Numerical analysis of the performance of a venturi-shaped roof for natural ventilation : influence of building width

A numerical analysis with Computational Fluid Dynamics (CFD) is performed to investigate the influence of building width on the performance of a venturi-shaped roof (called Ventec roof) for natural ventilation. The specific roof configuration is intended to create an underpressure in the narrowest roof section (contraction) which can be used to partly or completely drive the natural ventilation of the building zones. In previous studies, the influence of the roof configuration on its performance was analysed in detail, however these studies were all performed for a fixed building geometry, i.e. a tower building with floor plan 20×20 m² and a height of 50 m. It is important to analyse the performance of the Ventec roof for different building widths. Therefore, the present paper presents CFD simulations for building (and roof) widths of 20, 40, 80, 120 and 160 m. The 3D steady Reynolds-averaged Navier–Stokes (RANS) approach with the Renormalization Group (RNG) k–e model is used. The simulations are based on grid-sensitivity analysis and on validation by comparison with wind tunnel experiments. The simulations show that the aerodynamic performance of the roof in terms of the underpressure in the contraction improves with 31% when the building width is increased from 20 m to 40 m, while further increasing the building width only provides relatively small additional improvements. The increased performance with increasing building width is attributed to the larger overpressure upstream of the building and to the larger underpressure and larger size (height) of the wake behind the building.