Study of wind effects on different buildings of pitched roofs

摘要

The characteristics of wind flow past simplified models of one-side pitched roof buildings were examined in a wind tunnel that was designed and built at the Housing and Building Research Center (HBRC).The wind tunnel consists of a square cross section of 200 mm x 200 mm (a bellmouth intake,main entrance duct,a flow straightener,a transition section,and a suction fan).The tunnel was calibrated by a pitot-static tube,determining the flow rate and mean velocity upstream of the models.Static pressure distributions on the external surfaces of models were measured with a free stream velocity of 7 m/s.Smoke visualization tests were also carried to obtain qualitatively the flow patterns around a simulated building models.The flow visualization results gave a good qualitative agreement with measurements.The separation zone,the reattachment length,and the wake region width were clear in the visualization-obtained patterns.The temperature distribution at various points over the pitched roof was measured and the heat transfer coefficient was normalized by the heat transfer coefficient for a 0°.pitch roof.A CFD computer package (ANSYS) based on the finite element method was used to predict velocity contours and vectors in the model domain.The model was created in two-dimensions and meshed with about 15,000 quadratic elements.Convergence and stability of the solution were verified at a certain number of finite elements and iterations.It was found that as the angle of inclination of the roof increased,the mean static pressure on such roof has increased with an enlarged stagnation zone.The results show that a pitched roof of 30° has a much better heat transfer performance than one with 10°,20°,and 40° for same base building model height and Reynolds number.Good agreement was found between the experimental and computational results.