Multiscale Build-up Area Integration in Parallel SWIFT

Parallel SWIFT is used in the AIRCITY project to model the air quality at a few meters resolution over the whole Paris area. Hence, it is crucial to provide the capability to correctly handle the downscaling from meso scale modelling to local scale modelling over build-up areas. Build-up areas have directional specificities due to the orientation of streets, or also the river Seine for the Paris case, that lead to directional bulk effects. To overcome this, we have developed an approach based on directional drag coefficients. Drag coefficients of buildings within their neighbourhood are derived once and for all for a set of wind directions. A methodology has been implemented in Micro-SWIFT to derive this, but data obtained from other CFD models can be used. This static database of drag coefficients is then used to create directional matrices of Cionco type canopy densities, at the wished resolution. The capability to handle and create canopy laws according to the flow direction has been implemented in SWIFT. Results are presented on test cases.