2023_programme: Hydrofoil sound-source origin investigation by setting the Dynamic Mode Decomposition of PIV data into Lighthill's equation

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  • Session: 23. Ambient Noise Sources
    Organiser(s): -
  • Lecture: Hydrofoil sound-source origin investigation by setting the Dynamic Mode Decomposition of PIV data into Lighthill's equation
    Paper ID: 1891
    Author(s): Pinson Samuel, François Paul, Astolfi Jacques-André
    Presenter: Pinson Samuel
    Abstract: As it can affect performances, prone structural failures, disturb users, impact acoustic discretion and the whole ecosystem around, vibrations and noise of hydrodynamic lifting surfaces is a matter of great concern. Mention of discrete frequency tones from a sharp-trailing-edge airfoil at moderate Reynolds number appears in the early 70's. The phenomenon has been reconsidered very recently for aerodynamic applications and was found to originate from boundary layer velocity fluctuations at the trailing edge due to Tollmien-Schlichting waves. A recent work in the hydrodynamic tunnel of the French Naval Academy research center (IRENav) made it possible to study the flow around an hydrofoil when tonal noise emission occurs thanks to Time-Resolved Particle Image Velocimetry (TR-PIV) and laser vibrometry measurements at transitional Reynlods numbers. A Dynamic Mode Decomposition (DMD) was then used in order to extract the flow characteristics which correspond to organized vortex shedding of the wake at the tonal noise frequency. These structures show a strong coupling of the vortex shedding with the hydrofoil modal vibrations which raises the question on the origin of the emitted sound. To study the vortex-shedding sound-source hypothesis, DMD results are used as source terms in Lighthill's equation. Lighthill's tensor components are a product of velocity derivatives and thus are non-linear. Using the three modes (at 0 Hz, 197 Hz and 767 Hz) obtained by the DMD, Lighthill's tensor can be decomposed into a finite number of harmonic terms with frequencies being the combinations (sums and differences) of the three mode frequencies. Computation of the sound level from radiating components in the wavenumber domain show that the vortex shedding is not directly the origin of the perceived sound.
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  • Corresponding author: Dr Samuel Pinson
    Affiliation: IRENav EA 3634
    Country: France
    e-mail:

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