The formation of flow separation vortices inside the glottis during vocal fold closing

Abstract

Our previous work highly suggests that glottal airflow contains certain vortical structures, especially flow separation vortices (FSV) that significantly contribute to acoustics. We have previously identified these FSV directly above the folds but not between the folds. We have now developed a technique that allows us to see both intraglottal velocity fields and the medial wall of the folds during vocal fold closing. In this study, we used the new technique in an excised canine larynx to simultaneously measure intraglottal velocity fields (using high speed particle image velocimetry) and the medial surface of the folds. We observed the formation of FSV inside the glottis. Intraglottal pressures were calculated from measured intraglottal velocity fields using the Navier–Stokes equations. The maximum negative intraglottal pressure on the medial surface of one fold was −6 cm H2O. The circulation of the transglottal flow was highly correlated to the maximum closing speed (MCS) (r=0.98, p<0.001), and had good correlation to the spectral slope (r=-0.8, p<0.01) and HNR (Harmonic to Noise Ratio) (r=0.85, p<0.005). These results substantiate our hypothesis and our new technique is significant because it will allow us to experimentally characterize the intraglottal flow-structure relationship during vocal fold closing.