Abstract
Loud hydrodynamic noise is not only potentially harmful to the health of organisms in the ocean, but it is also a threat to the survival of underwater vehicles. Different from the general noise reduction technologies at present, a new idea for a flow-induced noise reduction design with spanwise microgrooved surfaces inspired by sharkskin is introduced in this paper. Large eddy simulations (LES) combined with the Ffowcs Williams and Hawkings (FW-H) equation are adopted to simulate the hydrodynamic noise of the three-dimensional (3D) hydrofoil. The accuracy of the numerical predictions is checked against existing experimental data, achieving good agreement. With the increase of observing distance, the noise reduction effect at the trailing edge direction is gradually apparent, and a maximum noise reduction of up to 7.28 dB can be observed. It is seen from the noise spectra of the biomimetic hydrofoil that the main peaks are eliminated, and the noise level at high frequency is also decreased. The cause of noise reduction lies in the secondary vortex generated in the microgrooves, which hinder the process of turbulence, consume the energy of the flow, and weaken the intensity of turbulent burst. The results of this study provide a new way to design low-noise underwater structures with hydrofoils.
Highlights
Hydrofoil or airfoil is an important structure applied in many underwater devices, ranging from the sail hulls of submarines and the flapping wings of underwater vehicles to ocean turbines and marine propellers
Noise originates from various sources on these devices, such as (1) the self-noise of airfoil generated by the interaction of boundary layers and the wake and (2) the noise caused by cavitation of some ocean engineering applications, for example, marine propellers
Large Eddy Simulation Model Turbulence is the three-dimensional unsteady random motion observed in fluids at moderate to high Reynolds numbers [47]
Summary
Hydrofoil or airfoil is an important structure applied in many underwater devices, ranging from the sail hulls of submarines and the flapping wings of underwater vehicles to ocean turbines and marine propellers. Noise originates from various sources on these devices, such as (1) the self-noise of airfoil generated by the interaction of boundary layers and the wake and (2) the noise caused by cavitation of some ocean engineering applications, for example, marine propellers. Inspired by the wings of low-noise flying owls, Howe [7,8] theoretically analyzed the effects of serration structure in the trailing-edge of airfoil on aerodynamic noise. The noise reduction mechanism and the key parameters influencing the noise reduction effect of serrated trailing edge have been studied by a lot of scholars [9,10,11,12,13]. It is necessary to introduce fresh ideas to achieve better noise reduction
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