The air we breathe when speaking: links between language and fluid mechanics*

Clear evidence shows that airflow jets produced when we speak contribute to the transport of airborne pathogens, such as the SARS-CoV-2 virus. In linguistics, there are clear distinctions in the manners of articulation and airstream mechanisms between vowels and consonants. However, it is still elusive how the linguistic features of vowels and consonants may determine the fluid mechanics features of the airflow jets that accompany speech. We combine experimental and numerical approaches to investigate the flow patterns produced by representative vowels—/a, i, o, u, ə/, and consonants—/p, k, f, s, h/. A 3D vocal tract is modeled with a temporally varying exit that captures key morphologic and kinematic features of the human vocal tract, including teeth and lips. An incompressible flow solver based on a sharp-interface immersed-boundary-method (IBM) is employed to compute the resultant airflow. By examining various combinations of vowels and consonants, we show that the combined effort of a large volumetric flow rate dominated by consonants and high flow speed determined by vowels contribute to faster and longer penetrations of airflow jets. We also show relative position between lips and teeth determines the orientation of the jets. This work helps bring insights into the understanding of articulatory phonetics, and the links to different languages, from a fluid mechanics perspective.