Influence of flow separation location on phonation onset.

The influence of flow separation location on eigenmode synchronization and phonation onset was investigated in a two-dimensional, aeroelastic, continuum model of phonation. A linear stability analysis showed that flow separation played a critical role in initiating eigenmode synchronization and phonation. For a given glottal configuration, a small variation in the flow separation location along the vocal fold surface may lead to a qualitatively different eigenmode-synchronization pattern, and different phonation threshold pressure and frequency. This high sensitivity suggests a need for phonation models to be capable of accurate prediction of the flow separation location. Analysis with different glottal channel geometries showed that a minimum phonation threshold pressure existed for a rectangular glottal channel, consistent with previous experiments. However, in contrast to previous theoretical analyses, this study showed that phonation was facilitated, rather than prohibited, by the upstream movement of the flow separation point within a divergent glottis.