Two-equation turbulence models have matured to a point where a consolidation seems desirable. The main models used in industrial CFD codes today are [14] (standard and realizable/RKE), [18,33,34] (SST, BSL, Wilcox) and to a lesser degree V2f [12] (different versions). The differences between the models are not fundamental, but can nevertheless have a strong impact on results. For boundary layers, the models differ mostly in their 'aggressiveness' to predict separation onset. Furthermore, in the very near wall region, models can predict vastly different results, especially for heat transfer simulations, due to their differences in wall-treatment. There are also noticeable differences for free shear flows, where each model tends to favor certain flows over others. Finally, different models feature different limiters, which typically do not affect the baseline flows, but can have substantial influence in complex applications.

ANSYS developed a new turbulence model family called Generalized (GEKO) model with the goal of turbulence model consolidation. GEKO is a two-equation model, based on the model formulation, but with the flexibility to tune the model over a wide range of flow scenarios. The key to such a strategy is the provision of free parameters which the user can adjust for specific types of applications without negative impact on the basic calibration of the model. In other words, instead of providing users flexibility through a multitude of different models, the current approach aims at providing one framework, using different coefficients to cover different application sectors. This will substantially simplify code usage for industrial CFD users. This approach also offers a much wider range of calibration capabilities than currently covered by switching between existing models. Finally, GEKO is (or will be made) compatible with all other options in the codes, so that there is no need to select any other model for compatibility or accuracy reasons.

Historically, the coefficients of turbulence models are exposed in the GUI to users (e.g. , , etc. in a model). However, this exposure is of little value, as most coefficients are linked to the basic calibration of the model (namely the calibration for the logarithmic law affecting e.g. flat plate simulations). Users can therefore not freely change these values without affecting such flows. In the GEKO model, free coefficients are introduced, which do not affect the logarithmic layer calibration and can therefore be tuned to achieve the desired model behavior. The GEKO model offers six free parameters – two of them aiming at wall bounded flows, two for the calibration of free shear flows, one coefficient to improve corner flow simulations (corner separation) and finally a curvature correction term.

The generic idea behind the model will be discussed. Not all details can be provided as the model is at present unpublished. However, the variability of the model will be demonstrated for a variety of generic flows and Best Practice Guidelines for optimal usage will be provided.

In order to keep the document compact, only a sketch of the geometry is provided for the test cases as well as a reference to the publication. This is sufficient, as the test cases are typically simple and it is only required to understand the basic flow challenge.