CFD simulations on high-buoyancy gas dispersion in the wake of an isolated cubic building using steady RANS model and LES

Abstract

As the use of emergency generators for buildings increases, the near-field dispersion of high-temperature and high-buoyancy exhaust gas is becoming a concern. We conducted computational fluid dynamics (CFD) simulations using steady Reynolds-averaged Navier-Stokes (RANS) model and large eddy simulation (LES) on the near-field dispersion of high-buoyancy exhaust gas emitted from a building's wake and validated using a wind tunnel experiment. Realizable k-ε 2-layer and wall-adapting local eddy viscosity (WALE) models were used in RANS and LES, respectively. The density difference between the light gas and ambient air in the experiment was reproduced as the temperature difference by an incompressible ideal gas model. RANS model exhibited good agreement with the experimental flow field values for the time-averaged velocity but underestimated the turbulent kinetic energy. LES accurately predicted both the time-averaged velocity and turbulent kinetic energy. For the concentration field, RANS model predicted the region of high time-averaged concentration near the exhaust port but overestimated ground-level values. Meanwhile, LES adequately predicted time-averaged and fluctuating concentrations. Additionally, an investigation of the effect of the turbulent Schmidt number Sct in RANS model demonstrated that a small Sct increased the overall prediction accuracy, while a large Sct compensated for the overestimation on ground-level time-averaged concentrations.