Understanding how different liquids move through materials with tiny holes, like rocks or filters, is a huge challenge in engineering. This process, known as Mixture Transport In Porous CFD, is vital for many important jobs, from cleaning up the environment to getting more oil out of the ground. It gets very tricky when the material itself isn’t the same everywhere. The ease with which a fluid can flow, a property called permeability, can change from one spot to another. Standard computer simulation tools can’t handle this easily. To solve this problem, we need to add special instructions using a User-Defined Function (UDF). This custom code tells the computer exactly how the material properties change. Our study uses ANSYS Fluent with a powerful UDF to see what happens when a mix of oil and water travels through a porous material with this special kind of changing permeability.

Simulation Process: Modeling Variable Permeability with a Custom UDF

For our Mixture Transport In Porous Fluent simulation, we started with a simple 2D rectangle to act as our channel. We then divided it into a neat, structured grid of many small boxes to ensure our calculations would be accurate. Since we were studying a mix of oil and water flowing together, we used the Mixture multiphase model in ANSYS Fluent. The most important part of our simulation was creating a custom piece of code, a User-Defined Function (UDF). The purpose of this Mixture Transport UDF CFD was to control a key property of the porous material called “Viscous Resistance,” which is how Fluent understands permeability. Our UDF made this resistance change depending on the (x,y) position in the channel, following a specific mathematical rule. This allowed us to perfectly model a porous material that is not the same everywhere. The permeability is governed by the following relation:

Post-processing: CFD Analysis of Flow Velocity and Phase Separation

The simulation brings to life the journey of the oil and water mixture, starting with its speed. Figure 1 beautifully reveals the classic flow pattern inside the channel. A bright red streak running down the middle shows where the fluid moves the fastest, reaching a top speed of 0.46 m/s. This happens because the fluid in the center is far away from the walls and can flow freely. Near the top and bottom walls, however, the fluid is shown in blue, meaning it is moving very slowly. The walls create friction that “grabs” the fluid, slowing it down. The perfect, symmetrical shape of this speed profile is a great sign, confirming that the basic fluid flow part of our simulation is working exactly as expected.

Figure 1: Velocity contour from the Mixture Transport CFD simulation, showing the classic parabolic flow profile in the porous channel.

The story gets more interesting when we look at how the oil and water separate from each other, as shown in Figure 2. Here, we can see that the lighter oil (shown in red) has floated to the top, while the heavier water (blue) has settled toward the bottom, a natural effect of gravity. But something else is happening that is controlled by our special UDF. If you look closely at the red oil layer at the top, you will see it gets thicker as it moves from left to right. This change is not random; it is a direct result of the changing permeability CFD that our UDF created. The UDF makes some parts of the channel easier for the oil to flow through than others, causing it to build up in certain areas. The most important achievement of this Mixture Transport UDF CFD analysis is its ability to show how spatially varying permeability, controlled by the UDF, directly influences the separation and distribution of the oil and water phases. This validates our model as a powerful tool for predicting fluid behavior in complex, real-world porous materials like oil reservoirs or geological formations.

Figure 2: Oil volume fraction from the Mixture Transport In Porous Fluent analysis, demonstrating gravity-driven phase separation influenced by variable permeability.