Large-scale volumetric flow studies on transport of aerosol particles using a breathing human model with and without face protections

Abstract

Exhalation of small aerosol particle droplets and their airborne transport, dispersion and (local) accumulation in closed rooms have been identified as the main pathways for direct and indirect respiratory virus transmission from person to person, e.g. for SARS-CoV-2 or measles (Morawska and Cao 2020) (Chen et al. 2021). Therefore, understanding airborne transport mechanisms of aerosol particles inside closed populated rooms is an important key factor for assessing and optimizing various mitigation strategies (Morawska et al. 2020) (Morawska et al. 2013). Unsteady flow features, which are typically evolving in such mixed convection flow scenarios, govern the respective particle transport properties. Experimental and numerical methods are required which enable capturing the related broad range of scales in such internal flows over many cubic meters in order to provide reliable data for the adaptation of proper mitigation measures (distances, masks, shields, air purifiers, ventilation systems etc.). In the present work we show results of a large-scale 3D Lagrangian Particle Tracking (LPT) experiment which has been performed in a 12 m³ generic test room capturing up to 3 million long lived and nearly neutrally buoyant helium-filled soap bubbles (HFSB) with a mean diameter of dHFSB~ 370 µm as (almost) passive tracers. HFSB are used as fluid mechanical replacements for small aerosol particles dP < 5µm and allow to resolve the Lagrangian transport properties and related unsteady flow field inside the whole room around a cyclically breathing thermal manikin (Lange et al. 2012) with and without mouth-nose-masks and shields applied. Six high-resolution CMOS streaming cameras, a large array of powerful pulsed LEDs and the variable-time-step Shake-The-Box (VT-STB) (Schanz et al. 2016, Schanz et al. 2021) LPT algorithm have been applied in this experimental study of internal flows in order to gain insight into the complex transient and turbulent aerosol particle transport and dispersion processes around a seated and breathing human model.