Spatial averaged properties of turbulent flow over staggered arrays of cubes with different packing densities: Analysis of the sectional drag coefficients

The interaction between atmospheric flow and urban geometry (especially buildings) produces complex airflow patterns within the urban canopy. A detailed understanding of this interaction is very important from the point of view of urban canopy modeling. Recently, simplified urban canopy models have been developed using numerical approaches that do not resolve buildings, but that employ parameterizations of the drag and turbulence within the building canopy. Since the drag and turbulence clearly depend upon the building geometry, an important challenge is to develop parameterizations that are formulated explicitly in terms of the building geometry. CFD models that resolve every building can play an important role here. The detailed spatial data produced by CFD simulations of the turbulent flow around the buildings can be analyzed to compute spatial averages of flow variables over the grid cell volume of the urban canopy models. An important input parameter for the simplified urban canopy models is the effective sectional drag coefficient (CD(z)) of buildings in an array. Hence, the computation of CD(z) for a range of building packing densities and geometries is very useful for these models. In this work, the turbulent flow over staggered arrays of cubes with different packing densities is simulated using a CFD RANS model. Spatially averaged properties of the airflow within the urban canopy are deduced from the RANS results. Different sectional drag coefficients are computed and a first attempt to parameterize them for this type of configuration is made.