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## 7.2 Turbulence models

The momentumTransport dictionary is read by any solver that includes turbulence modelling. Within that file is the simulationType keyword that controls the type of turbulence modelling to be used, either:

- laminar
- uses no turbulence models;
- RAS
- uses Reynolds-averaged simulation (RAS) modelling;
- LES
- uses large-eddy simulation (LES) modelling.

### 7.2.1 Reynolds-averaged simulation (RAS) modelling

If RAS is selected, the choice of RAS modelling is specified in a RAS sub-dictionary which requires the following entries.

- model: name of RAS turbulence model.
- turbulence: switch to turn the solving of turbulence modelling on/off.
- printCoeffs: switch to print model coeffs to terminal at simulation start up.
- <model>Coeffs: dictionary of coefficients for the respective model, to override the default coefficients.

Turbulence models can be listed by running a solver with the -listMomentumTransportModels option, e.g.

simpleFoam -listMomentumTransportModels

The RAS models used in the tutorials can be listed using foamSearch with the following command. The lists of available models are given in the following sections.

foamSearch $FOAM_TUTORIALS momentumTransport RAS.model

foamInfo buoyantKEpsilon

#### 7.2.1.1 Incompressible RAS turbulence models

For incompressible flows, the RAS model can be chosen from the list below.

- LRR
- Launder, Reece and Rodi Reynolds-stress turbulence model for incompressible flows.
- LamBremhorstKE
- Lam and Bremhorst low-Reynolds number k-epsilon turbulence model for incompressible flows.
- LaunderSharmaKE
- Launder and Sharma low-Reynolds k-epsilon turbulence model for incompressible flows.
- LienCubicKE
- Lien cubic non-linear low-Reynolds k-epsilon turbulence models for incompressible flows.
- LienLeschziner
- Lien and Leschziner low-Reynolds number k-epsilon turbulence model for incompressible flows.
- RNGkEpsilon
- Renormalization group k-epsilon turbulence model for incompressible flows.
- SSG
- Speziale, Sarkar and Gatski Reynolds-stress turbulence model for incompressible flows.
- ShihQuadraticKE
- Shih’s quadratic algebraic Reynolds stress k-epsilon turbulence model for incompressible flows
- SpalartAllmaras
- Spalart-Allmaras one-eqn mixing-length model for incompressible external flows.
- kEpsilon
- Standard k-epsilon turbulence model for incompressible flows.
- kOmega
- Standard high Reynolds-number k-omega turbulence model for incompressible flows.
- kOmegaSST
- Implementation of the k-omega-SST turbulence model for incompressible flows.
- kOmegaSSTLM
- Langtry-Menter 4-equation transitional SST model based on the k-omega-SST RAS model.
- kOmegaSSTSAS
- Scale-adaptive URAS model based on the k-omega-SST RAS model.
- kkLOmega
- Low Reynolds-number k-kl-omega turbulence model for incompressible flows.
- qZeta
- Gibson and Dafa’Alla’s q-zeta two-equation low-Re turbulence model for incompressible flows
- realizableKE
- Realizable k-epsilon turbulence model for incompressible flows.
- v2f
- Lien and Kalitzin’s v2-f turbulence model for incompressible flows, with a limit imposed on the turbulent viscosity given by Davidson et al.

#### 7.2.1.2 Compressible RAS turbulence models

For compressible flows, the RAS model can be chosen from the list below.

- LRR
- Launder, Reece and Rodi Reynolds-stress turbulence model for compressible flows.
- LaunderSharmaKE
- Launder and Sharma low-Reynolds k-epsilon turbulence model for compressible and combusting flows including rapid distortion theory (RDT) based compression term.
- RNGkEpsilon
- Renormalization group k-epsilon turbulence model for compressible flows.
- SSG
- Speziale, Sarkar and Gatski Reynolds-stress turbulence model for compressible flows.
- SpalartAllmaras
- Spalart-Allmaras one-eqn mixing-length model for compressible external flows.
- buoyantKEpsilon
- Additional buoyancy generation/dissipation term applied to the k and epsilon equations of the standard k-epsilon model.
- kEpsilon
- Standard k-epsilon turbulence model for compressible flows including rapid distortion theory (RDT) based compression term.
- kOmega
- Standard high Reynolds-number k-omega turbulence model for compressible flows.
- kOmegaSST
- Implementation of the k-omega-SST turbulence model for compressible flows.
- kOmegaSSTLM
- Langtry-Menter 4-equation transitional SST model based on the k-omega-SST RAS model.
- kOmegaSSTSAS
- Scale-adaptive URAS model based on the k-omega-SST RAS model.
- realizableKE
- Realizable k-epsilon turbulence model for compressible flows.
- v2f
- Lien and Kalitzin’s v2-f turbulence model for compressible flows, with a limit imposed on the turbulent viscosity given by Davidson et al.

