155 Numerical Estimation of Pressure Coefficients over Single and Multispan Duo Pitched Roof Greenhouses D.L. Kateris, T.A. Kotsopoulos, V.P. Fragos and Ch. Nikita-Martzopoulou Dept. of Hydraulics, Soil Sciences, and Agricultural Engineering Faculty of Agriculture Aristotle University of Thessaloniki Thessaloniki Greece Keywords: fluid mechanics, Navier-Stokes equations, finite elements, pressure coefficients, computational fluid dynamics Abstract The greenhouses have usually metal frame covered by glass or plastics and therefore are light structures, which make them sensitive to dynamic loads such as the wind load. The air flow over a greenhouse is a complex phenomenon. The pressure coefficients are used to calculate the wind load on the building’s roof. Although, the eurocode for wind actions EN 13031-1:2001 gives values for external pressure coefficients on the greenhouses, many manufacturers complain for these values because they lead to heavy structures of greenhouses with high construction costs. The proper design of the greenhouses would have to ensure not only the functionality and the static safety of the structure but also to keep the construction cost at low level. In the light of the above and taking into consideration that the adjustment of national regulations to eurocode is expected to be completed in 2011, the present work is focused on the calculation of the pressure coefficients on single and multispan duo pitched roof greenhouses. The study of an incompressible two- dimensional, steady, viscous air flow takes place in a hypothetical wind tunnel with the Navier–Stokes and continuity equations. The equations have been solved numerically, using the Galerkin Finite Element Method. The Reynolds numbers are varied from 0.02 to 2000 for all the structures. The numerical results of pressure coefficients are compared and discussed with data of eurocode’s for wind actions. The pressure coefficients given by the eurocode in the leeward side of the roof are close to the results derived from this numerical estimation, in most cases. However, in the windward side, the results indicated that a further segmentation of the pressure coefficients would be better. INTRODUCTION The air flow over a greenhouse structure is a complex and complicated phenomenon which mainly depends on the wind characteristics (speed, direction etc.), the geometry of the structure and the type of the greenhouse (single or a multispan). One of the main stress factors of the bearing structure of the greenhouse is the wind. For the calculation of the wind load, the external wind pressure coefficient is used. The wind pressure coefficient is obtained from the EN 13031-1:2001, which is specialized for greenhouses. However, those values given by eurocode lead to heavy construction which have an inverse effect on the construction cost. Therefore, further research is required in this area. Many researchers have conducted experiments either in full scale or in laboratory conditions in order to study the air flow over a greenhouse. Experimental full scale measurements have been carried out by Αldrich and Wells (1979), Pande Pramod et al. (1980), Richardson et al. (1997), Molina-Aiz et al. (2004) and Richards et al. (2007). While, experimental measurements in wind tunnel or channels have been carried out by Αcrivos et al. (1968), Castro and Dianat (1983), Antoniou and Bergeles (1988), Vassiliou et al. (2000), Robertson et al. (2002), Ginger and Holmes (2003), and Blackmore and Tsokri (2006). Proc. IS on GreenSys2011 Eds.: C. Kittas et al. Acta Hort. 952, ISHS 2012