Gamma Transition Models Reference

Properties

Convection

Controls the convection scheme.

• 1st-order: Selects the first-order upwind convection scheme.
• 2nd-order: Selects the second-order upwind convection scheme.

Cross-Flow Term

Controls whether to apply a correlation for stationary cross-flow instabilities. The correlation accounts for transition that is triggered by surface roughnesses whose height is in the order of micrometers.

When On, modifies the transition trigger function $F_{onset}$ (see Eqn. (1562)), which activates the production term in the equation for the transported intermittency $\gamma$. The default setting is Off.

Cross-flow parameters

Child node that provides the model constant C_scf, that is $C_{SCF}$ in Eqn. (1564), and the cross-flow inducing roughness height in meters h(m), that is $h$ in Eqn. (1574). Increasing the default values accelerates the cross-flow induced transition.

Freestream Turb. Intensity (only for the SA Gamma Transition model)

The coefficient $T_{U_L}$ , see Eqn. (1558).

Sigma_f

The coefficient ${\sigma }_f$, see Eqn. (1550).

ca2

The coefficient $C_{a2}$, see Eqn. (1556).

ce2

The coefficient $C_{e2}$, see Eqn. (1556).

Intermittency Minimum

The minimum value that the transported variable $\gamma$ is permitted to have. An appropriate value is a small number that is greater than the floating point minimum of the computer.

Secondary Gradients

Neglect or include the boundary secondary gradients for diffusion and/or the interior secondary gradients at mesh faces.

• On: Include both secondary gradients.
• Off: Exclude both secondary gradients.
• Interior Only: Include the interior secondary gradients only.
• Boundaries Only: Include the boundary secondary gradients only.

CTU1

The coefficient $C_{\mathrm{TU}1}$, see Eqn. (1558).

CTU2

The coefficient $C_{\mathrm{TU}2}$, see Eqn. (1558).

CTU3

The coefficient $C_{\mathrm{TU}3}$, see Eqn. (1558).

Conset1

The coefficient $C_{\mathrm{onset}1}$, see Eqn. (1555).

Initial Conditions

Intermittency

Scalar profile value to specify the transported variable $\gamma$.

Gamma Transition Solver

This solver controls the solution of the Gamma transition model in all the continua for which the model is activated.

For the transported variable $\gamma$ the basic steps that are involved in the solution update are as follows:

• Update boundary conditions.
• Compute the reconstruction gradients and cell gradients.
• Create the linear system of equations using the discretization methods that are described in the K-Omega model formulation.
• Compute the residual sum for monitoring convergence:
  $$R={\sum }_{\text{cells}}^{}\left|r\right|$$
• Solve the linear system.
• Update the transported variable field.

Under-Relaxation Factor

At each iteration, governs the extent to which the old solution is supplanted by the newly computed solution. The default value is 0.8. For the theoretical background, see Eqn. (920) in Finite Volume Discretization.

Reconstruction Frozen

When On, Simcenter STAR-CCM+ does not update reconstruction gradients with each iteration, but rather uses gradients from the last iteration in which they were updated. Activate Temporary Storage Retained in conjunction with this property. This property is Off by default.

Reconstruction Zeroed

When On, the solver sets reconstruction gradients to zero at the next iteration. This action means that face values used for upwinding (Eqn. (905)) and for computing cell gradients (Eqn. (917) and Eqn. (918)) become first-order estimates. This property is Off by default. If you turn this property Off after having it On, the solver recomputes the gradients on the next iteration.

Solver Frozen

When On, the solver does not update any quantity during an iteration. It is Off by default. This is a debugging option that can result in non-recoverable errors and wrong solutions due to missing storage. See Finite Volume Solvers Reference for details.

Temporary Storage Retained

When On, Simcenter STAR-CCM+ retains additional field data that the solver generates during an iteration. The particular data retained depends on the solver, and becomes available as field functions during subsequent iterations. Off by default.

Field Functions

Intermittency

The transported variable $\gamma$ , see Eqn. (1550).

Specific Dissipation Rate Reynolds Number

The specific dissipation rate Reynolds number defined as ${\mathrm{Re}}_{\omega }=\frac{\omega d^2}{\nu }$.

Turbulence Intensity

The turbulence intensity, defined as $I=\sqrt{2/3k}/U$.