Iranian Rainwater Catchment Systems AssociationEnvironment and Water Engineering2476-36837320211023Numerical Study of the Effects of Non-Prismatic Floodplain Divergence Angle on Flow Velocity in the Cross Section of Compound ChannelsNumerical Study of the Effects of Non-Prismatic Floodplain Divergence Angle on Flow Velocity in the Cross Section of Compound Channels45446412653510.22034/jewe.2021.250562.1434FAMorteza ShokriAssist. Professor, Department of Civil Engineering, Kabodarahang Engineering Faculty, Bu-Ali Sina University, Hamedan, IranReza MehdipourM.E. Student, Department of Civil Engineering, Faculty of Engineering, Bu Ali Sina University, Hamadan, IranJournal Article20200928The formation of the secondary flows is caused by the non-prismatic nature of the main channel and floodplains in the compound channel and the intense interaction of the low-velocity flow of the floodplains in passing over the high-velocity flow of the main channel. So far, comprehensive studies on changing the divergence angle of floodplains have not been done as a numerical and physical model, and due to the effectiveness of this parameter, its study is necessary. In the present study, using the three-dimensional Ansys-Fluent model, simulation was performed based on the standard k-ε turbulence model and VOF method for the hydraulic flow in compound channel with divergent floods for five divergence angles of 3, 6, 9, 12 and 15° and in three sections of 2, 8 and 14 m. The boundary conditions used in this research were the input limit of the mass flow rate, the output boundary as a pressure outlet, the solid boundaries as a non-slip wall without roughness and the upper boundary of the channel as a non-slip wall without roughness. The results of accurately predicting the average depth velocity in the section Z = 14 m of the channel showed that in all sections of the channel, the modeling results were within the allowable error range defined for numerical models, indicating the appropriate matching of laboratory and simulation results. The results showed that the maximum velocity in the channel occurs with a divergence angle of 3° and the higher the divergence angle, the lower the velocity. Moreover, the maximum shear stress in the channel is with a divergence angle of 3° and the minimum shear stress is in the divergence angle is 15°. The lower the water angle, the higher the divergence angle, and the higher the divergence angle, the lower the water height.The formation of the secondary flows is caused by the non-prismatic nature of the main channel and floodplains in the compound channel and the intense interaction of the low-velocity flow of the floodplains in passing over the high-velocity flow of the main channel. So far, comprehensive studies on changing the divergence angle of floodplains have not been done as a numerical and physical model, and due to the effectiveness of this parameter, its study is necessary. In the present study, using the three-dimensional Ansys-Fluent model, simulation was performed based on the standard k-ε turbulence model and VOF method for the hydraulic flow in compound channel with divergent floods for five divergence angles of 3, 6, 9, 12 and 15° and in three sections of 2, 8 and 14 m. The boundary conditions used in this research were the input limit of the mass flow rate, the output boundary as a pressure outlet, the solid boundaries as a non-slip wall without roughness and the upper boundary of the channel as a non-slip wall without roughness. The results of accurately predicting the average depth velocity in the section Z = 14 m of the channel showed that in all sections of the channel, the modeling results were within the allowable error range defined for numerical models, indicating the appropriate matching of laboratory and simulation results. The results showed that the maximum velocity in the channel occurs with a divergence angle of 3° and the higher the divergence angle, the lower the velocity. Moreover, the maximum shear stress in the channel is with a divergence angle of 3° and the minimum shear stress is in the divergence angle is 15°. The lower the water angle, the higher the divergence angle, and the higher the divergence angle, the lower the water height.http://www.jewe.ir/article_126535_4e48ebe71af539bd39df9d9f1bf5e054.pdf