The University of Southampton
Arrays of buildings with pitched roofs are common in urban and suburban areas of European cities. Large eddy simulations were performed to predict the boundary-layer flows over flat and pitched-roof cuboids to gain a greater understanding of the impact of pitched roofs on urban boundary layers. The simulation methodology was validated for an array of flat roof cuboids. Further simulations showed that changes in the type of grid conformity had a negligible effect on the mean flow field and turbulent stresses, while having a visible, but small, effect on the dispersive stresses for a given packing density. Comparisons were made for flat and 45-degree pitched roof cuboid arrays at packing densities of 16.7% and 33.3%.
It was concluded that the interactions between pitched-roof buildings and their effect on the urban boundary layer were considerably different to those of flat-roof buildings. The pitched roofs at packing density 33.3% led to significant changes in the mean flow field, the Reynolds stresses, and the aerodynamic drag. Further work investigated the effects of changes in turbulence level and atmospheric thermal stratification in the approaching flow. Importantly, it was found that in comparison to a flat-roof array, the pitched-roof one at a packing density 33.3% evidently increased the friction velocity and greatly reduced the effects of stable stratification conditions and changes in inflow turbulence level.