Modeling Deep Open Channel Flow by VOF Method in Ansys Fluent
Hello everyone, this is Mohsen Seraj from Ozen Engineering, Inc. 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. In the second part, I will show you how to model the open channel flow with increased water depth.
Model Setup
We have two channels with slight changes in geometry, joining together at a certain point. The boundary conditions are similar for the inlets and outlets, with the top surfaces open to the air and the walls defined.
Steps to Set Up the VOF Method
- Activate the open channel flow and include implicit body force.
- Define two phases:
- Primary phase: Air (less density)
- Secondary phase: Water
- Set up phase interaction with surface tension included (0.072 N/m).
- Use continuum surface force for modeling.
- By default, k-omega SST is selected for turbulence modeling.
- No temperature or heat transfer is activated.
Boundary Conditions
- Inlet:
- Pressure inlet with default momentum settings.
- Activate open channel and define water level and velocity.
- Free surface level set to 10 cm (previously 30 cm).
- Outlet:
- Pressure outlet with default momentum settings.
- Set open channel conditions similar to the inlet.
- Bottom level set to -10 cm below the XZ plane.
- Top Faces: Open to air with zero gauge pressure.
Solution Methods and Controls
- Use PISO for pressure-velocity coupling.
- Presto must be used for VOF method pressure discretization.
- Second-order discretization for momentum and turbulence.
Monitoring and Reporting
- Define volume average for velocity and area-weighted average for outlet pressure.
- Set up reports for uniformity index and vortex average.
Initialization and Patching
The model is initialized from all zones or the inlet. Patching is used to define where water is present in the domain before starting the solution.
Animation and Visualization
- Define iso-surfaces for VOF to visualize the free surface.
- Create animations for velocity magnitude and other parameters.
- Set recording increments for animations.
Results and Analysis
After running the solution for over 10,000 time steps, the results show:
- Velocity and pressure profiles at the free surface.
- Mixing and merging of flows from two channels.
- Backward waves traveling toward the inlet.
- Pressure distribution and turbulence intensity.
Conclusion
This video provides an overview of setting up the model using the VOF method for open channel flow in ANSYS Fluent. It demonstrates the results such as flow mixing, pressure profiles, and turbulence intensity. Thank you for watching.
Modeling Deep Open 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.
In the second part, I will show you how to model the open channel flow with a deep water depth. As you can see, we have two channels with a slight change in geometry. They join together in this part, and we can see that we have two channels with a deeper water depth.
These are the two channels we will use, with a similar cross-section regarding to the boundary conditions. The inlets, outlets, top surfaces are open to the air, and the walls are solid. We have two channels with a deeper water depth, which is almost a simple geometry compared to the previous part.
We just want to see what happens when we have more depth in the channel. After creating the model in ANSYS Discovery, we start by activating the open channel flow and including the implicit body force by default. We have two phases for the VOF method: water and air.
The primary phase is usually air because it has less density, and the secondary phase is water, which we choose. To define water as a liquid, we come to the material for the fluid. Usually, only air is given by default, but we can define a new material from the ANSYS database.
For example, we can choose the water liquid and its given properties or change it if we want. We also need to set up the phase interaction between air and water. Surface tension is included with 0.072 Newton per meter, and we use continuum surface force for the modeling.
The volume of fluid method is set up by default with k-omega SST k-omega already selected. We can change it to k-omega if we want. We don't activate the energy equation because there is no temperature or heat transfer in this model.
For boundary conditions, we choose pressure inlet for the inlets and keep the momentum as is. For multiphase, we activate open channel and define the water level at the inlet and what the velocity is, and where the bottom of the channel is.
For the outlet, we use pressure outlet and keep the momentum as is. For multiphase, we select open channel and set it to the free surface level and the bottom level. The top faces are opened, and we leave it as is. We don't need to set it to open channel because they are open to the air.
For monitoring, we can choose volume average for the velocity, for example, to see the results. After setting the boundary conditions, we can go and check the methods.
We use a piece-wise linear method for the coupling of pressure and velocity, and presto must be used for the volume of fluid method for the pressure discretization. We can choose second-order discretization for the momentum and keep the controls for the rigid walls as is.
We can define the animation for the solution, for example, to see the velocity at the outlet surface. These are the steps to set up the volume of fluid method in ANSYS Fluent. Thank you for watching.
