Forward sound scattering from an underwater vortex

The vortex scattering is due to the flow-sound interaction.Studying this problem is important for target detection or flow field acoustic tomography.A numerical model of forward acoustic scattering from an underwater vortex at low Mach number is established,and form functions and sound directivity of vortex scattering are evaluated.First,the acoustic scattering model considering the flow-sound interaction is given based on the acoustic perturbation theory,which is solved by using the finite-difference time-domain method with perfectly matched layers as the absorbing boundary condition.After the code is validated,effects of flow intensity on the scattering amplitude are analyzed when the Gaussian vortex core size is 1 m to 10 m and the dimensionless incident wave number is 1 to 10.Simulations indicate that the form functions of the acoustic scattering field is symmetrical and of obvious directivity at low Mach number,and increases with the increase of the incident wave number,the size of the eddy core,or the intensity of the eddy flow.As the wave number increases,the direction of the main peak gets more closely to the propagation direction of the incident wave.