Abstract
The hydrodynamic noise from the horseshoe vortex can greatly destroy the acoustic stealth of underwater vehicles at low frequency. We investigated the flow-induced noise suppression mechanism by mechanical vortex generators (VGs) on a SUBOFF model. Based on the numerical simulation, we calculated the flow field and the sound field of the three shapes of mechanical VGs: triangular, semi-circular, and trapezoidal. The triangular VGs with an angle of 30° to the flow direction achieved a better noise reduction. The optimum noise suppression is 8.93 dB, when the distance from the triangular VGs to the sail hull’s leading edge is 0.1c, where c is the chord length. The noise reduction mechanism is such that the mechanical VGs can destroy the formation of the horseshoe vortex at the origin and produce counter-rotation vortices to weaken its intensity. We created two steel models according to the simulation, and the experimental measurement was carried out in a gravity water tunnel. The measured results showed that the formation of the horseshoe vortex could be effectively inhibited by the triangular VGs. The results in our study can provide a new method for hydrodynamic noise suppression by flow control.
Highlights
The noise sources of a submarine can be categorized into propeller noise, hydrodynamic noise, and mechanical noise
When the fluid flows around the surface of the submarine, the turbulent fluctuation pressure produces and radiates self-noise, which is known as the flow noise
Since the placement of triangular vortex generators (VGs) is related to the generation of the lateral vortices, which the placement triangular is related thethe generation of theoflateral vortices, which can Since negatively influenceofthe intensityVGs at the origin to and running path the horseshoe vortex, can influence the intensity and theofrunning thealso horseshoe the thenegatively distance from the triangular
Summary
The noise sources of a submarine can be categorized into propeller noise, hydrodynamic noise, and mechanical noise. The turbulent fluctuation pressure excites the elastic shell of the submarine to vibrate and radiate another noise, known as the flow-induced noise. With the development of advanced technologies, some models have been proposed to calculate the flow field of VGs. For instance, Törnblom explored VG control of parameter variations at a low computational cost [20]. Only Manshadi [33] found that mid-VGs could significantly reduce the cross-flow separation and the drag force, but the author did not consider the hydrodynamic noise. The flow control reports on VGs in the air cannot be directly used to reduce the hydrodynamic noise. Since VGs can be used to redirect the flow in the aerodynamic field, we proposed the idea that mechanical VGs can be applied to reduce a submarine’s flow-induced noise through the proper flow control. The results from our study can provide a new way to reduce the hydrodynamic noise and enhance the acoustic stealth level of underwater vehicles, such as submarines, torpedoes, unmanned underwater vehicles (UUVs), etc
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