Principal aerodynamic mechanisms in phonatory flow

This article presents high-fidelity simulations of fully coupled interaction between a slightly compressible fluid and the compliant vocal folds through which it flows. The focus here is identification of the dominant aerodynamic mechanisms in phonation. The modified Immersed Finite Element Method is used to compute self-sustained vibration of three-layer, viscoelastic model vocal folds with a skewed elliptical shape. Simulations, performed for Reh= 2350 and reduced frequency f*= 0.11, and driven by a lung pressure of 1 kPa, were used to estimate terms of the integral mass conservation, momentum, and mechanical energy equations, as well the Bernoulli equation. The vocal folds vibrated at 227 Hz, with subharmonic modulation. Analysis of the surface motion showed three modes that captured 99% of the energy. Analysis using the integral equations shows that the aerodynamics is essentially described by a balance between pressure drag on the vocal folds and the pressure force pushing fluid through the vocal folds. Furthermore, it was shown that fluid dynamic friction is always negligible compared to the pressure forces. Flow work comprised the energetic input, and the primary output was the work on the vocal folds (21% of input), with losses comprising 70% of input. Analysis of the Bernoulli equation shows that the flow is inherently unsteady at the beginning and end of a vibration cycle, when the vocal folds are nearly closed, and that, in the jet flow region, the unsteady and convective accelerations nearly offset one another. These results are consistent with those from driven wall experiments.