The Turbulent Flow, SST Interface
The Turbulent Flow, SST (spf) interface () is used for simulating single-phase flows at high Reynolds numbers. The physics interface is suitable for incompressible flows, weakly compressible flows, and compressible flows at low Mach numbers (typically less than 0.3).
The equations solved by the Turbulent Flow, SST interface are the Reynolds-averaged Navier–Stokes (RANS) equation for conservation of momentum and the continuity equation for conservation of mass. Turbulence effects are modeled using the Menter shear-stress transport (SST) two-equation model from 2003 with realizability constraints. The SST model is a so-called low-Reynolds number model, which means that it can resolve the flow all the way down to the wall. The SST model depends on the distance to the closest wall. The physics interface therefore includes a wall distance equation.
The Turbulent Flow, SST interface can be used for stationary and time-dependent analyses.
When this physics interface is added, the following default nodes are also added in the Model Builder: Fluid Properties, Wall (the default boundary condition is No slip), and Initial Values.
Except where included below, see The Laminar Flow Interface and The Turbulent Flow, k-ε Interface for all the other settings.
Turbulence
A different turbulence model can be selected under Turbulence model. Laminar or creeping flow may simulated by changing the Turbulence model type to None.
The Turbulence model property disables the Neglect inertial term (Stokes flow) check box, and for 2D components also the Shallow Channel Approximation check box.
Wall Treatment
The SST model employs per default an Automatic wall treatment, which switches between a low-Reynolds-number formulation and a wall function formulation depending on how well resolved the flow is close to the wall. The automatic wall treatment gives a robust formulation that makes the most out of the available resolution.
Select the Low Re option in order to enforce resolution all the way down to the wall. This can be more accurate than the automatic wall treatment provided that the mesh is fine enough.
Include Transition Modeling
With this option enabled, the physics interface includes a local, correlation-based transition model. An additional transport equation for the intermittency is solved together with the SST transport equations which are modified to include transition effects. This option requires Low Re wall treatment.
Edit Turbulence Model Parameters
Turbulence model parameters are optimized to fit as many flow types as possible, but for some special cases, better performance can be obtained by tuning the model parameters. For this physics interface the turbulence model parameters are a1, β0∗, β1 ,β2 ,γ1 ,γ2, σk1, σk2, σw1, and σw2, and the transition model parameters (when Include transition modeling is enabled) are ce2, ca2, σγ, CTU1, CTU2, CTU3, CPG1, CPG2, CPG3, , , Ck, CSEP, .
Dependent Variables
The following dependent variables (fields) are defined for this physics interface:
•
Velocity field u and its components
•
Pressure p
•
Turbulent kinetic energy k
•
Specific dissipation rate om
•
Intermittency gamma (when Include transition modeling is enabled)
•
Reciprocal wall distance G
The SST interface requires a Wall Distance Initialization study step in the study previous to the Stationary or Time Dependent study step.
For study information, see Stationary with Initialization, Time Dependent with Initialization, and Wall Distance Initialization in the COMSOL Multiphysics Reference Manual.