
Overview
The shearstress transport (SST)  model was developed by Menter [ 224] to effectively blend the robust and accurate formulation of the  model in the nearwall region with the freestream independence of the  model in the far field. To achieve this, the  model is converted into a  formulation. The SST  model is similar to the standard  model, but includes the following refinements:
These features make the SST  model more accurate and reliable for a wider class of flows (e.g., adverse pressure gradient flows, airfoils, transonic shock waves) than the standard  model. Other modifications include the addition of a crossdiffusion term in the equation and a blending function to ensure that the model equations behave appropriately in both the nearwall and farfield zones.
Transport Equations for the SST

Model
The SST  model has a similar form to the standard  model:
and
In these equations, represents the generation of turbulence kinetic energy due to mean velocity gradients, calculated as described in Section 4.5.1. represents the generation of , calculated as described in Section 4.5.1. and represent the effective diffusivity of and , respectively, which are calculated as described below. and represent the dissipation of and due to turbulence, calculated as described in Section 4.5.1. represents the crossdiffusion term, calculated as described below. and are userdefined source terms.
Modeling the Effective Diffusivity
The effective diffusivities for the SST  model are given by
(4.534)  
(4.535) 
where and are the turbulent Prandtl numbers for and , respectively. The turbulent viscosity, , is computed as follows:
where is the strain rate magnitude and
(4.537)  
(4.538) 
is defined in Equation 4.56. The blending functions, and , are given by
where is the distance to the next surface and is the positive portion of the crossdiffusion term (see Equation 4.552).
Modeling the Turbulence Production
Production of
The term represents the production of turbulence kinetic energy, and is defined as:
(4.544) 
where is defined in the same manner as in the standard  model. See Section 4.5.1 for details.
Production of
The term represents the production of and is given by
(4.545) 
Note that this formulation differs from the standard  model. The difference between the two models also exists in the way the term is evaluated. In the standard  model, is defined as a constant (0.52). For the SST  model, is given by
(4.546) 
where
(4.547)  
(4.548) 
where is 0.41.
Modeling the Turbulence Dissipation
Dissipation of
The term represents the dissipation of turbulence kinetic energy, and is defined in a similar manner as in the standard  model (see Section 4.5.1). The difference is in the way the term is evaluated. In the standard  model, is defined as a piecewise function. For the SST  model, is a constant equal to 1. Thus,
(4.549) 
Dissipation of
The term represents the dissipation of , and is defined in a similar manner as in the standard  model (see Section 4.5.1). The difference is in the way the terms and are evaluated. In the standard  model, is defined as a constant (0.072) and is defined in Equation 4.524. For the SST  model, is a constant equal to 1. Thus,
(4.550) 
Instead of having a constant value, is given by
(4.551) 
and is obtained from Equation 4.539.
CrossDiffusion Modification
The SST  model is based on both the standard  model and the standard  model. To blend these two models together, the standard  model has been transformed into equations based on and , which leads to the introduction of a crossdiffusion term ( in Equation 4.533). is defined as
For details about the various  models, see Section 4.4.
Model Constants
All additional model constants ( , , , , , , , , and M ) have the same values as for the standard  model (see Section 4.5.1).