An investigation of turbulent accelerated flow along smooth prismatic chutes Hassan Ibrahim Mohamed Civil Engineering Department, Assiut University, Assiut, Egypt Keywords accelerated flow; chutes; computational fluid dynamics; pressure distribution. Correspondence H. I. Mohamed, Civil Engineering Department, Assiut University, Assiut 71516, Egypt. Email: hassanmohamed_2000@yahoo.com doi:10.1111/j.1747-6593.2012.00325.x Abstract Turbulent chute flow was investigated experimentally and numerically for various flow conditions. The Navier-Stokes equations are solved with the k - e turbulence model on a structured non-orthogonal grid. A method based on water continuity was used to calculate the movement of the water surface. Using an adaptive grid in the vertical direction, the location of the water surface was recalculated from an initially horizontal profile. After several iterations a steady solution emerged. The velocity distribution in longitudinal and vertical directions and pressure distribution along the chute were calculated. The numerical model was calibrated and verified using experimental data model studies. Reasonable agreement was found between the experimental results and that from the numerical model. Multiple-regression equation was developed for computing the water surface profile along chute. Introduction Many applications in hydraulic engineering deal with turbu- lent shooting flows. Typical examples are spillways, sewer systems and naturally occurring mountainous streams and rivers during heavy rainfall. Zhivotovskii et al. 2002 used chute as a component of specialised engineering systems for water treatment intended for improving water quality. The chute is assumed to have a uniform cross section through- out. Reinforced concrete is commonly used to protect the underlying soil from erosion. The flow in a chute is usually supercritical. The velocity of water increases rapidly as it passes over the control structure and becomes supercritical and increases with a drop in the elevation. An inappropriate design of the chute will lead to a notice- able increase in the water surface levels on the side walls as a result of the reflection and transverse interference of waves. Waves cause the non-uniform distributions of the dis- charge along the width and length of the chute. A strongly turbulent layer is only found along the bottom and walls. At a certain distance downstream, that is, during the acceleration of the flow along the chute, the depth of flow gradually decreases whereas the thickness of the turbulent boundary layer increases, until it, at the critical point, affects the entire depth of the flow. In spite of importance of chutes as hydrau- lic structures, little is known about the characteristics of flow along them because of the difficulties in measurements at the case of supercritical flow. The stream-wise profile of the flow surface is the main objective in the hydraulic design of chutes and stilling basins (Kirkgoz et al. 2009). The hydrodynamic characteristics of chute flow related to flow aeration, free surface profile and boundary layer development were studied, for example, by Ferrando & Rico 2002, Castro-Orgaz 2009, 2010 and Castro-Orgaz & Hager 2010. Reinauer & Hager 1996 pre- sented approach for the drawdown curve in chutes, where explicit relations for local flow depth and Froude number are given. Mohamed 2004 developed a simple method for com- puting pressure, energy and momentum correction coeffi- cients from the water surface profile for accelerating flow over block stones ramp. Nowadays, computational fluid dynamics (CFD) models are widely used in applied mathematics and fluid mechanics to simulate three-dimensional flow structures. In such situa- tions, rigorous testing of predicting mean and turbulent flow properties are accomplished using data obtained under con- trolled laboratory conditions (Nicholas 2001). In the following three-dimensional numerical model will be used for simulat- ing turbulent flow in a smooth chute channels. Model description The CFD code used for this investigation was developed by Olsen 1996. The model has been applied to a number of engineering situations including flow modelling for estima- tion of spillway capacity (Olsen & Kjellesvig 1998a), simulation of water and sedimentation in a sand trap (Olsen & Skoglund 1994), simulation of scour around a cylinder, (Olsen & Kjellesvig 1998b) and simulation of flow dynamics in a river with large roughness elements (Olsen & Stokseth 1995). The Water and Environment Journal. Print ISSN 1747-6585 71 Water and Environment Journal 27 (2013) 71–78 © 2012 The Author. Water and Environment Journal © 2012 CIWEM.