## Chapter 4: Turbulence and Near-Wall Modeling

This chapter describes:

- Turbulence Models

- Modeling Flow Near the Wall

Turbulence models are used to predict the effects of turbulence in fluid flow without resolving all scales of the smallest turbulent fluctuations. For details, see Turbulence Models in the CFX-Solver Theory Guide.

A number of models have been developed that can be used to approximate turbulence based on the Reynolds Averaged Navier-Stokes (RANS) equations. Some have very specific applications, while others can be applied to a wider class of flows with a reasonable degree of confidence. The models can be classified as either eddy-viscosity or Reynolds stress models. The following turbulence models based on the RANS equations are available in ANSYS CFX and are described on the following pages:

- Eddy-viscosity models:

  - Zero equation model.

  - Standard model.

  - RNG model.

  - Standard model.

  - Baseline (BSL) zonal based model. This model can only be selected through Expert Control Parameters.

  - SST zonal based model.

  - model. This model can only be selected through Expert Control Parameters.

  - Curvature correction for two-equation models.

- Reynolds stress models (RSM):

  - Launder, Reece and Rodi Isotropization of Production model (LRR Reynolds Stress).

  - Launder, Reece and Rodi Quasi-Isotropic model (QI Reynolds Stress).

  - Speziale, Sarkar and Gatski (SSG Reynolds Stress).

  - SMC- model (Omega Reynolds Stress).

  - Baseline (BSL) Reynolds stress model.

  - Explicit Algebraic Reynolds stress model (EARSM).

CFX also provides the Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) turbulence models. This class of turbulence models is not based on the RANS equations.

All turbulence models in CFX use advanced wall functions to model near-wall flow. For details, see Modeling Flow Near the Wall.

In order to predict transition, three different transition models of varying complexity are available in ANSYS CFX; see CFX Transition Model.

Information on turbulence modeling for multiphase flow is available in Turbulence Modeling in Multiphase Flow.

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