Wall Distance Model Reference

Wall Distance Properties

Reference Values

Minimum Allowable Wall Distance

The wall distance algorithm has been developed to return a positive definite value for almost all cell shapes. However it is possible that some degenerate cells, such as boundary sliver cells, could return a value that is close to zero. Since turbulence models and wall functions require a non-zero value, this could cause numerical problems. For this reason, the minimum allowable wall distance limits the value of the wall distance in the continuum. The default value is 1.0E-6 m.

If the wall distance is limited in one or more cells, a warning message is displayed. In this case, investigate the cause and attempt to remedy the situation.

Wall Distance Solver Properties

This solver controls the wall distance computation for the Implicit Tree wall distance method in all the continua for which the model is activated.

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.

Verbosity

Allows you to choose how much information Simcenter STAR-CCM+ reports in the Output window while the simulation is running. This property is useful for debugging problems when they occur. The only valid entries are 0 (default), 1, and 2:

• 0 = None: Leaves output at its default.
• 1 = Low: Displays CPU time statistics across cores for calculating the wall distance. It reports the mean, maximum, and minimum elapsed times in seconds.
• 2 = High: Displays CPU time statistics (see low verbosity) and memory usage statistics across cores. This entry allows you to evaluate the memory consumption of all server processes that are relevant to the wall distance calculation:
  • max process peak—that is the maximum resident memory usage across cores.
  • max host peak—that is the maximum memory that is used on a node.
  • accumulated peak—that indicates the rough scalability in terms of required memory.

PDE Wall Distance Solver Properties

This solver controls the wall distance computation for the PDE wall distance method in all the continua for which the model is activated.

Maximum Iteration

Sets the maximum number of iterations the solver can use. The default is 10.

Solver Tolerance

Specifies the total relative solver residual. The default value is 0.01.

Under-Relaxation Factor

In order to promote convergence, this property is used to under-relax changes of the solution during the iterative process. If residuals show solution divergence and do not decrease, reduce the under-relaxation factor.

Verbosity

Allows you to choose how much information Simcenter STAR-CCM+ reports in the Output window while the simulation is running. This property is useful for debugging problems when they occur. The only valid entries are 0 (default) and 1:

• 0 = None: Leaves output at its default.
• 1 = Low: Displays convergence history for wall distance and CPU time information.

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.

Under-Relaxation Factor Ramp

The PDE Wall Distance > Under-Relaxation Factor Ramp node allows you to set and control a linear ramp for under-relaxation. For details, see Under-Relaxation Factor Ramp Reference.

AMG Linear Solver

The PDE Wall Distance > AMG Linear Solver node allows you to set the algebraic multigrid parameters for the turbulence solver. For details, see Algebraic Multigrid and AMG Linear Solver Properties.

Field Functions

Wall Distance

Scalar field that represents the normal distance $y$ from the cell centroid to the nearest wall face with a non-slip boundary condition calculated by the Wall Distance solver.