Open channel junctions are so important in water conveyance networks. As a result, the researchers have been focusing on study of flow characteristics in these parts of water systems. Numerical simulation allows us to achieve the answer for engineering problems without encountering the experimental difficulty and with minimum cost. The aim of this study was, developing a 1D analytical model for simulating open channel junctions base on continuity, energy and momentum equations and some simple assumptions and comparing the experimental results in order to validation of analytical results. In experiments, side slope of main channel was 45 and 90 degrees. The studied variables were the ratio of depth at the junction. Investigation of results showed that increase of Froude number and inlet discharge ratio would lead to increase of turbulence which would decrease precision of analytical model. Also the increase of side slope of main channel caused less turbulence and more precision of the analytical model. In analytical model maximum reported error was about 15% for angle of 90 degrees, with relatively high discharge and depth in main inlet channel and minimum reported error was about 5% for angle of 45 degrees, with relatively low discharge and depth in main outlet channel.

Intake structures which are used as water diverting structures in open channels, rivers, and reservoirs are of the oldest issues of hydraulic engineering. In this study, a lateral pipe intake was proposed as a flow diversion structure provided in side walls of a channel, and its discharge characteristics and flow pattern was studied numerically using 3D CFD package, Flow-3D. The simulations have been performed for various parameters. The results showed that the lateral pipe intake with 90o angle has the highest efficiency among all of our simulation scenarios. The vortex and the separation zone in the lateral pipe intake were formed behind the pipe. Also, formation of the recirculation zone behind the lateral pipe intake can be affected by other parameters like inlet Froude number and transversal position of the pipe intake mouth. Furthermore, an equation was developed for the discharge coefficient in the lateral pipe intake. The computed discharges were within ± 15% of the observed ones.

To analyze flows in channel expansions and contractions, two-dimensional, depth-averaged, unsteady flow equations are solved by using the two-step Taylor-Galerkin scheme. The 2-D, depth-averaged equations are written in a fully conservative form. The solution algorithm is based on an explicit time integration procedure which exploits the conservative properties of the governing equations. The unsteady flow model is used to obtain steady flow equations by treating the time variable as an iteration parameter and letting the solution converge to the steady state. The results of the mathematical model are compared with experimental data and other models. The capability of the model for handling mixed super- and sub-critical flows in a channel transition is demonstrated.

A three-dimensional (3D) finite volume model with a novel adjustment scheme was developed to solve shallow water equations in open channels. An explicit finite volume method was used to discretize the governing equations in a boundary-fitted structured and collocated grid system. Because a simple second-order central scheme was used for spatial discretization and due to the occurrence of high Peclet numbers in open channel flows, some treatments were needed to reduce oscillation. Thus, a special adjustment scheme designed to minimize differences in the averaged free surface elevation and flow discharge in a 3D model and 1D flow data was applied to some cross-sections. The model was applied to simulate shallow water flow in a backwardfacing step, a meandering channel with 90° bends and a 180° bend channel. A comparison of the model results with available experimental and numerical data illustrated that the proposed numerical procedure decreases the numerical oscillations and increases the stability of the 3D numerical model in open channel flow modeling.

The recirculations are essential in river engineering because they form silting zones and favour the development of specific fauna and flora. This paper deals with the behaviour of the recirculation zones occurring downstream the sudden expansion of an open channel. An Acoustic Doppler Velocimeter is used to measure the flow details. The mean flow property such as the length of the recirculation, the average velocity field and velocity gradient are obtained. Then the self-similarity of the velocity profile is retrieved. The numerical simulation for the similar conditions are preformed with the CFD software STAR CCM+. When compared with the experiments, the two approaches correspond well in terms of length of recirculation zone and also regarding details such as the velocity gradient profiles. Finally, the eddy viscosity concept is tested and the turbulent viscosity coefficient are obtained along the stream wise axis for all flows.

The Prandtl second kind of secondary current occurs in any narrow channel flow causing velocity dip in the flow velocity distribution by introducing the anisotropic turbulence into the flow. Here, a study was conducted to explain the occurrence of the secondary current in the outer region of flow velocity distribution using a universal expression.Started from the basic Navier-Stokes equation, the velocity profile derivation was accomplished in a universal way for both smooth and rough open channel flows. However, the outcome of the derived theoretical equation shows that the smooth and rough bed flows give different boundary conditions due to the different formation of log law for smooth and rough bed cases in the inner region of velocity distribution. Detailed comparison with a wide range of different measurement results from literatures (from smooth, rough and field measured data) evidences the capability of the proposed law to represent flow under all bed roughness conditions.