### 4.1.3. The k-epsilon Model

One of the most prominent turbulence models, the (k-epsilon) model, has been implemented in most general purpose CFD codes and is considered the industry standard model. It has proven to be stable and numerically robust and has a well established regime of predictive capability. For general purpose simulations, the model offers a good compromise in terms of accuracy and robustness.

Within CFX, the turbulence model uses the scalable wall-function approach to improve robustness and accuracy when the near-wall mesh is very fine. The scalable wall functions enable solutions on arbitrarily fine near-wall grids, which is a significant improvement over standard wall functions.

While standard two-equation models, such as the model, provide good predictions for many flows of engineering interest, there are applications for which these models may not be suitable. Among these are:

- Flows with boundary layer separation.

- Flows with sudden changes in the mean strain rate.

- Flows in rotating fluids.

- Flows over curved surfaces.

A Reynolds stress model may be more appropriate for flows with sudden changes in strain rate or rotating flows, while the SST model may be more appropriate for separated flows. For details, see The k-epsilon Model in ANSYS CFX in the CFX-Solver Theory Guide.

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