, these models naturally account for effects such as anisotropy due to strong swirling motion, streamline curvature, rapid changes in strain rate and secondary flows in ducts.
The Reynolds Stress Turbulence node is the placeholder object to allow selection of Reynolds Stress turbulence sub-models.
Reynolds stress transport (RST) models, also known as second-moment closure models, are the most complex turbulence models in STAR-CCM+. By solving transport equations for all components of the specific Reynolds stress tensor,, these models naturally account for effects such as anisotropy due to strong swirling motion, streamline curvature, rapid changes in strain rate and secondary flows in ducts.
The RST model carries significant computational overhead. Seven additional equations must be solved in three dimensions (as opposed to the two equations of a K-Epsilon model). Apart from the additional memory and computational time required for these equations to be solved, there is also likely to be a penalty in the total number of iterations required to obtain a converged solution due to the numerical stiffness of the RST equations.
The reasons that the RST model requires the solution of seven equations in three dimensions are as follows. The Reynolds stress tensor is symmetric, so that only six of the nine components are unique. In addition to the six RST equations, a model equation is also needed for the isotropic turbulent dissipation 
. This is the same equation as the one used in the Standard K-Epsilon model. In two dimensions, only four of the Reynolds stress components need to be evaluated, so the total number of equations is reduced by two.
The starting point for the development of RST models is generally the exact differential transport equation for the Reynolds stresses, which is derived by multiplying the instantaneous Navier-Stokes equations by a fluctuating property and Reynolds-averaging the product (see [49] for this exact equation). In the resulting equations, only the transient, convective and molecular diffusion terms require no modeling. The terms remaining to be modeled are the diffusion term, the dissipation term and, perhaps the greatest challenge, the pressure-strain term. Appropriate models for these terms have received much attention during the past few decades; some of them are reviewed in [50].
STAR-CCM+ has a choice of three different Reynolds stress transport turbulence models: