Study on the influence of voids on high-rise building on the wind environment

Li, Yangluxi; Chen, Lei

List of symbols C μ , C 1ε , C 2ε , σ k , σ ε constants in the standard k-ε model I turbulence intensity k turbulence kinetic energy l turbulence length scale L associated size P mean static pressure H D Re Reynolds number S i source item u i mean wind velocity at i direction u j mean wind velocity at j direction u G mean wind velocity at the gradient height u¢ turbulent fluctuating velocity i u¢ fluctuating velocity component at i direction u averaged fluid velocity ABL u * ABL friction velocity U r reference wind velocity v  modified turbulent viscosity x, y, z Cartesian co-ordinates z 0 roughness length(or height) z G gradient height δ ij Kronecker=1, delta for i = j, and =0 for i ≠j ε dissipation rate of k κ Von Kaman constant μ t turbulence viscosity ρ fluid density Stathopoulos and Wu 1995; To and Lam 1995; Kubota et al. 2008) . Many impact factors such as shape, space layout, orientation of buildings and street canyons were studied, and the results provide precious insights in view of the pedestrian-level wind environments around buildings (Stathopoulos et al. 1992; Visser et al. 2000) . Nevertheless, most of these studies only concentrated on small regions with high wind speed such as building corner nearby. For a group of buildings or row of constructions, some researches had been done primarily investigated the passage between constructions. The height and width of the building, the separation between the building and the podium ventilation effects were performed to be studied by the different architectural shapes consisting of single building, two buildings, a row of building and so on. Natural ventilation and pedestrian comfort were also assessed via experimental design and analysis (Chan et al. 2001 (Chan et al. , 2003 . Note that, beyond that there were a few studies to investigate the influences of modern building structures (such as buildings with platforms) on the relatively large area of low flow velocity at the leeward of the building. Blocken and Stathopoulos (2013) performed a comprehensive investigation in regard to CFD simulation on pedestrian-level wind condition utilizing a normalized mean wind speed (U/Ur) rather than speed ratio K because it could easily combine specific wind climates to determine wind speed statistics based on the magnitude and frequency of occurrence. This contributed to determine effectively the boundaries of low wind velocity region. For instance, the normalized mean wind speed (U/U r ) about 0.3 was needed so as to achieve a threshold wind velocity approximately 1.5 m/s that was the lowest wind velocity observable at the pedestrian level (Lawson and Penwarden 1975) . Therefore, U/U r lower than 0.3 was considered as the low wind velocity area which had negative influence on the ventilation. This pedestrian horizontal wind speed of 1.5 m/s threshold was consistent with Ng (2009) as the Hong Kong air circulation assessment criteria, taking into account the environment temperature and solar irradiance at that time. It can be seen from that definition of area utilizing wind climate in Hong Kong was a good method. The normalized mean wind velocity (U/Ur) distribution given here was known as a general result of the characteristics of airflow around the object building.