Finite-element modeling of vocal fold self-oscillations in interaction with vocal tract: Comparison of incompressible and compressible flow model

Finite-element modeling of self-sustained vocal fold oscillations during voice production has mostly considered the air as incompressible, due to numerical complexity. This study overcomes this limitation and studies the influence of air compressibility on phonatory pressures, flow and vocal fold vibratory characteristics. A two-dimensional finite-element model is used, which incorporates layered vocal fold structure, vocal fold collisions, large deformations of the vocal fold tissue, morphing the fluid mesh according to the vocal fold motion by the arbitrary Lagrangian-Eulerian approach and vocal tract model of Czech vowel [i:] based on data from magnetic resonance images. Unsteady viscous compressible or incompressible airflow is described by the Navier-Stokes equations. An explicit coupling scheme with separated solvers for structure and fluid domain was used for modeling the fluid-structure-acoustic interaction. Results of the simulations show clear differences in the glottal flow and vocal fold vibration waveforms between the incompressible and compressible fluid flow. These results provide the evidence on the existence of the coupling between the vocal tract acoustics and the glottal flow (Level 1 interactions), as well as between the vocal tract acoustics and the vocal fold vibrations (Level 2 interactions).