Roof slope effects on the aerodynamic characteristics of tall buildings

Roof shape of a building placed in a wind flow has particularly significant effects on this flow, in its wake, immediately at the vicinity and far from the structure. This influence is given by an experimental study, undertaken on rectangular models of reduced scale skyscrapers (1:1000), in a subsonic wind tunnel that enabled us to measure the exerted force by wind flow on windward face of the buildings, as well as the pressure distribution according to the longitudinal and the transverse building directions. The drag force acting on the models windward face is very affected by the building slope roof; these results are available for a normal and inclined wind direction. A numerical simulation is carried out to reproduce complex flow developed around the different building models, using Fluent software. We obtain the parietal pressure distribution on the various building faces and we compare the numerical values to the experimental data obtained in the wind tunnel, both are in good agreement with those provided by the international ASCE code. The numerical simulation indicates that complex structure vortices are developed at the buildings wake and allows us a better understanding of the flow phenomena. Analysis of the numerical results reveals a distinct evolution of pressure and velocity fields, the induced downstream flow is particularly complex. The presence of a roof deforms swirling zones: the zone of recirculation in buildings wake is stretched and the flow diagram is modified, which has direct effects on the measured wind force and the pressure distribution.