Segregated MMP Solver Reference

The Segregated MMP Solver controls the solution update for the phase volume fractions. More specifically, it solves the discretized volume-fraction conservation equation for each phase that is present in the flow.

Segregated MMP Solver Properties

The properties in the Expert category are used in a temporary debug situation, at the expense of simulation accuracy and memory usage. It is recommended that you do not change any of these properties unless you are thoroughly familiar with the discretization techniques used in Simcenter STAR-CCM+.

Note

The Segregated MMP solver does not have a Solver Frozen property. If you want to prevent any update of the volume fraction field, activate the Freeze Flow property in the Segregated Flow solver.

Solution Strategy

Controls the strategy for volume fraction transport in solver iterations. The options are:

  • Single-Step

    When this solution strategy is selected, the Segregated MMP solver performs a single step per time-step. This is the default. See Single-Step Solver Properties.

  • Implicit Multi-Step

    When this solution strategy is selected, the Segregated MMP solver performs multiple steps per time-step.

    The implicit multi-step solver is not bound to a strict CFL condition and volume fraction transport does not limit the global time step size. With this option, a fixed user-specified number of implicit sub-steps are used for the solution of the volume fraction transport equation. Additionally, the implicit multi-step solver allows the interface to smear when the CFL number exceeds the HRIC limit.

    If the global time-step size is small enough to resolve physics sufficiently well, but too large to fulfill HRIC stability requirements, implicit sub-stepping with an appropriate number of sub-steps is a cheaper alternative to reducing the global time-step size.

    The corresponding child node lets you specify the appropriate settings. See Implicit Multi-Step Solver Properties.

    Multi-stepping is compatible with the Implicit Unsteady solver using first-order Temporal Discretization. Multi-stepping is not compatible with second-order Temporal Discretization.

    NoteYou are not advised to use multi-stepping with the Steady model. For steady-state simulations use the Single-Step solution strategy.
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.
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.

Single-Step Solver Properties

The Segregated MMP Single-Step Solver

Under-Relaxation Factor
At each iteration, this property governs the extent to which the newly computed solution supplants the old solution.

When the Implicit Unsteady model is selected, the default value is 0.9.

Implicit Multi-Step Solver Properties

The Segregated MMP Implicit Multi-Step solver.

Under-Relaxation Factor

At each iteration, this property governs the extent to which the newly computed solution supplants the old solution at each sub-step.

When the Implicit Unsteady model is selected, the default value is 0.9.

Number of Steps

The specified fixed number of implicit sub-steps. The specified number of steps is not bound to a strict CFL number limitation near the interface. Hence, when the sub-stepping CFL number exceeds the HRIC limit, interface smearing is allowed without any adverse effects on mass conservation.

Increasing the number of sub-steps increases memory requirements as well as computational efforts. The allowed range for number of steps is from 1 to 20. The default value is 3. If the number of steps is set to one, the solution is similar to the one from the Single-Step solver strategy. Corresponds to N i m p ⁡ in Eqn. (2628).