Quantifying Time-Evolving Droplet Velocities and Size Distributions for CFD Validation: Insights from Experimental Image Analysis*

Respiratory droplets, spanning sizes from approximately 0.1 µm to 1,000 µm, are emitted during various expiratory activities. These fine particles, characterized as aerosolized respiratory particles, can travel substantial distances through air currents. Understanding these characteristics is crucial for assessing the risk of airborne transmission.

 

However, existing experimental studies often report time-averaged or spatially averaged results, overlooking the transient behavior of droplets. Additionally, measuring velocity profiles independently of droplet size profiles remains challenging due to the difficulty in tracking individual droplets. To address these gaps, we use a high-speed camera system to capture evolving velocity and droplet size distribution over time and space. By analyzing particle image velocimetry (PIV) and Particle Tracking Velocimetry (PTV) data, the temporal and spatial velocity profiles, droplet sizes, and droplet number distributions at various locations relative to the nozzle are quantified.

 

Furthermore, our research leverages PIV and PTV results from near and far fields as time-varying boundary conditions and validation datasets for computational fluid dynamics (CFD) simulations. It enhances the accuracy and reliability of these simulations in predicting droplets spreading properties. Our approach enables detailed, transient analysis of respiratory droplet dynamics, contributing to a better understanding of airborne transmission risks.