Large Eddy Simulation (LES) is a powerful tool in the modeling of hydrocyclones, which are widely used by ANSYS users for particle separation based on size and density. Unlike traditional RANS models, LES resolves the largest turbulent scales. It offers a more accurate depiction of the multiphase flows within hydrocyclones. This includes the swirling flow that generates centrifugal forces essential for particle separation, as well as the formation of an air core when outlets are exposed to the atmosphere. While computationally more expensive than RANS simulations, LES has demonstrated superior capabilities for the mean flows in cyclone separators. Besides, using the LES model requires a massive study of papers. Thus, the current simulation relies on several reference papers, but on top of them, the study titled “ Multiphase modeling of hydro cyclones – prediction of cut-size” led the simulation [1].”

• Reference [1]: Brennan, Matthew S., Mangadoddy Narasimha, and Peter N. Holtham. “Multiphase modelling of hydrocyclones–prediction of cut-size.” Minerals Engineering4 (2007): 395-406.
• Reference [2]: Brennan, M. “CFD simulations of hydrocyclones with an air core: Comparison between large eddy simulations and a second moment closure.” Chemical Engineering Research and Design6 (2006): 495-505.
• Reference [3]: Narasimha, M., M. S. Brennan, and P. N. Holtham. “CFD modeling of hydrocyclones: Prediction of particle size segregation.” Minerals Engineering39 (2012): 173-183.

Figure 1: A real industrial hydrocyclone

Simulation Process

A precise geometric representation of the hydrocyclone, including its feed port, main body, and vortex finder, was developed using a three-dimensional model using Design Modeler. It then meshed carefully in ANSYS Meshing, resulting in an 1197968-cell structured grid (See Fig. 2). It is of the necessity in order to use Large Eddy Simulation (LES). In this work, the turbulence was resolved using large eddy simulation (LES) for the mixture, and phase segregation was modeled using the Eulerian multiphase model, considering the Granular theory approach for the dispersed phase. So the Transient (unsteady) solver as well. Needless to say, the RANS turbulence models must initially solve flow equations prior to LES.

Figure 2: Outline of structured grid over LES hydrocyclone

Post-processing

The LES results for the hydrocyclone reveal some fascinating fluid dynamics at play. Looking at the velocity contour (Fig.3), we can see a striking contrast between the fast-moving fluid near the walls and the slower central region. This pattern is crucial for the cyclone’s operation – it’s what drives the separation process. The highest speeds, reaching about 8.6 m/s, are concentrated along the conical section and near the inlet. Meanwhile, the core, especially around the vortex finder, shows much lower velocities. This velocity difference creates the centrifugal effect that sorts particles based on their size and density.

From an engineering standpoint, the sharp velocity gradients we’re seeing between the outer and inner flows suggest intense shear zones – that’s where the real action happens regarding particle separation. The cone shape seems to be doing its job, ramping up the fluid speed as it narrows. However, the sluggish flow in the vortex finder area might be a weak spot. Maybe adjusting its dimensions or shape could keep the momentum going and enhance overall efficiency. This is why the Large Eddy Simulation (LES) technique proves its capability to reveal sharp boundaries.