Experimental and CFD analysis of particle distribution in a controlled test facility: Impact of exhalation flow velocity and direction

• Constant respiration conditions are often used in indoor particle dispersion studies • Limited study on how source conditions affect the indoor particle concentration • Interactions between indoor airflow patterns and source conditions are studied • Changes in source conditions mainly affect the local velocity distributions • Local concentration distribution is significantly affected by the source conditions The dispersion of exhaled particles in indoor environments is significantly influenced by the airflow conditions. Constant human respiration conditions are widely employed in experiments and CFD simulations for indoor particle transmission studies. However, it remains challenging to reach a definitive consensus on how the exhalation flow velocity/rate and direction interact with the indoor airflow pattern and influence the indoor particle distributions. The goal of this study is to systematically investigate the impact of constant source conditions, specifically the exhalation flow velocity (EFV) and direction (EFD) at the source, on the particle distribution in a controlled test facility by experiments and CFD simulations. First, the velocity, temperature and concentration results obtained from CFD simulations, employing the RNG k-ε turbulence model, are validated with experimental results. Next, the validated computational setup is used for CFD simulations of the same test facility, incorporating two mixing ventilation configurations. Under each ventilation configuration, three different EFV (i.e. 2.33, 4.65, and 9.30 m/s), each with three EFD (i.e. positive y, negative y , and positive x ), and a reference case with no EFV/EFD at the source are considered. The effect of the variation of EFV and EFD on the surface-averaged concentration ( C avg ) on the breathing height plane ( z = 1.2 m) generally remains below 5.8%, compared to the reference cases (no EFV/EFD). However, when considering the C avg over a central area near the source, the C avg deviation can reach up to 29.9%. This study enhances the understanding of indoor particle transmission and its dependency on the EFV and EFD.