Large-eddy simulation of stratification effects on dispersion in urban environments

Download

PDF - Post print Restricted to Admin only Download (2397Kb) | Request a copy

Description/Abstract

This paper focuses on investigating thermal buoyancy effects on dispersion of approach flows and local heat transfer from/to buildings by taking the DAPPLE site as the test case but for varying wind direction and magnitude. Firstly, based on the BT tower data, only weakly unstable conditions (i.e. Richardson number |Ri|<1) of approach flows were considered, with adiabatic boundary conditions at the ground and building surfaces. It was found that the predicted concentration in the far field was significantly reduced. Secondly, numerical experiments were performed, i.e. using various Richardson numbers. It was found that the modelled mean concentration for bulk Richardson number −0.9 was in reasonable agreement with field data at all stations. Thirdly, to understand the effects of weakly local unstable conditions, non-adiabatic boundary conditions at ground and building surfaces were implemented as well as weakly unstable conditions in the approach flows. No significant difference was found comparing with those using adiabatic boundary conditions. These simulations suggest that stratification effects on dispersion in weakly unstable conditions (e.g. in London) are not negligible.