Available online xxxxIn recent years, the interest in double skin facades has increased because of esthetic reasons and for its use as passive system to save energy. Some authors have investigated their behavior related to thermal performance and energy efficiency compared to single skin facades but only considering the air cavity. The aim of this work is to identify a more efficient double glazed facade configuration that improves energy efficiency and indoor comfort conditions in buildings studying natural ventilation due to buoyancy-driven flow and heat transfer including solar radiation compared to a single skin facade. A simplified model was simulated using a computational fluid dynamics software to investigate the effects due to different cavity widths in winter and summer conditions with opened and closed vents and considering solar radiation or not. The main results obtained were that in winter closed vents is always efficient and ventilating is never beneficial. In summer closed vents is efficient in the absence of solar radiation and in its presence opened vents is favorable. Results showed the optimum air cavity width, and it was concluded that these double skin facades reduce the heating and cooling demands of a building, being more efficient compared to single skin facades.
This article deals with the effect of leading edge imperfections on the aerodynamic characteristics of a NACA 63 2 -215 laminar aerofoil at low Reynolds numbers. Wind tunnel tests have been performed at different Reynolds numbers and angles of attack and global aerodynamic loads were measured. To perform these tests, a NACA 63 2 -215 aerofoil was built up in two halves (corresponding to the upper side and to the lower side), the leading edge imperfection here considered being a slight displacement of half aerofoil with respect to the other. From experimental results, a quantitative measure of the influence of the leading edge displacement on the degradation of the aerofoil aerodynamic performances has been obtained. This allows the establishment of a criterion for an acceptance limit for this kind of imperfection.
A method to design a diffuser augmented wind turbine (DAWT) is proposed, using as a guiding point the optimal pressure drop at the turbine. The use of concepts and expressions derived from a ID analytic model helped to reduce the number of computational fluid dynamics simulations needed to find the optimal configuration. The proposed configuration can extract energy from the flow with the same efficiency as the state-of-the-art shrouded wind turbine (SWT) configurations but generating a significantly smaller wake, which makes this configuration a good candidate for wind farms or tidal applications. Furthermore, as a product of the ID model, universal curves for the power coefficient have been obtained, as a function of the thrust coefficient, or disk loading, which have been compared with numerical and experimental results, showing a good agreement. Finally, the maximum ideal power coefficient has been found for a given configuration, which helps to estimate the margin for improvement of an actual design.
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