Fluid Film Solver Reference

The Fluid Film solver lets you customize solver settings for segregated flow, film velocity, and film thickness. The fluid film solvers generally use the same techniques as the Segregated Flow solvers. Differences arise from the fact that these solvers work with film equations on surfaces, and film control volumes depend on the film distribution.

The Fluid Film solver incorporates the following solvers:

Fluid Film Multiphase Solver Properties

The Fluid Film Multiphase solver controls the solution update for the film flow velocities and film thickness.

Update Frequency

Controls the frequency of updating film flow velocities and film thickness. The options are:

  • First And Last Iteration

    Available for PISO Unsteady simulations only. This option is the default setting.

  • Last Iteration

    Available for PISO Unsteady simulations only. This option can be useful for simulations where bulk and film flow are loosely coupled.

  • Every Iteration

    For Implicit Unsteady and Steady simulations, this option is the only setting available. For PISO Unsteady simulations, this option can help to increase stability at the cost of increased computational runtime.

Fluid Film Segregated Flow Solver Properties

The Fluid Film Segregated Flow solver lets you adjust the Segregated Flow solver parameters specifically for the fluid film calculations.

Temporary Storage Retained
When activated, retains data from temporary storage at the end of the iteration. Examples include the ap coefficients, the residual, the corrections, the reconstruction gradients, and the cell gradients. These quantities become available as field functions during subsequent iterations.
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.

Film Velocity Solver Properties

The Film Velocity solver uses a form of the Segregated Flow Velocity solver for the fluid film. It solves the momentum conservation equation, Eqn. (2722).

Under-Relaxation Factor
At each iteration, this property governs the extent to which the newly computed film velocity supplants the old one. The default value is 0.7. When the PISO Unsteady model is selected, this value is always set to 1.

Film Thickness Solver Properties

The Film Thickness solver calculates the mass conservation equation (Eqn. (2721)) which is expressed in terms of film thickness corrections. This solver is equivalent to the Segregated Flow Pressure solver which calculates the mass conservation equation that is expressed in terms of pressure corrections.

Under-Relaxation Factor
At each iteration, this property governs the extent to which the newly computed film thickness field supplants the old one. The default value is 0.7. When the PISO Unsteady model is selected, this value is always set to 1.