Intraglottal pressure profiles for a symmetric and oblique glottis with a divergence angle of 10 degrees

Abstract

Human phonation does not always involve symmetric motions of the two vocal folds. Asymmetric motions can create slanted or oblique glottal angles. This study reports intraglottal pressure profiles for a Plexiglas model of the larynx with a glottis having a 10-degree divergence angle and either a symmetric orientation or an oblique angle of 15 degrees. For the oblique glottis, one side was divergent and the other convergent. The vocal fold surfaces had 14 pressure taps. The minimal glottal diameter was held constant at 0.04 cm. Results indicated that for either the symmetric or oblique case, the pressure profiles were different on the two sides of the glottis except for the symmetric geometry for a transglottal pressure of 3 cm H2O. For the symmetric case, flow separation created lower pressures on the side where the flow stayed attached to the wall, and the largest pressure differences between the two sides of the channel were 5%-6% of the transglottal pressure. For the oblique case, pressures were lower on the divergent glottal side near the glottal entry and exit, and the cross-channel pressures at the glottis entrance differed by 27% of the transglottal pressure. The empirical pressure distributions were supported by computational results. The observed aerodynamic asymmetries could be a factor contributing to normal jitter values and differences in vocal fold phasing.

Effect of channel asymmetry on the behavior of flow passing through the glottis

“…Besides the boundary-layer approximation, the glottal flow is thought to be quasi-steady and incompressible, since the typical Strouhal number is of the order of 10 À2 and the flow velocity is sufficiently lower than the sound velocity with a Mach number less than 0.1 [9]. Our previous study [11] also indicates that the one-dimensional IBL analysis is accurate for a symmetrical glottal channel; however, for an asymmetrical channel, the flow velocities of the left and right walls can differ [13,14,19], indicating that the analysis of the boundary-layer and core flow should, at least, be performed in two dimensions.…”

“…Vocal tract The vocal fold shape is represented using the model proposed by Scherer et al [13]. The model is mainly controlled by three parameters representing the minimum height of the channel (d) and the glottal angles ( L and R ).…”

On the viscous-inviscid interaction of the flow passing through the glottis

“…These earlier studies relied on a strong assumption that the flow always separates at the exit of the glottis. Later, flow measurement experiments [11,13] and computer simulations [5][6][7]14] proved that this assumption is not true. Magaribuchi et al [8] directly compared the flow behaviors when the separation point was estimated using the technique of boundary-layer analysis [9] with those when the separation point was fixed at the glottal exit.…”

“…4(B). When the glottal angle is greater than zero, the channel forms a divergent configuration and the minimum pressure is found just downstream of the glottal entrance [7,11]. Table 2 shows that the volume flow rate and the Reynolds number increases significantly when the channel height is increased, since they are nearly proportional to the sectional area of the channel at the separation point when the influence of the boundary layer is not considered [8].…”

“…To determine the configuration of the glottal channel, the shape of the vocal fold is represented using the model proposed by Scherer et al [11]. The model is controlled by parameters representing the minimum glottal The value of Áx in the numerical calculation of the boundary-layer problem in 2.3 is set to 10 À3 .…”