The Coanda effect and asymmetries in vocal fold models during phonation

National audienceThe possibility of having an asymmetrical flow through the glottis (Coanda effect) is often reported in the literature as an overlooked feature which could have important effects. Assuming a certain geometry of divergent vocal folds, we show how Thwaites boundary layer theory gives an analytical result for the separation point of a subglottal jet through the glottis. This allows us to predict the width of the glottal jet when it separates from the wall as occurs in the Coanda effect. The result is in agreement with previous empirical observations of glottal jet separation width. To test the impact of the Coanda effect on vocal fold oscillations predicted by means of two mass vocal fold models, we show results of simulations with and without the asymmetric lateral pressure force induced by the Coanda effect. We study the effect with symmetrical and asymmetrical mechanical properties of the two vocal folds. We find that there is a minor effect of flow asymmetry on the result for the symmetrical vocal folds, while the effect is more complex in the asymmetrical fold case. We suggest paths for future research involving the flow separation effects on vocal fold oscillation