Quantification of the Intraglottal Pressure Induced by Flow Separation Vortices Using Large Eddy Simulation

Abstract

The greatest rate of change in the glottal flow rate during phonation is a rapid decrease that occurs during the latter part of the glottal closing. Previous works showed that intraglottal flow separation vortices (FSVs) form in a divergent glottis, produce negative gauge pressures (below atmospheric) during closing. It is hypothesized here that FSVs contribute to the rapid closing mechanism of the true vocal folds during phonation.Four idealized static models (M5) of the human larynx were investigated using large eddy simulation (LES): 2 models featured parallel folds that did not enable flow separation in the glottis and 2 models involved a divergent glottis. The influence of the ventricular gap (narrow/wide) is evaluated. An unsteady pressure inlet representing a voicing cycle was applied to the sub-glottal region to mimic the time-varying glottal flow.Intraglottal vortex structures formed downstream of the separation point in a divergent glottis. Their existence caused a higher closing force that was applied onto the vocal folds. A narrow ventricular gap strengthens this effect.Strength of the intraglottal vortices increased with the maximum flow declination rate. Therefore, a more divergent shape of the glottis during glottal closing will be one of the main contributors to the voice quality.

Overview on state-of-the-art numerical modeling of the phonation process

“…Regarding the vocal fold shape, most studies used the so-called "M5 model geometry" shown in Figure 2 which was first introduced as experimental static model by Scherer et al [13]. Although not officially defined as benchmark model, the M5 model became widely accepted for experimental and computational studies including static [14][15][16][17][18][19][20] as well as vibrating vocal folds of all types, i.e. driven dynamics [21][22][23][24][25][26][27][28][29][30].…”

“…Thus, several computational studies investigated the flow through static vocal folds at different instances during the oscillation cycle represented by different convergent or divergent transglottal shapes of the coronal glottal duct [14-17, 19, 20]. Most of these models are quasi-2D with a uniform rectangular glottis and without ventricular folds and vocal tract except the model by de Luzan et al [20] who performed simulations with 3D M5 models with uniform or divergent glottal duct. Beside the M5 model, other customized and/or physiologically based model types [11,31] as well as those with a much simpler geometry of the vocal folds as e.g.…”

“…Besides the geometry of the immediate glottal region with the two vocal folds, the upstream and especially downstream regions of the computational models are essential parts to study the laryngeal aerodynamics. Especially the ventricular folds immediately downstream of the vocal folds have been of special interest in computational studies [20,27,33]. In contrast to the vocal fold geometry, the shape of the ventricular folds is less standardized sometimes with half-circular shape [32,33], some circular with divergent expansion [23,24] and some transferred from the M5 model geometry [25,27,28].…”

“…In contrast to the vocal fold geometry, the shape of the ventricular folds is less standardized sometimes with half-circular shape [32,33], some circular with divergent expansion [23,24] and some transferred from the M5 model geometry [25,27,28]. The important geometric parameters in this context and thus focus of the related studies [11,20,32,33] are the length of the ventricles being the space between vocal and ventricular folds and the gap between the ventricular folds. Also the pure aerodynamic influence of the ventricular folds were in the focus of computational studies [24,27].…”

The Effects of Negative Pressure Induced by Flow Separation Vortices on Vocal Fold Dynamics during Voice Production

“…Later experimental and computational studies also showed that the strength of FSV, and subsequently the negative pressure they augment, are proportional to the magnitude of the glottal divergent angle [3,8]. Farbos de Luzan et al [18] quantified the intraglottal negative pressure induced by FSV using large eddy simulation by comparing the pressure fields between a divergent channel and a straight channel. The geometric model is static but with a time-varying pressure waveform applied at the inlet of the domain.…”