2021/01/23 by Nathan Wagenhoffer, Keith W Moored, Wagenhoffer, Nathan +5
Engineering · Physics and Astronomy · #Aerodynamics and Acoustics in Jet Flows #Aerospace Engineering and Energy Systems #Biomimetic flight and propulsion mechanisms #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #physics.flu-dyn
paper · pdf · doi:10.48550/arxiv.2101.09546
36 pages, 15 figures
arxiv created 2021/01/23 · openalex publication_date 2021/01/23 · arxiv updated 2021/01/26 · openalex created_date 2022/07/25 · openalex updated_date 2026/07/28
A transient two-dimensional acoustic boundary element solver is coupled to a potential flow boundary element solver via Powell's acoustic analogy to determine the acoustic emission of isolated hydrofoils performing biologically-inspired motions. The flow-acoustic boundary element framework is validated against experimental and asymptotic solutions for the noise produced by canonical vortex-body interactions. The numerical framework then characterizes the noise production of an oscillating foil, which is a simple representation of a fish caudal fin. A rigid NACA 0012 hydrofoil is subjected to combined heaving and pitching motions for Strouhal numbers (0.03 < St < 1) based on peak-to-peak amplitudes and chord-based reduced frequencies (0.125 < f^* < 1) that span the parameter space of many swimming fish species. A dipolar acoustic directivity is found for all motions, frequencies, and amplitudes considered, and the peak noise level increases with both the reduced frequency and the Strouhal number. A combined heaving and pitching motion produces less noise than either a purely pitching or purely heaving foil at a fixed reduced frequency and amplitude of motion. Correlations of the lift and power coefficients with the peak root-mean-square acoustic pressure levels are determined, which could be utilized to develop long-range, quiet swimmers.