Pedestrian wind comfort

Website Bert Blocken, PhD - Unit Building Physics and Services - Department of the Built Environment
Eindhoven University of Technology, The Netherlands

The construction of a building inevitably changes the microclimate in its vicinity. Wind speed, wind direction, air pollution, driving rain, radiation and daylight are all examples of physical aspects that constitute the outdoor climate and that are changed by the presence of the building. The change of these quantities depends on the shape, size and orientation of the building and on the interaction of the building with the surrounding buildings and other obstacles such as trees etc. These changes can be either favourable or unfavourable. Unfavourable changes include increased wind speeds around the building leading to uncomfortable or even dangerous conditions for pedestrians. This is particularly the case at the base of high-rise buildings. For example, Wise (1970) reports about shops that are left untenanted because of the windy environment which discouraged shoppers. Lawson and Penwarden (1975) report the death of two old ladies due to an unfortunate fall caused by high wind speed at the base of a tall building. Today, many urban authorities only grant a building permit for a new high-rise building after a wind comfort study has indicated that the consequences for the pedestrian wind environment remain limited. Wind comfort studies consists of combining statistical meteorological data, aerodynamic information and a comfort criterion. The aerodynamic information is partly supplied by physical simulation of the wind flow around the building configuration in a wind tunnel or by numerical simulation with Computational Fluid Dynamics (CFD). Some examples of wind comfort studies performed with CFD are shown in the figures below.

Research efforts on pedestrian wind conditions and wind comfort around buildings included the following aspects:

- Literature review on pedestrian wind comfort around buildings (Blocken and Carmeliet 2004) (preprint:

)

- Wind comfort assessment study for the Silvertop Towers in Antwerp, Belgium, and design of an automatic control system (Blocken et al. 2004) (preprint:

) (doi:10.1016/j.jweia.2004.04.004

- Wind comfort assessment study for residential building Joan Miro in Genk, Belgium (Blocken and Carmeliet 2008) (preprint:

)

- Wind tunnel study of the pedestrian wind conditions in the passage between two long narrow perpendicular buildings - discussion of wind-blocking effect and Venturi-effect in the passages (Blocken et al. 2008a) (preprint:

) http://dx.doi.org/10.1061/(ASCE)0893-1321(2008)21:4(280)

[From: Blocken B, Roels S, Carmeliet J. 2004. Modification of pedestrian wind comfort in the Silvertop Tower passages by an automatic control system. Journal of Wind Engineering and Industrial Aerodynamics 92(10): 849-873. (preprint:

) (doi:10.1016/j.jweia.2004.04.004)]

Silvertop towers by night. Three high-rise towers (L x B x H = 60 x 20 x 60 m³) that were subjected to a comprehensive restauration, part of which included adding passages through the building at ground level. Through-passages are typical problem spots for pedestrian wind nuisance, requested a wind comfort assessment study and - in this case - an automatic wind comfort control system.

Geometrical model and computational grid at the facade of tower 3 (Figure from

Amplification factors at pedestrian height (1.75 m) in the passages and around the towers. The amplification factor is defined as the ratio of the local wind speed to the wind speed that would occur at the same position without the buildings present. Very high amplification factors are found in the passages, up to 3 in the passage of tower 1.