4.22. Turbulence Damping

In multiphase flows, a high velocity gradient at the interface between two fluids results in high turbulence generation, in both phases. Hence, turbulence damping is required in the interfacial area to model such flows correctly.

Important: Turbulence damping is available only with the - and -ε models.

For the - model, the following source term is added to the -equation [161]:

(4–443)

where
	= Interfacial area density for phase
	= Cell height normal to interface
	= - model closure coefficient of destruction term, which is equal to 0.075
	= Damping factor
	= Viscosity of phase
	= Density of phase

For the -ε model, the following source term is added to the ε-equation:

(4–444)

where
	= turbulent kinetic energy of phase
	= model constant equal to 0.09 (see Model Constants)

The interfacial area density for phase is calculated as

(4–445)

where
	= Volume fraction of phase
	= Magnitude of gradient of volume fraction

The grid size is calculated internally using grid information. You can specify the damping factor in the Viscous Model dialog box. The default value for the damping factor is 10.

Turbulence damping is available with the VOF and Mixture models. Note that it is also available with the Eulerian multiphase model when using the multi-fluid VOF model. To use this option, refer to Turbulence Damping.

If the Eulerian multiphase model is enabled, you can specify a turbulence multiphase model. If the Per Phase turbulence model is used, then the source term is added to the or ε equation of each phase. If the VOF or mixture model is enabled, or the Eulerian multiphase model is used with the Mixture turbulence model, the term is summed over all the phases and added as a source term to the mixture level or ε equation. For information about turbulence multiphase modeling, see Modeling Turbulence.