Experimental and numerical analysis of a wind roof design for natural ventilation

An experimental and numerical analysis of the flow conditions in a venturi-shaped roof has been conducted, focusing on the negative pressure in the narrowest roof section (contraction). Natural ventilation of the building zones can be driven by this negative pressure, either completely or partly. The wind tunnel experiments are performed in an atmospheric boundary layer wind tunnel at scale 1:100. The 3D CFD simulations are performed with steady RANS and the RNG k-e model. The aim of this study is to assess the magnitude of the negative pressures generated with different design configurations of the venturi-shaped roof, i.e. the presence and number of guiding vanes. The CFD simulations have been validated using the wind tunnel experiments of mean wind speed and surface pressures inside the roof. The simulated results are generally within 10% of the wind tunnel measurements, indicating a very close agreement. The study shows that the largest negative pressure coefficients are obtained for the configuration without guiding vanes, down to -1.35, with reference to the free-stream wind speed at roof height. At first sight, a counter-intuitive result is visible when comparing the design configurations with and without guiding vanes: adding guiding vanes strongly decreases the absolute value of the negative pressure. The wind tunnel measurements and the CFD simulations showed that the optimum configuration is the one without guiding vanes. An explanation can be found in the presence of the guiding vanes which increase the flow resistance inside the roof and cause more wind to flow over and around the roof, and less wind through it (wind-blocking).