### 4.1.8. Omega-Based Reynolds Stress Models

Some of the main deficiencies of the Reynolds stress models for the simulation of boundary layers are an inheritance from the underlying -equation. Particularly the accurate prediction of flow separation is problematic when the -equation is used. Furthermore, low-Reynolds number formulations for the -equation are usually complex and difficult to integrate, a deficiency that is exaggerated in combination with a Reynolds stress model formulation. In order to avoid these issues, a Reynolds stress model has been implemented that uses the -equation instead of the -equation as the scale-determining equation.

There are two types of SMC- model in CFX:

- Omega Reynolds Stress

- Baseline (BSL) Reynolds Stress

As the freestream sensitivity of the standard model does carry over to the Reynolds stress model, the BSL Reynolds stress model was developed, which is based on the -equation used in the BSL model, and is preferred over the Omega Reynolds stress model. This is the formulation recommended when using the -Reynolds stress model.

All variants of the -Reynolds stress model are combined with automatic wall treatment, which allows a flexible grid resolution near the wall. For details, see:

- Modeling Flow Near the Wall

- Omega-Based Reynolds Stress Models in the CFX-Solver Theory Guide

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