On the Variation of Fricative Airflow Dynamics with Vocal Tract Geometry and Speech Loudness

Recent studies have determined that the number of respiratory droplets expelled during a short duration of speech can be comparable to that of a cough. Although speaking is typically modeled as a horizontal jet, recent experimental work has shown that there are large angular variations when fricative sounds are produced. To investigate this, two-dimensional vocal tract geometries for a labiodental fricative, [f] and a dental fricative, [θ] were constructed based on magnetic resonance imaging (MRI) during these intonations. Two-dimensional ANSYS-Fluent simulations were performed to investigate the expiratory airflow from the geometries, which showed chaotic unsteady airflow trajectories with maximum velocities ranging from 20 to 40 m/s and jet trajectory angles varying between ±60°. The simulations highlight the variabilities of the expirated airflow trajectories as a function of the type of utterance, speech loudness, size of the mouth opening, and tongue shape.