Segregated Flow Solvers Reference
For the Segregated Flow model, the solver solves the conservation equations of mass and momentum in a sequential manner. The non-linear governing equations are solved iteratively for the solution variables—one after the other.
The segregated solver employs a pressure-velocity coupling algorithm where the mass conservation constraint on the velocity field is fulfilled by solving a pressure-correction equation. The pressure-correction equation is constructed from the continuity equation and the momentum equations such that a predicted velocity field is sought that fulfills the continuity equation, which is achieved by correcting the pressure. This method is also called a predictor-corrector approach. Pressure as a variable is obtained from the pressure-correction equation. The solution update is controlled according to the SIMPLE algorithm.
The segregated solver has its roots in constant-density flows. Although it can handle mildly compressible flows and low Rayleigh number natural convection, it is not suitable for shock-capturing, high Mach number, and high Rayleigh number applications.
The following solvers and solver options are available:
Click on any link to see the available properties for each solver or solver option.
Segregated Flow
The segregated flow solver solves the integral conservation equations of mass and momentum in a sequential manner. This solver uses a pressure-velocity coupling algorithm where the mass conservation constraint on the velocity field is fulfilled by solving a pressure-correction equation.
- Implicit Scheme
- The following pressure-velocity coupling algorithms are available:
- SIMPLEꟷthe solution update is controlled by the SIMPLE algorithm. Available only if you select the Steady or Implicit Unsteady time model in the physics continuum.
- SIMPLECꟷthe solution update is controlled by the SIMPLEC algorithm. Available only if you select the Implicit Unsteady time model in the physics continuum. This algorithm is not fully compatible with multiphase simulations. You are advised to use it for single phase flow only.
- PISOꟷthe solution update is controlled by the PISO algorithm. Available only if you select the PISO Unsteady time model in the physics continuum.
- Freeze Flow
- When On, deactivates the flow solver solution update while allowing the solver to continue responding to other solvers. This property is Off by default.
- Enable Enhanced Stability Treatment
- When On, activates the Pressure Corrections and Velocity Corrections expert properties to increase the robustness of iterations for each time-step. This property is Off by default, making these expert properties unavailable.
- 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.
- 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.
- Pressure Corrections: Bad Cell Minimum Scaling
- Sets a scale factor for pressure corrections, for bad cells, and for cells that have a volume change lower than the acceptable limit. See Volume Change. The default value is 0.8.
- Pressure Corrections: Acceptable Cell Volume Change
- Defines a limit of acceptable volume change for the solver enhanced robustness treatment. See Volume Change. The default value is 0.001.
- Velocity Corrections: Maximum Unlimited Velocity
- Defines the value below which there are no damping corrections to velocity magnitude. The default value is 20 m/s.
- Velocity Corrections: Acceptable Velocity Increase Rate [<1]
- Defines an acceptable limit that reduces the rate of increase of velocity magnitude due to pressure corrections. (There is no limit for rate of decrease.) See the SIMPLE Solver Algorithm. The default value is 0.15.
- Continuity Initialization
- When Off, the solver uses the initial conditions that you have specified to solve the flow equations.
Velocity
The Velocity solver controls the under-relaxation factor and algebraic multigrid parameters for the momentum equations. More specifically, it solves the discretized momentum equation to obtain the intermediate velocity field.
- Under-Relaxation Factor
- In order to promote convergence, this property is used to under-relax changes of the solution during the iterative process. For steady flows, the default value is 0.7; for unsteady flows, the default value is 0.8. The under-relaxation is implemented in an implicit manner. For more information, see Finite Volume Discretization.
- Dynamic Local Under-Relaxation
- For unsteady flows, the time-derivative term in the momentum equation acts as a form of under-relaxation for the system of equations. Because of this, the user-defined under-relaxation factor can cause a higher level of under-relaxation than the solution requires. Dynamic Local Under-Relaxation causes the solver to compare the relaxation provided by the time derivative term of the momentum equation with the user-defined under-relaxation. The solver then modifies the actual under-relaxation applied based on the result of the comparison.
Pressure
The pressure solver controls the under-relaxation factor and algebraic multigrid parameters for the pressure correction equation. More specifically, it solves the discrete equation for pressure correction, and updates the pressure field.
- Under-Relaxation Factor
- At each iteration, this property governs the extent to which the newly computed solution supplants the old solution. This quantity is in Eqn. (939). For steady flows, the default value is 0.3; for unsteady flows, the default value is 0.2.
- Pressure Reference Location
- Provides a choice between using the automatic algorithm of Simcenter STAR-CCM+ for the reference location or providing it manually.