Computational aeroacoustics of phonation, Part I: Computational methods and sound generation mechanisms

Abstract

The aerodynamic generation of sound during phonation was studied using direct numerical simulations of the airflow and the sound field in a rigid pipe with a modulated orifice. Forced oscillations with an imposed wall motion were considered, neglecting fluid-structure interactions. The compressible, two-dimensional, axisymmetric form of the Navier-Stokes equations were numerically integrated using highly accurate finite difference methods. A moving grid was used to model the effects of the moving walls. The geometry and flow conditions were selected to approximate the flow within an idealized human glottis and vocal tract during phonation. Direct simulations of the flow and farfield sound were performed for several wall motion programs, and flow conditions. An acoustic analogy based on the Ffowcs Williams-Hawkings equation was then used to decompose the acoustic source into its monopole, dipole, and quadrupole contributions for analysis. The predictions of the farfield acoustic pressure using the acoustic analogy were in excellent agreement with results from the direct numerical simulations. It was found that the dominant sound production mechanism was a dipole induced by the net force exerted by the surfaces of the glottis walls on the fluid along the direction of sound wave propagation. A monopole mechanism, specifically sound from the volume of fluid displaced by the wall motion, was found to be comparatively weak at the frequency considered (125 Hz). The orifice geometry was found to have only a weak influence on the amplitude of the radiated sound.

Computational modeling of phonatory dynamics in a tubular three-dimensional model of the human larynx

“…With the remarkable advances in computational power as well as computational modeling techniques in the last several decades, continuum based models of phonation have undergone rapid improvement. Initial attempts were mostly with two-dimensional (2D) models (Zhao et al, 2001;Zhao et al, 2002;Zhang et al, 2002;Alipour and Scherer 2004). Furthermore, immersed boundary method based solvers have also found an increased use in these models (Duncan et al, 2006;Luo et al, 2008;Luo et al, 2009;Zheng et al, 2009) due to their inherent ease of application to complex biological problems with moving/deforming boundaries.…”

Computational aeroacoustics of human phonation

“…In some cases, especially when the vocal folds are abducted (e.g. in breathy phonation), the acoustic consequence of the dipole sound sources due to unsteady forces exerted by the vocal folds on the fluid may also grow important [6]. The acoustic signal generated in the glottal region is further modulated by the vocal tract, radiated from the mouth, and perceived as voice.…”

“…These include studies with fixed vocal folds (e.g. [12,13,14,15]), forced vocal fold oscillation [16,17,6,18,19,20,21,22,23] and models with the airflow fully coupled to elastic tissue oscillations [24,25,26,27,28,29,30]. Only a few of these computational studies [24,12,14,15,22] solve the flow field in 3D, and most of them on a static geometry.…”

“…Gowan [5]. Zhao et al [6] computed the acoustic radiation by direct simulation, and compared the results with Ffowcs Williams-Hawkings analogy. In a study based on LES-based computational techniques, Suh & Frankel published acoustic-analogy-based far-field sound predictions and compared them to direct simulations.…”

A Unified Numerical Simulation of Vowel Production That Comprises Phonation and the Emitted Sound

“…The pressure at the glottis decreases due to the jet flow in the vocal tract (VT) by Bernoullis law and a self sustained oscillation is established. The flow dynamics and VF vibrations result in acoustic sources of monopolar, dipolar and quadrupolar character [3]. Acoustic waves are generated, propagate through the VT and become finally radiated outwards.…”