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Numerical Investigation of Length and Thickness of Separation Zone after Sudden Change of Direction in Closed Sections Original Article, B6 Sadeghfam.S, Akhtari.A.A. Journal. Civil Eng. Urban. 2(1): 35-39. 2012. ABSTRACT: Separation phenomenan which is created in result of the inverse pressure gradient reduces the efficiency of the hydraulic systems. Due to eddy flows, analytical solution is not possible. In this paper, the relationship between the length and the thickness of the separation zone versus velocity variations has been investigated by using Fluent, in closed sudden change of direction in square sections with different divergence angles. First, to verify the accuracy of the numerical model, and some other factors such as turbulent model, the results of numerical model have been compared with experimental results in a sudden expansion at several sections. Based on the results of sudden expansion analysis, the turbulence model k-e (RNG) and steady flow mode are used in analysis of two dimensional bends. The results show that for the sharp curvature with central angle of 45 degrees regardless of flow velocity, separation in internal wall doesn't happen. For the sudden change of direction with a central angle of 45 to 90 degrees, flow separation is the function of divergence angles and flow velocity. In this study, the equations in terms of length and thickness of the separation are collected via abundant numerical analysis. Keywords: Separation, Inverse Pressure Gradient, Sudden Change of Direction, Fluent, Turbulent Model k-e (RNG) منبع: [Hidden Content] دانلود: [Hidden Content].,B6-35-39.pdf J. Civil Eng. Urban.,B6-35-39.pdf