Understanding the freeze flow field options

Freezing the flow field for steady state or transient analysis can speed up the coupled solver convergence, particularly when temperature change has a relatively small effect on the flow.

Note:

The freeze flow field options are optimized for natural convection problems.

Freeze flow field options in steady state analysis

You specify the freeze flow field options in steady state analysis in the Freeze Flow Field at Convergence for Steady State group of the 3D Flow Solver tab. When you select the Freeze Flow Field at Convergence check box, the flow solver freezes flow field equations (mass, momentum, energy, turbulence quantities, and mixtures equations) one by one as they reach the specified convergence criteria.

You can restart the resolution of the flow field equations by selecting the Restart Flow Field check box. The flow solver reactivates the flow field when the temperature change between the current iteration and the iteration when the flow was frozen is greater than the Restart Temperature Change value.

Freeze flow field options in transient analysis

You specify the freeze flow field options in transient analysis in the Freeze Flow Field for Transient group of the 3D Flow Solver tab.

When you freeze the flow field in transient analysis, the flow solver stops solving the mass and momentum equations when one of the specified criteria are met. The other flow field equations continue to iterate with the thermal solver.

These are the criteria for freezing and reactivating the flow field calculation:

Freeze Flow Field Based on Solution Evolution

This option freezes the flow field when either the difference between:

• The normalized velocity of two consecutive time steps is less than the Maximum Normalized Velocity Change value, or

• The normalized pressure of two consecutive time steps is less than the Maximum Normalized Pressure Change value.

Restart Flow Field

This option reactivates the flow field when the temperature change between the current timestep and the timestep when the flow was frozen is greater than the Restart Temperature Change value.

Freeze Flow Field at Specified Times

This option freezes the flow field at time step values that you specify in the Freeze Flow Field Specified Times text box.

Reactivate Flow Field at Specified Times

This option reactivates the flow field at time step values that you specify in the Reactivate Flow Calculation Specified Times text box.

The solver checks all the criteria at each time step.

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