Effects of Vertical Glottal Duct Length on Intraglottal Pressures in the Convergent Glottis

In a previous study, the vertical glottal duct length was examined for its influence on intraglottal pressures and other aerodynamic parameters in the uniform glottis [J Voice 32, 8–22 (2018)]. This study extends that work for convergent glottal angles, the shape of the glottis during the glottal opening phase of vocal fold vibration. The computational fluid dynamics code ANSYS Fluent 6.3 was used to obtain the pressure distributions and other aerodynamic parameters for laminar, incompressible, two-dimensional flow in a static vocal fold model. Four typical vertical glottal duct lengths (0.108, 0.308, 0.608, 0.908 cm) were selected for three minimal diameters (0.01, 0.04, 0.16 cm), three transglottal pressures (500, 1000, 1500 Pa), and three convergent glottal angles (−5°, −10°, −20°). The results suggest that a longer vertical glottal duct length increases the intraglottal pressures, decreases the glottal entrance loss coefficient, increases the transglottal pressure coefficient, causes a lower gradient of both the intraglottal flow velocity and the wall shear stress along the glottal wall—especially for low flows and small glottal minimal diameters—and has little effect on the exit pressure coefficient and volume flow. The vertical glottal duct length in the convergent glottis has important effects on phonation and should be well specified when building computational and physical models of the vocal folds.