Modeling Open Water Channel Flow by VOF Method in Ansys Fluent
Hello everyone, this is Mohsen Seraj from Ozen Engineering. I'm a senior application engineer for ANSYS CFD. In this video, I will discuss how to model open channel flow in ANSYS Fluent using the Volume of Fluid (VOF) method.
Model Overview
This is the model I developed in Discovery. As you can see, we have a trapezoid cross-section for the channel. There are two channels joining together into a larger channel. I extended the larger channel to ensure we observe the proper merging of flows from each of these two channels.
Geometry and Boundary Conditions
- Two inlets are defined.
- One outlet is defined at the bottom to set the bottom level.
- Walls are defined for the channel boundaries.
- The top surface is defined as open.
Flow and Meshing
I transferred the model as a watertight geometry workflow to ANSYS Meshing and then to ANSYS Fluent. In Fluent, I activated gravity in the y-direction for a transient simulation. The VOF method was activated with the option for open channel flow, using two phases: air and liquid water.
Material Properties
Using the material box in Fluent, I defined liquid water with specific density and viscosity. The primary phase is air, and the secondary phase is liquid water. This setup is typical when modeling air and water in the VOF method, as air is lighter with less density.
Phase Interaction
- Default interaction is set to none.
- Constant surface tension is considered between air and water at the free surface.
- Continuum surface force modeling is activated for surface tension.
Simulation Setup
The energy model is turned off as there is no energy transfer involved. For momentum, no special settings are required, and the open channel option is activated. The water level at the inlets is specified as 0.03 meters (30 centimeters), with a velocity of 1 meter per second.
Boundary Conditions
- Inlet: Water level of 0.03 meters, velocity of 1 m/s.
- Outlet: Pressure outlet with momentum extending to the inlet.
- Top surface: Open to air, considering gauge pressure.
Initialization and Patching
Initialization is done from the inlet, setting the initial water level to 30 centimeters throughout the domain. Patching is used to define the initial water region, named region_initial, based on the domain's dimensions.
Visualization and Results
Animations and scenes are created to visualize the flow, velocity, and pressure distribution. An ISO surface is defined where the volume of fluid for water is 0.5, indicating the interface between air and water.
Simulation Execution
- Time step: 5 milliseconds.
- Max iterations per time step: Default value.
- Simulation run: Approximately 9,000 to 10,000 time steps.
Results
Animations show the merging of flows, wave development, and velocity distribution. The results can be visualized using contours, vectors, and path lines to illustrate flow patterns and turbulence intensity.
Conclusion
This video demonstrates the setup of the VOF method for modeling flow analysis in open channels using ANSYS Fluent. Thank you for watching.
Modeling open water channel flow by VOF method in Ansys Fluent Hello everyone, this is Mohsen Seraj from Ozen Engineering. I'm a senior application engineer for ANSYS CFD. In this video, I want to talk about how to model open channel flow in ANSYS Fluent using the Volume of Fluid (VOF) method.
Here is the model I developed in Discovery. As you can see, we have a T-junction with two channels joining together to form a larger channel. I extended the larger channel to ensure we see the good merging of the flows coming from each of these two channels.
We have a large channel and a large channel. This is the two channels. I already defined the inlets, as you see these are two inlets here, and I have one outlet there at the bottom for defining the bottom level and walls here as you can see for the walls of the channel.
I called the top surface as open. I have already set up the flow and mesh. I transferred it as a watertight geometry workflow to ANSYS Meshing and then to ANSYS Fluent. Here it is ANSYS Fluent, and as you see, I already activated the gravity in the y-direction.
It is a transient simulation for the model. I activated the volume of fluid method with the option for open channel flow. The default number of phases is two: one for air and one for the liquid water.
I checked the implicit body forces, and we have two phases here: one for air and one for the liquid water. The most important things are the density and viscosity for the water. For the volume of fluid method, the primary phase is air, and the secondary phase is liquid water.
I considered a constant surface tension between the air and water at the free surface and activated the continuum surface force modeling for surface tension.
For initialization, I defined the velocity, volume average, volume average velocity for the whole interior, and pressure at the outlet to see if there are any unexpected results. I initialized the water level from the inlet.
Before running the solution or the calculation, I can define different contours or ISO surfaces to see what I want. I use a very low time step for the calculation.
After finishing the calculation, I can see the results, such as the free surface animation, the velocity at the free surface, and the pressure distribution. I can also use vectors or path lines to show the results for the contours.
I hope this video helps you understand how to set up the volume of fluid method for modeling open channel flow in ANSYS Fluent. Thank you for watching.
