Saliva particles transport during normal breathing through mouth and nose

We performed a direct numerical simulation to investigate the transport of saliva particles during human breathing through nose and mouth. The air-saliva mixture’s flow is resolved via Eulerian method that was coupled with a Lagrangian particle tracking method to obtain trajectories of saliva particles. Using the coupled approach, we acquire valuable insights into the intricate dynamics of Lagrangian coherent structures (LCS) and fundamental material lines that arise from the trajectories of saliva particles throughout various breathing cycles. Furthermore, we systematically compared the characteristics of LCSs between regular mouth breathing and the combined breathing through both the mouth and nose, using quantitative measures. The analysis of the simulation results revealed that shortly after the initial breathing cycle, saliva particles arrange themselves into a series of vortex rings that roll up and move forward. These advancing vortex rings contribute to the formation of an asymmetrical primary forefront vortex. The individual vortex rings consistently progress forward, merging with the forefront vortex, and ascend along the edge of the leading vortex.