Macroscopic simulations of turbulent flows through high-rise building arrays using a porous turbulence model

Wind flowing through urban areas may help diluting pollutants in street networks. General microscopic numerical techniques have difficulty in simulating wind through city-scale urban areas with thousands of buildings because the required computational load is difficult to afford. We considered urban canopy layers with buildings and street networks as porous media and used a porous turbulence model to macroscopically study urban airflows. High-rise porous building arrays with uniform building heights or building height variations were studied (building height/street width, i.e. H/W = 2 or 2.67; the porosity or the fraction of air volume in urban areas is φ = 0.75). A single domain approach was used to account for the interface conditions. Microscopic simulations using RANS k-ɛ turbulence model and validated by wind tunnel data were also carried out to model the form drag produced by buildings and calculate spatially-averaged flow quantities to estimate macroscopic simulation results using the porous turbulence model. Results showed that, with a parallel approaching wind, the present porous turbulence model may predict macroscopic mean flows through porous building array generally well if suitable porous parameters are modelled, meanwhile, some microscopic flow information is lost but the computational requirements are effectively reduced. With a power-law approaching wind, a taller porous building array may experience greater macroscopic velocity if the length of porous region is effectively limited. Further investigations are still required to evaluate macroscopic turbulence predictions and apply present porous turbulence model for real urban areas or cities with various wind directions.