Jet dynamics in a scaled up vocal fold model with full and incomplete closure*

This study focuses on phonation in the physiological condition where the vocal folds do not fully close. While this occurs naturally in children and adult females, there are pathological conditions which can be problematic. Experiments were conducted using a 10x scaled-up model in a free surface water tunnel. 2-D vocal fold models with semi-circular medial surfaces were driven inside a square duct with constant opening and closing speeds. Cases where the vocal folds closed fully and to only 15% of the maximum gap were examined. Time resolved DPIV and pressure measurements along the duct centerline were made at Re = 7200 over equivalent life frequencies from 52.5 Hz to 97.5 Hz. Phase-averaged analysis of key contributors to sound production was conducted along with a dimensional scaling analysis to examine frequency dependencies between different terms in the streamwise integral momentum equation. When the folds do not fully close, there is always a non-zero mean flow downstream of the glottis which significantly alters the dynamics. Extrapolation to higher frequencies suggests changes in force distributions on vocal folds as unsteady inertia becomes of the same order as the transglottal pressure force. Implications on energetics and sound quality are explored.