### 7.2.2 Large eddy simulation (LES) modelling

If LES is selected, the choice of LES modelling is specified in a LES sub-dictionary which requires the following entries.

- model: name of LES turbulence model.
- delta: name of delta model.
- <model>Coeffs: dictionary of coefficients for the respective model, to override the default coefficients.
- <delta>Coeffs: dictionary of coefficients for the delta model.

The LES models used in the tutorials can be listed using foamSearch with the following command. The lists of available models are given in the following sections.

foamSearch $FOAM_TUTORIALS momentumTransport LES.model

#### 7.2.2.1 Incompressible LES turbulence models

For incompressible flows, the LES model can be chosen from the list below.

- DeardorffDiffStress
- Differential SGS Stress Equation Model for incompressible flows
- Smagorinsky
- The Smagorinsky SGS model.
- SpalartAllmarasDDES
- SpalartAllmaras DDES turbulence model for incompressible flows
- SpalartAllmarasDES
- SpalartAllmarasDES DES turbulence model for incompressible flows
- SpalartAllmarasIDDES
- SpalartAllmaras IDDES turbulence model for incompressible flows
- WALE
- The Wall-adapting local eddy-viscosity (WALE) SGS model.
- dynamicKEqn
- Dynamic one equation eddy-viscosity model
- dynamicLagrangian
- Dynamic SGS model with Lagrangian averaging
- kEqn
- One equation eddy-viscosity model
- kOmegaSSTDES
- Implementation of the k-omega-SST-DES turbulence model for incompressible flows.

#### 7.2.2.2 Compressible LES turbulence models

For compressible flows, the LES model can be chosen from the list below.

- DeardorffDiffStress
- Differential SGS Stress Equation Model for compressible flows
- Smagorinsky
- The Smagorinsky SGS model.
- SpalartAllmarasDDES
- SpalartAllmaras DDES turbulence model for compressible flows
- SpalartAllmarasDES
- SpalartAllmarasDES DES turbulence model for compressible flows
- SpalartAllmarasIDDES
- SpalartAllmaras IDDES turbulence model for compressible flows
- WALE
- The Wall-adapting local eddy-viscosity (WALE) SGS model.
- dynamicKEqn
- Dynamic one equation eddy-viscosity model
- dynamicLagrangian
- Dynamic SGS model with Lagrangian averaging
- kEqn
- One equation eddy-viscosity model
- kOmegaSSTDES
- Implementation of the k-omega-SST-DES turbulence model for compressible flows.

### 7.2.3 Model coefficients

The coefficients for the RAS turbulence models are given default values in their respective source code. If the user wishes to override these default values, then they can do so by adding a sub-dictionary entry to the RAS sub-dictionary file, whose keyword name is that of the model with Coeffs appended, e.g. kEpsilonCoeffs for the kEpsilon model. If the printCoeffs switch is on in the RAS sub-dictionary, an example of the relevant …Coeffs dictionary is printed to standard output when the model is created at the beginning of a run. The user can simply copy this into the RAS sub-dictionary file and edit the entries as required.

### 7.2.4 Wall functions

A range of wall function models is available in OpenFOAM that are applied as boundary conditions on individual patches. This enables different wall function models to be applied to different wall regions. The choice of wall function model is specified through the turbulent viscosity field in the 0/nut file. For example, a 0/nut file:

18dimensions [0 2 -1 0 0 0 0];

19

20internalField uniform 0;

21

22boundaryField

23{

24 movingWall

25 {

26 type nutkWallFunction;

27 value uniform 0;

28 }

29 fixedWalls

30 {

31 type nutkWallFunction;

32 value uniform 0;

33 }

34 frontAndBack

35 {

36 type empty;

37 }

38}

39

40

41// ************************************************************************* //

There are a number of wall function models available in the release, e.g. nutWallFunction, nutRoughWallFunction, nutUSpaldingWallFunction, nutkWallFunction and nutkAtmWallFunction. The user can get the full list of wall function models using foamInfo:

foamInfo wallFunction

Having selected the particular wall functions on various patches in the nut/mut file, the user should select epsilonWallFunction on corresponding patches in the epsilon field and kqRwallFunction on corresponding patches in the turbulent fields k, q and R.