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Spillway (Wide-Edge) with Lateral Slope, Two-Phase Flow

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In this analysis, the flow inside a wide-edge spillway is investigated.

This ANSYS Fluent project includes Mesh file and a Training Movie.

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A wide-edge spillway is a cascading structure with a long horizontal crown in the direction of the flow so that the error due to the distribution of hydrostatic pressure on it can be neglected due to the acceleration of the radial flow. These overflows operate in such a way that the flow upstream will be subcritical and supercritical on the spillway itself. As a result, a flow control section is created above it. One of the characteristics of such overflows is that in a short distance from the overflow crown, the flow lines are almost parallel.

In this type of spillway, the edge of the spillway is wide enough and has a considerable size compared to other dimensions. The crowns of the overflow edges are wide, horizontal or have a special curvature. Although they are also used to measure discharge, they are mostly used as dam overflows and sometimes as the dam itself (if water is allowed to pass through it) and can be used to store large volumes of water when necessary.

Project description

In this analysis, the flow inside a wide-edge spillway is investigated. It should be pointed out that there is an elevation difference between the main and sub-channel for reasons like storing a portion of flowing water. The RNG k-epsilon model is used for solving turbulent flow equations. Also, multiphase VOF model is activated to simulate two phases of water and air inside the open channel. The water enters the open channel with a mass flow rate of 65Kg/s and enters the second channel after colliding with middle section of the spillway.

spillwayGeometry and mesh

The geometry of this project is designed and meshed inside ANSYS design modeler and meshed in ANSYS meshing. The meshes type used for this geometry is structured and the total number of elements is 981900.

spillwayspillwaySpillway CFD simulation settings

The key assumptions considered in this project are:

  • Simulation is done using pressure-based solver.
  • The present simulation and its results are considered to be steady and do not change as a function time.
  • The effect of gravity has been taken into account and is equal to -9.81 in Y direction.

The applied settings are recapitulated in the following table.

Viscous model k-epsilon
k-epsilon model RNG
near wall treatment standard wall function
Multiphase VOF
Primary phase Air
Secondary phase water
Boundary conditions
Water inlet Type Mass flow inlet
Mass flow rate 65 Kg/s
Open channel
Free surface level 0.08 m
Bottom level 0 m
Density interpolation method From neighboring cell
Outlets Pressure outlet
wall motion stationary wall
Solution Methods
Pressure-velocity coupling   SIMPLE
Spatial discretization pressure PRESTO!
momentum second order upwind
Volume fraction first order upwind
turbulent kinetic energy first order upwind
turbulent dissipation rate first order upwind
Initialization method   Standard
gauge pressure 0 Pa
velocity 0 m/s-1
Turbulent kinetic energy 1 m2/s2
Turbulent dissipation rate 1 m2/s3
Water volume fraction 0

Spillway Results

We can see in the water volume fraction contour that due to the existence of height difference and the lack of any inlet flow inside the sub-channel, the water volume fraction has values other than zero in the upper part of the sub-channel. After the simulation process, we extracted and presented 3D contours of pressure, velocity, volume fractions, etc.

Mesh file is available in this product. By the way, the Training File presents how to solve the problem and extract all desired results.


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