
Methods Based on the standard
k - \varepsilon 
turbulence model in Fluent and Lighthill's acoustic analogy method, the flow field and sound field of the outer surfaces of three alternative sonars are analyzed.
Results Comparing the hydrodynamic results of the three sonar shapes, it is found that the square has the largest lift coefficient amplitude and average drag coefficient, and the ellipse has the smallest. The hydrodynamic diversity is caused by the differences in the boundary layer separation points and wake vortex. Comparing the flow noise results, it is found that the total sound pressure level of the circle is the largest and that of the ellipse is the smallest. The circle and square show the characteristics of a "positive figure eight" dipole sound source, and the maximum sound radiation is perpendicular to the incoming flow direction, while the ellipse shows the characteristics of an "inverted figure eight" dipole sound source, and the maximum sound radiation is horizontal to the incoming flow direction.
Conclusions This study can provide references for the shape design of sonar, e.g., replacing the traditional circular sonar with the elliptical sonar.
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