Experimental and simulation study on the effects of thermal and wind pressure on the aerodynamic performance of unpowered ventilation caps

As a critical component in building structures, unpowered ventilation caps effectively promote natural ventilation processes and reduce energy consumption. Thermal pressure and wind pressure are the main driving forces for its operation; however, related research is insufficient. This study investigates the effects of thermal and wind pressure on the aerodynamic performance of unpowered ventilation caps through experiments and numerical simulations. The analysis of the flow field within the ventilation caps and vertical shaft reveals that a pressure difference of 0–15 Pa between the inside and outside enhances the ventilation efficiency of the unpowered ventilation cap. As the pressure difference increases, the air exchange between the inside and outside of the ventilation caps accelerates, resulting in an increased ventilation volume. However, when the pressure difference exceeds 15 Pa, vortices form inside the vertical shaft or the ventilation cap. The dissipation of turbulent kinetic energy reduces the pressure difference in the ventilation cap, and additional aerodynamic drag becomes detrimental to ventilation and smoke exhaust. In addition, the P-Q curve of unpowered ventilation caps is established. This study provides a theoretical basis for optimizing the design of unpowered ventilation caps and supports the advancement of building energy-saving technologies.