Excitation of Airborne Acoustic Surface Modes Driven by a Turbulent Flow

Abstract

This experiment demonstrates the generation of trapped acoustic surface waves excited by a turbulent flow source through the coupling of pressure fluctuations at the interface between an acoustic metamaterial and a flow environment. The turbulent flow, which behaves as a stochastic pressure source, was interfaced with an acoustic metasurface waveguide stationed in a quiescent environment via a single Kevlar-covered cavity, which ensured no significant disturbance to the flow. The metasurface waveguide produced an acoustic surface mode through evanescent diffractive coupling of the pressure field. This acoustic mode was trapped at the quiescent surface, with its mode dispersion determined by the surface geometry. The results of two different metasurface geometries are discussed: 1) a slotted cavity array, and 2) a meander connected cavity array, with each demonstrating a different trapped surface wave characteristic. Fourier transform and correlation analyses of spatially resolved temporal acoustic signals, measured close to the metamaterial surface, were used to construct the frequency-and wavevectordependent acoustic mode dispersion. The results demonstrate that the flow can be used to excite acoustic surface modes and that their mode dispersion may be tailored toward realizing novel control of turbulent flow through acoustic-flow interactions.

Vibroacoustic analysis of dental air turbine noise

“…Resonance phenomenon of an enclosed air by acoustic or vibrational excitation has been studied in various fields [ 33 – 37 ]. The excitation source can be turbulent air inflow or vibration transmitted through casing [ 38 – 40 ]. This study analyzed the resonance phenomenon of air layer inside the dental handpiece excited by the inflow of compressed air.…”

Directionally Sensitive Sensor Based on Acoustic Metamaterials

“…………………………………………………………………………………………………………...7 Figure 1.5: Photo of (A) the Virginia Tech Anechoic Wall-Jet Tunnel, (B) the microphone traverse set-up, and (C) the traversing microphones. (Damani, 2020) [11]. …………………………………………………8 Figure 1.6: (A) Underside views of both metasurfaces, (B) unit cell geometry for the meander metasurface, (C) unit cell geometry for the slotted metasurface, and (D) a schematic for the metasurface and traversing microphone set-up.…”

“……………………………………………………………………………………………9 Figure 1.7: Wavenumber-frequency spectra for (A) the slotted metasurface and (B) the meander metasurface. The blue circles represent the solution from the respective COMSOL simulations [11]. ……………………………………………………………………………………………………………....9 The frequency spectrum against streamwise microphone separation for the traverse microphones and the metasurface configure to (A) a single through-cavity and (B) 17 through-cavities.…”

“…These waves are evanescent, surface bound pressure waves that travel over a suitably structured surface decaying exponentially away from the surface they are bound to. The ASWs develop due to the diffractive coupling between the local pressure fields along the linear array of resonating cavities [9][10][11]. Damani (2020) describes such a metasurface which uses a single half-wave through-cavity to excite the quarter-wave metamaterial substructure.…”

“…The implications of this were that a metasurface could be excited using turbulent flow as a stochastic source and not be disturbed by the cavity array. The direct continuation of this work was carried out by Damani et al shortly after [11]. Although Repasky's thesis implied that a turbulent flow may be used as a stochastic pressure source to excite a metasurface over a broad range of frequencies, it was not experimentally proven until Damani et al Damani et al describes the fabrication and testing of two similar metasurfaces solely under flow excitation, whereas primarily acoustic excitation has been done previously [11].…”