Welcome to the ANSYS Fluent Free Surface Tutorial
In this tutorial, I will demonstrate how to model a microfluidics device. The green part you see here is the reservoir, which serves as the chamber where the sample enters. It connects to microfluidic channels that expand and lead to an exit at the end. The model already includes the mesh, so we will focus on setting up the model.
Model Setup
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Outline View:
- Select pressure-based under General.
- The velocity formulation is set to absolute. These are default settings.
- For a free surface problem, select transient simulation.
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Physics Selection:
- Enable multi-physics by right-clicking and editing.
- Ensure the model has a volume of fluids with default settings:
- Volume fraction parameters: explicit
- Volume fraction cutoff: 1e-6
- Courant number: 0.25
- Define two Eulerian phases: air and liquid (water).
- Set the surface tension coefficient for water to 0.072 dynes.
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Laminar Flow:
- Right-click on viscous and select laminar.
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Materials:
- Focus on fluids since this is a fluid model.
- Define two fluids: air and water liquid.
- Use default density and viscosity for water from the Fluent database.
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Cell Conditions:
- Define two regions: cassette and slump (reservoir).
- For both regions, ensure the phase is set to mixture.
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Boundary Conditions:
- Types: internal, outlet, and walls.
- Set outlet pressure to atmospheric (gauge pressure: 0).
- Ensure pressure outlet is selected for all outlets.
- Set contact angles for walls:
- Reservoir: 45 degrees (hydrophilic)
- Chamber: 90 degrees (neutral)
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Initialization:
- Create a cell register for the free surface level.
- Use coordinates to define the initial liquid level.
- Initialize the model with the patch.
Solution Setup
- Double-click on methods and select default settings:
- Simple method
- Spatial discretization: least square cell-based
- Initialize the problem using the patch.
Simulation and Results
For this transient simulation, 20 iterations are usually sufficient. The simulation shows the progression of the fluid, where red represents the liquid and blue represents air. As time progresses, the liquid displaces the air, filling the chamber favorably due to the hydrophilic contact angle.
Thank you for your attention. I look forward to showing you more capabilities of ANSYS Fluent.
Welcome to the ANSYS Fluent Free Surface tutorial. In this example, I will show you how to model a microfluidics device. What you see over here is basically the reservoir, which is the green part. This is the chamber where the sample would enter.
It's connected to these microfluidic channels that expand and then you have an exit at the end here. So this model already comes in with the mesh. We will focus on how to set up the model. The first thing we need to do is to go through the outline view.
Under general, select pressure-based and the velocity formulation is absolute. These are all the defaults. In the free surface problem, it's a transient simulation, so click on transient. Next, select types of physics. We want to use free surface and laminar flow.
Turn on multi-physics, and set the volume of fluids with volume fraction parameters explicit and the volume fraction cutoff at 1e- 6. There are two phases: air and liquid, which we will define as water. The surface tension coefficient for water is 0.072 dynes.
On the materials tab, we have fluids and solids. Since this is only a fluid model, ignore solids and go into fluids. Define the two fluids: air and water. Next, define the cell conditions. There are two regions: the cassette and the slump (inlet or reservoir).
For selecting the right properties, double right-click and edit. Set the reference frame as default and the phases as a mixture. Do the same for the slump and take the defaults. Move on to boundary conditions. There are three types: internal, outlet, and walls.
For outlets, set the outlet pressure at the end, the other outlet as air, and the sample as open to air. Set the contact angle for the walls based on the material. Lastly, set up the location for where the liquid will start.
Go to adapt, select manual, and create a cell register for the free surface level. This patch is needed during initialization. Set up the solution and initialize the problem. Now, we can run the transient simulation and observe the progression of the fluid as it moves.
The red color represents the liquid, and the blue represents air. As time progresses, the liquid is displacing air and filling the device. The displacement is favorable because the contact angle is hydrophilic. Thank you for your attention.
I look forward to showing you more on what you can do with the ANSYS Fluent.
