voidfractionModel_bigParticleVoidFraction command


Defined in couplingProperties dictionary.

voidfractionModel bigParticle;
    maxCellsPerParticle number1;
    alphaMin number2;
    weight number3;
    porosity number4;
  • number1 = maximum number of cells covered by a particle (search will fail when more than number1 cells are covered by the particle)
  • number2 = minimum limit for voidfraction
  • number3 = (optional) scaling of the particle volume to account for porosity or agglomerations.
  • number4 = (optional) diameter of the particle’s representation is artificially increased according to number2 * Vparticle, volume remains unaltered!


voidfractionModel bigParticle;
    maxCellsPerParticle 1000;
    alphaMin 0.10;
    weight 1.;
    porosity 5.0;


The bigParticle voidFraction model is supposed to be used when a particle (or its representation) is bigger than a CFD cell. The voidfraction field is set in those cell whose centres are inside the particle which results in a stairstep representation of the bodies within the mesh (i.e. voidfraction is either 1 (fluid) of zero (solid)). For archiving accurate results, approx. 8 cells per particle diameter are necessary.

The region of influence of a particle can be increased artificially by “porosity”, which blows up the particles, but keeps their volume (for voidfraction calculation) constant.

The particle volume occupied in the CFD domain can be adjusted by the parameter “weight”, using Vparticle=dsphere^3*pi/6*weight.

Parts of this sub-model contributed by Alice Hager, JKU.