Frequency dependence of glottal jet dynamics with full and incomplete closure

This study focuses on frequency dependence effects on glottal jet dynamics with focus on the physiological condition where the vocal folds do not fully close. Incomplete closure occurs naturally, particularly in children and adult females. But there are also 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 stepper motor driven with constant opening and closing speeds inside a square duct. Cases with complete vocal fold closure and incomplete closure 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 and cycle-to-cycle analysis of key contributors to sound production was conducted. Acoustically relevant parameters, e.g., fluctuations in volume flow rate and transglottal pressure, are attenuated when vocal folds do not close completely. The key findings of this study, however, lie in statistical and dimensional scaling analysis of frequency dependencies of terms in the streamwise integral momentum equation. Specifically, the unsteady inertial term appears to become increasingly significant with increasing frequency and may be a key differentiator between lower frequency phonation, i.e. male voices, and the higher frequencies of children and adult females. These frequency effects, however, do not appear to be relevant to pathological conditions characterized by incomplete vocal fold closure.