Spillway Transient CFD Simulation
ُSpillway Project Description
Spillways are structures used to pass excess water and floods from the top to the bottom of the dam. In fact, spillways are structures with a certain height that discharge excess water when the height of the water exceeds their height. There are different types of spillways, including ogee, step, side, lotus, tunnel, siphon, etc. spillways. The present problem simulates the flow of water through a spillway.
Since the modeled fluids are water and air, the two-phase flow model is used. To define the two-phase flow in this simulation, a two-phase VOF (volume of fluid) model is used; So its primary phase is air and its second phase is water. In this case, the height of the water level at the inlet is 0.155 m and the total height of the model is 0.306 m and considering that the height of the dam is 0.156 m.
The hydraulic level of water increases after colliding with the body of the dam, so the excess value is discharged from the top of the spillway to the outlet. The purpose of this project is to investigate the behavior of water flow after passing over a spillway in the presence of air. This simulation is transient and the solution process is performed in the time interval of 0.05 s with a time step of 0.001 s.
Spillway Geometry & Mesh
The 3-D geometry of the present model is designed using Design Modeler software. The present model includes a domain for water and airflow at a height of 0.306 m and a spillway at a height of 0.156 m. The following figure shows the geometry.
The meshing of the model has been done using ANSYS Meshing software and the mesh type is unstructured. The element number is 698691. The following figure shows the mesh.
Spillway CFD Simulation
To simulate the present model, several assumptions are considered:
- We perform a pressure-based solver.
- The simulation is unsteady.
- The gravity effect on the fluid is equal to -9.81 m.s-2 along the y-axis.
A summary of the defining steps of the problem and its solution is given in the following table:
|Standard wall function||near-wall treatment|
|Volume of fluid||Multiphase model|
|air – water||phases|
|on||implicit body force|
|Boundary conditions (Spillway)|
|Mass flow inlet||Inlet|
|0 kg.s-1||mass flow rate||air|
|4.1 kg.s-1||mass flow rate||water|
|1||backflow volume fraction||air|
|0||backflow volume fraction||water|
|stationary wall||wall motion|
|Solution Methods (Spillway)|
|modified HRIC||volume fraction|
|first-order upwind||turbulent kinetic energy|
|first-order upwind||turbulent dissipation rate|
|0 Pascal||gauge pressure||(Spillway)|
|0 m.s-1||velocity (x,y,z)|
|0||water volume fraction|
At the end of the solution process, two-dimensional and three-dimensional velocity, air and water volume fraction, and pressure contours, as well as path lines and velocity vectors, are obtained.
All files, including Geometry, Mesh, Case & Data, are available in Simulation File. By the way, Training File presents how to solve the problem and extract all desired results.
This ANSYS Fluent project includes CFD simulation files and a training movie.