An In-line separator CFD simulation helps us study devices that separate different substances from a fluid as it flows in a pipeline. These separators are used in many industries to remove unwanted materials from a fluid stream. A key component in this process is the axial-flow swirling generator, which is often used to make the separation of oil from water more efficient. A detailed phase separation Fluent analysis is the best way to see how this works.

This project focuses on using an Axial-flow swirling generator CFD model to remove oil from water inside a separator. Using a multiphase CFD approach allows us to test and improve these designs on a computer before building expensive physical equipment. To ensure our simulation is accurate, we based our work on the scientific reference paper: “Performance Characteristics of In-Line Oil Separator with Various Airfoil Vane Configurations of the Axial-Flow Swirl Generator [1]”.

• Referennce [1]: Je, Yeong-Wan, Jong-Chul Lee, and Youn-Jea Kim. “Performance characteristics of in-line oil separator with various airfoil vane configurations of the axial-flow swirl generator.” Processes5 (2022): 948.

Figure 1- Geometry of in-line separator and swirling generator created by Solidworks and ANSYS Spaceclaim

Simulation Process ( ANSYS Fluent Simulation: In-Line Separator & Swirl Generator Setup)

A big challenge in this In-line separator CFD project was the complex geometry. First, we carefully designed the generator’s blades using Solidworks software. Then, we imported this design into ANSYS Spaceclaim to combine it with the main separator body, creating the final geometry shown in Figure 1. Next, we created the mesh using ANSYS Fluent Meshing. We used poly-hexacore elements because they are very good for complex shapes like this one. In total, our mesh for this oil-water separation CFD has 3,310,421 cells with good quality.For the solver setup, we used the Reynolds Stress Model (RSM) to handle the turbulence. We chose this advanced model because the swirl generator creates a very complex, swirling flow that needs a powerful model to capture it accurately. To model the two different liquids (oil and water), we used the Eulerian Multiphase module. In this multiphase CFD setup, water is the primary phase and oil is the secondary phase. Using the correct drag model and surface tension values is also very important for getting accurate results.

Figure 2- Poly-hexacore elements around the swirling generator

Post-processing (Two-Phase Separator Performance Analysis)

Our In-line separator CFD research reveals complex flow patterns and shows exactly how the separation happens. The streamline results show that the axial-flow swirling generator is very effective, creating a strong, helical (corkscrew) flow pattern with tangential velocities as high as 2.5 m/s. This swirling motion creates powerful centrifugal forces that are key to the separation. A very significant finding is that these centrifugal forces are about three to four times stronger than the force of gravity. The RSM turbulence model successfully captures the complex secondary flows, especially behind the generator’s blades. This phase separation Fluent analysis shows that to get the best separation, the blade design must be optimized to create a strong swirl without causing a large pressure drop.

Figure 3-Oil Velocity Streamline

The volume fraction results give us clear proof of how well the oil-water separation CFD works. We can see clear layers of the two phases. The denser water phase (ρ ≈ 998 kg/m³) is pushed to the outer walls by the centrifugal force. Meanwhile, the lighter oil phase (ρ = 900 kg/m³) gathers in the center, reaching volume fractions above 0.85 in the core region. Our Eulerian multiphase simulation captures how the two liquids interact at their interface. The results show a balance between the separating centrifugal forces and the mixing turbulent forces. This Axial-flow swirling generator Fluent analysis provides very useful information for improving separator designs for many industrial applications, like in petroleum refining or wastewater treatment.

Figure 4- Volume fraction of a) water b) oil phase