Development of a computational fluid dynamics model adopting a nested grid system: Flow simulations for ideal and real urban settings

Abstract

We incorporate a nested grid system into a computational fluid dynamics (CFD) model based on the Reynolds-averaged Navier-Stokes equations. First, we evaluate the CFD model by comparing the results simulated in an array of aligned buildings using one- and two-way nested and non-nested coarse (same grid size as the parent domain) and fine grid (same grid size as the child domain) systems. The two-way nested grid simulates double-eddy circulation, wind speeds, and turbulence kinetic energy (TKE) in a street canyon better than the one-way nested grid. The nested simulations produce similar results to the fine grid system but with a significantly reduced CPU time. We also apply the nested grid system to airflow simulations in a building-congested district and validate the simulated results against the wind speed and direction measured by an automated weather system. The nested simulation improves wind direction compared to the WRF model operated by the National Institute of Environmental Research of South Korea. The two-way nested grid successfully reproduces the measured wind speed. The two-way nested grid simulation well represents the continuous flow structure (a smooth flow transition) between the parent and child domains by considering the two-way flow interaction between the two domains.