Systematic influence of different building spacing, height and layout on mean wind and turbulent characteristics within and over urban building arrays

Large eddy simulations have been performed within and over different types of urban building arrays. This paper adopted three dimensionless parameters, building frontal area density (lambda(f)), the variation degree of building height (sigma(h)), and the staggered degree of building range (r(s)), to study the systematic influence of building spacing, height and layout on wind and turbulent characteristics. The following results have been achieved: (1) As lambda(f) decrease from 0.25 to 0.18, the mean flow patterns transfer from skimming flow to wake interference flow, and as lambda(f) decrease from 0.06 to 0.04, the mean flow patterns transfer from wake interference flow to isolated roughness flow. With increasing sigma(h), wind velocity within arrays increases, and the vortexes in front of low buildings would break, even disappear, whereas the vortexes in front of tall buildings would strengthen and expand. Tall buildings have greater disturbance on wind than low buildings do. (2) All the wind velocity profiles and the upstream profile converge at the height of 2.5H approximately. The decay of wind velocity within the building canopy was in positive correlation with lambda(f) and r(s). If the height of building arrays is variable, Macdonald's wind velocity model should be modified through introducing sigma(h), because wind velocity decreases at the upper layers of the canopy and increases at the lower layers of the canopy. (3) The maximum of turbulence kinetic energy (TKE) always locates at 1.2 times as high as the buildings. TKE within the canopy decreases with increasing lambda(f) and r(s), but the maximum of TKE are very close though sigma(h) varies. (4) Wind velocity profile follows the logarithmic law approximately above the building canopy. The Zero-plane displacement z(d) heighten with increasing lambda(f), whereas the maximum of and Roughness length z(0) occurs when lambda(f) is about 0.14. z(d) and z(0) heighten linearly with sigma(h) and r(s), If sigma(h) is large enough, zd may become higher than the average height of buildings.