Finishing the Calculation

The following finishing conditions are offered by Flow Simulation:

• maximum number of refinements;

• maximum number of iterations;

• maximum physical time (for time-dependent problems only);

• maximum CPU time;

• maximum number of travels;

• convergence of the Goals.

The number of iteration per travel is calculates as follows:

where K = 2 and Ncv,fluid is the number of fluid cells.

• If the Fluid Flow option is enabled and the stationary or High Mach Number flow is considered:

  	(2)

  where K = 2 and Ncv,fluid is the number of fluid cells.

• If the Fluid Flow option is disabled and the Conduction option is enabled, T is set to 120 if the Radiation option is enabled; otherwise, it is set to 40.

• If the Fluid Flow option is disabled and the Conduction option is enabled, T is also set to 40.

In Flow Simulation you can select the finishing conditions that are most appropriate from your viewpoint to solve the problem under consideration, and specify their values. For the latter two conditions (i.e., for the maximum number of travels and the Goals convergence settings) Flow Simulation presents their default values (details are described below). You can also select the superposition mode for multiple finishing conditions in the Finish Conditions value cell: either to finish the calculation when all the selected finishing conditions are satisfied or when at least one of them is satisfied.

In any case, information on the finishing conditions due to which the calculation has finished is shown in the Monitor’s Log box.

The Goals convergence finishing condition is complex since it consists of satisfying all the specified Goals criteria. A specified Goal criterion includes a specified dispersion, which is the difference between the maximum and minimum values of the Goal, and a specified analysis interval over which this difference (i.e., the dispersion) is determined. The interval is taken from the last iteration rearwards and is the same for all specified Goals. The analysis interval is applied after an automatically specified initial calculation period (in travels), and, if refinement of the computational mesh during calculation is enabled, after an automatically or manually specified relaxation period (in travels or in iterations) since the last mesh refinement is reached. As soon as the Goal dispersion obtained in the calculation becomes lower than the specified dispersion, the Goal is considered converged. As soon as all Goals included in the Goals convergence finishing condition (by selecting them in the On/Off column) have converged, this condition is considered satisfied. The Goals not included into the Goals convergence finishing condition are used for information only, i.e., with no influence on the calculation finishing conditions.

Let us consider the Flow Simulation default values for the maximum number of travels and the Goals convergence settings in detail. These default (recommended by Flow Simulation) values depend on the Result resolution level either specified in the Wizard or changed by pressing the Reset button in the Calculation Control Options dialog box. For higher Result resolution levels the finishing conditions are tighter.

The default maximum number of travels depends on

• the type of the specified Goal (i.e., dynamic or diffusive);

  Note:

  The dynamic goals are: Static Pressure, Dynamic Pressure, Total Pressure, Mass Flow Rate, Forces, Volume Flow Rate, and Velocity. The diffusive goals are: Temperature, Density, Mass in Volume, Heat flux, Heat transfer rate, Concentrations, Mass Flow Rate of species, and Volume Flow Rate of species.

• the specified Result resolution level;

• the problem's type (i.e., incompressible liquid or compressible gas, low or high Mach number gas flow, time-dependent or steady-state).

• the problem's type (i.e., incompressible liquid or compressible gas).

The default Goals convergence settings are the default analysis interval, which is shown in the Finish tab of the Calculation Control Options dialog box, and the default Goals criterion dispersion values, which are not shown in the Calculation Control Options dialog box, but, instead, are shown in the Monitor’s Goal Table or Goal Plot table (in the Criteria column), since they depend on the values of the Goal physical parameter calculated in the computational domain, and therefore are not known before the calculation and, moreover, can change during it. In contrast, the Goals criterion dispersion values specified manually do not change during the calculation.

As for the automatically specified initial calculation period (measured in travels), it depends on the problem type, the Goal type, and the specified Result resolution level.

Note, that the Goal features have the following characteristics depending on their type:

• the manually specified analysis interval for the Goals convergence finishing criteria must be substantially longer than the typical period of the flow field oscillation (if it occurs);

• the Goals determined on solid/fluid interfaces or model openings, as well as the post-processor Surface Parameters, yield the most accurate and correct numerical information on flow or solid parameters, especially integral ones;

• Global Goals yield the most reliable information on flow or solid parameters, although they may be too general;

• the CPU time depends slightly on the number of the specified Goals, but, in some cases, vary substantially in the case of presence of a Surface Goal;

• Surface Goals and Volume Goals provide exactly the same information that may be obtained via the Surface Parameters and Volume Parameters post-processor features, respectively.