DNS–URANS comparison study on cough-induced flow and particles in a large-scale circulation

Purpose The purpose of this study is to perform direct numerical simulation (DNS) and unsteady Reynolds-averaged Navier–Stokes simulation (URANS) of cough-induced flow and particles in a large-scale circulation (LSC) to assess the performance and accuracy of the latter. Design/methodology/approach Both simulations were performed in a 12.5 m³ room for 30 s, with a background flow defined by a lid-driven LSC. In the URANS, the particles were modelled using a stochastic dispersion model to account for turbulent fluctuations. Initial flow fields were obtained from LSC simulations. Findings The URANS predicted a larger cough jet entrainment, resulting in a shorter but wider jet flow, leading to underprediction of the horizontal displacements, especially of the small particles, during the jet and early puff phases. The cough puff in the URANS was overly influenced by the downward background flow, resulting in faster particle descent. The wider jet spread led to an overprediction of particle dispersion during the jet and early puff phases, but subsequently the shorter puff spread led to an underprediction of particle dispersion during the mid and late puff phases. Originality/value Unlike similar studies, this research includes DNS of a cough-induced flow and particles in a larger domain over a longer period of time within a background flow characterised by an LSC, highlighting the need for a better representation of the flow fields and cough-induced particle dynamics resolved in URANS.