Aeroacoustic Sound Source Characterization of the Human Voice Production-Perturbed Convective Wave Equation

Abstract

The flow-induced sound sources of human voice production are investigated based on a validated voice model. This analysis is performed using a hybrid aeroacoustic workflow based on the perturbed convective wave equation. In the first step, the validated 3D incompressible turbulent flow simulation is computed by the finite volume method using STARCCM+. In a second step, the aeroacoustic sources are evaluated and studied in detail. The formulation of the sound sources is compared to the simplification (neglecting the convective sources) systematically using time-domain and Fourier-space analysis. Additionally, the wave equation is solved with the finite element solver openCFS to obtain the 3D sound field in the acoustic far-field. During the detailed effect analysis, the far-field sound spectra are compared quantitatively, and the flow-induced sound sources are visualized within the larynx. In this contribution, it is shown that the convective part of the sources dominates locally near the vocal folds (VFs) while the local time derivative of the incompressible pressure is distributed in the whole supra-glottal area. Although the maximum amplitude of the time derivative is lower, the integral contribution dominates the sound spectrum. As a by-product of the detailed perturbed convective wave equation source study, we show that the convective source term can be neglected since it only reduces the validation error by 0.6%. Neglecting the convective part reduces the algorithmic complexity of the aeroacoustic source computation of the perturbed convective wave equation and the stored flow data. From the source visualization, we learned how the VF motion transforms into specific characteristics of the aeroacoustic sources. We found that if the VFs are fully closing, the aeroacoustic source terms yield the highest dynamical range. If the VFs are not fully closing, VFs motion does not provide as much source energy to the flow-induced sound sources as in the case of a healthy voice. As a consequence of not fully closing VFs, the cyclic pulsating velocity jet is not cut off entirely and therefore turbulent structures are permanently present inside the supraglottal region. These turbulent structures increase the broadband component of the voice signal, which supports research results of previous studies regarding glottis closure and insufficient voice production.

Aeroacoustic wave equation based on Pierce's operator applied to the sound generated by a mixing layer

“…Everything which remains in the source of AWE-PO are non-frozen source structures. Similar effects have been found in 3D for the perturbed convective wave equation and have not been explained yet [45,46].…”

Machine-learning applied to classify flow-induced sound parameters from simulated human voice

“…In previous works, a validated hybrid aeroacoustic model of human phonation has been established [2,25,26,27], which is called simVoice. To reduce the computational cost of a fluid-structure-acoustic interaction model [27], a prescribed vocal fold motion model is used [28].…”

Efficient numerical simulation of the human voice

“…The detailed description of the model with focus on the numerical efficiency is provided in [37], whereas a thorough description of the CFD incompressible flow simulation can be found in [31] and [30]. Furthermore, an extensive source term analysis for a validated synthetic setup is provided in [36] and the application to typical vocal cord dysfunctions is presented in [7].…”