Abstract
Flow control based on bionics provides new research ideas for noise reduction. As one of the flow control methods, the wavy leading edge (WLE) inspired by the leading edge tubercles of the humpback whale is proposed in this paper. The hydrodynamic performance and flow noise of a National Advisory Committee for Aeronautics 0020 hydrofoil subjected to three WLEs are numerically investigated. A hybrid numerical method of large eddy simulation combined with the Ffowcs Williams–Hawkings equation is adopted to obtain the unsteady flow properties and predict the far-field noise. At a Reynolds number of 3.05 × 105, the simulation results show that the addition of WLEs can reduce the lift coefficient fluctuation but will increase the drag coefficient slightly. In addition, the WLE can reduce the OverAll Sound Pressure Level of the hydrofoil by up to 7.28 dB. The analysis of the flow features shows that the WLE can reduce the pressure fluctuation on the hydrofoil surface, which is directly beneficial to the noise reduction. Moreover, the WLE enhances the spanwise flow of the hydrofoil, produces streamwise vortices, and reduces the spanwise coherence coefficient at both the leading edge and trailing edge.
Highlights
With the increasing frequency of human marine activities, the problem of underwater noise is becoming more and more serious
The concept of leading edge noise reduction in foil bionics originated from the owl wing structure,2–4 but the engineering implementation and application of sharp serrated shapes have certain difficulties and limitations, so people turn their attention to the tubercle structure of humpback whale fins
The hydrodynamic results below are sampled over a time period from 0.45 to 0.675 s
Summary
With the increasing frequency of human marine activities, the problem of underwater noise is becoming more and more serious. The foil has many practical applications, including in components of rudders, vehicle appendages, and propellers, so the reduction of flow noise emission from the hydrofoil is an important research topic. The emergence of the noise reduction design concept based on biomimetic flow control provides a new research idea for noise reduction. Characters, elements, behaviors, interaction of the biologic system to provide new design ideas, working principle, and system structures for the engineering.. The concept of leading edge noise reduction in foil bionics originated from the owl wing structure, but the engineering implementation and application of sharp serrated shapes have certain difficulties and limitations, so people turn their attention to the tubercle structure of humpback whale fins. The wavy leading edge (WLE) was bioinspired by the leading edge tubercles of the humpback whale, which are believed to help the whale to execute rolls and loops under water and have attracted increasing research interest to explore potentially wide applications and benefits for aerodynamic and hydrodynamic augmentation
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