Finite element analysis of airflow in the vocal tract with lateral channels

Abstract

Lateral channels are airflow paths around the tongue produced by the laterally inward movement of the tongue toward the midsagittal plane during American English /l/ sound production. If contact is made with the palate, a closure is formed in the flow path along the midsagittal line. The closure is normally formed in the anterior part of the oral cavity and is about 1–1.5 cm long. However, it is speculated that the flow may split at a location posterior to the closure, thereby giving a longer length of the lateral channels up to 3–4 cm. Lateral channels of length around 3 cm have been shown to have significant effects on the resulting sound spectrum. To investigate the flow and acoustic field involved, finite element analysis was performed on a simplified model of the vocal tract during lateral sound production. The tongue was modeled as a rectangular constriction with a tapering slope on the upstream side and two flow channels on its two sides. The results show that the rising up of the tongue causes the flow to split into three regions of different flow amplitude and phase: one main region above the tongue surface and two regions around the tongue. This flow splitting occurs at the point where the tongue first begins rising up, well before the actual constriction location. The effective length of the lateral channels is therefore much longer than the length of the lingual constriction.