meanSupVelocityForce

Syntax

Defined in an fvOptions dictionary in the system folder of the CFD case. Can only be applied if solver is able to handle fvOptions.

momentumSource
{
    type            meanSupVelocityForce;
    active          yes;
    meanSupVelocityForceCoeffs
    {
        selectionMode   all;
        fieldNames      wordList;
        Ubar            vector;
        relaxation      scalar;
        twoPhase        Switch;
        alphaField      word;
        coupled         Switch;
        voidfractionField "voidfraction";
        alphaMin        scalar;
    }
}

  • selectionMode = selection mode (all or cellZoneSet)

  • fieldNames = list of vector field names this fvOption is applied to

  • Ubar = desired mean superficial velocity

  • relaxation = relaxation factor (optional)

  • twoPhase = indicator for several fluid phases (default: false)

  • alphaField = name of the phase indicator field, only read and mandatory if twoPhase true

  • coupled = indicator for presence of particles (default: false)

  • voidfractionField = name of the voidfraction field, only read if coupled true (default: “voidfraction”)

  • alphaMin = settings will only take place in cells with alpha >= alphaMin (default: 0)

Examples

momentumSource
{
    type            meanSupVelocityForce;
    active          yes;
    meanSupVelocityForceCoeffs
    {
        selectionMode   all;
        fieldNames      (U);
        twoPhase        true;
        alphaField      alpha.water;
        coupled         true;
        voidfractionField voidfraction;
        Ubar            (1 0 0);
        relaxation      0.9;
        alphaMin        0.9999;
    }
}

Description

The fvOption meanSupVelocityForce can be used to impose an average superficial velocity within a specific area (either defined by all when the whole domain is affected or the name of the according cellZone), while at the same time accounting for the resulting pressure drop. The fvOption can be used for fluid/fluid, fluid/particle and fluid/fluid/particle cases, whereas Ubar can only be imposed to one of the fluid phases. Application examples are periodic channel flow situations or pumps within the computational domain.

Note

Particularly for periodic channel flows, instabilities might occur at the air-water interface due to the large differences in the densities. For such cases a cutoff value alphaMin allows the user to restrict the affected area by means of a minimal phase fraction.

Restrictions

The implementation currently only handles kinematic pressure, i.e. works only for incompressible solvers. Moreover, the pressure gradient force modelled by gradPForce is neglected by this model.