Data setting for the cavitation model

Introduction

The cavitation model is based on a homogeneous mixture model, and a sub-model of the Volume of Fluid model. The physical properties (density and dynamic viscosity) of the mixture depend on a resolved void fraction and constant reference properties of the liquid phase and the gas phase. The void fraction is given by an advection equation with a vaporization/condensation source/sink term. This term is modeled by the Merkle's model. The model also integrates the eddy-viscosity correction of Reboud.

Activation of the model

The module can be activated in cs_user_model in cs_user_parameters.c as show below:

  cs_vof_parameters_t *vof_param = cs_get_glob_vof_parameters();
  vof_param->vof_model = CS_VOF_ENABLED | CS_VOF_MERKLE_MASS_TRANSFER;

Data structure is defined in VOF model for free surface flow or dispersed flow, Mixture properties and Cavitation model. Cavitation modelling main feature consists in modelling vaporisation/condensation with Merkle model providing source / sink term for the void fraction equation.

Cavitation module specific parameters.

When cavitation model is enabled, specific input parameters can be set in cs_user_parameters in cs_user_parameters.c file as shown below:

Homogeneous mixture physical properties

The reference density, in , and molecular viscosity, , of the liquid phase and the gas phase should be set. For instance:

 
  cs_vof_parameters_t *vof_param = cs_get_glob_vof_parameters();
 
  /* Reference density, in kg/m3, and molecular viscosity, kg/(m s), of the
     liquid phase */
 
  vof_param->rho1 = 1.e3;
  vof_param->mu1 = 1.e-3;
 
  /* Reference density, in kg/m3, and molecular viscosity, kg/(m s), of the
     gas phase */
 
  vof_param->rho2 = 1.;
  vof_param->mu2 = 1.e-5;
 

Other parameters, specific to cavitation are stored in cs_cavitation_parameters_t structure. A pointer to this structure should be retrieved as follows:

 
  cs_cavitation_parameters_t *cavit_param =
    cs_get_glob_cavitation_parameters();
 

Model parameters of the vaporization term (Merkle model)

Merkle's model parameters should be set. Merkle's model is based on a barotropic law for the density (see cavitation.f90). In that way, its principal parameter is the saturation pressure of the fluid, in . For instance, the saturation pressure of the water at twenty celcius degrees is set below:

  cavit_param->presat = 2.e3;

Merkle's model also requires a reference length scale and velocity of the flow. For instance:

  cavit_param->linf = 0.1;
  cavit_param->uinf = 1.;

These scales are integral scales. For instance, considering the cavitating flow across a foil in a duct, the reference velocity should be the bulk velocity and the reference length scale should be the chord of the foil.

Interaction with turbulence

The mixture eddy-viscosity correction proposed by Reboud can be accounted for as shown below:

  cavit_param->icvevm = 1;

Using an eddy-viscosity model (see turbulence options), this option is recommended and is hence a default setting. Of course, this option has no effect for second moment closure or large eddy simulations. Note that the coefficent mcav of the reboud correction (see cavitation.f90) can also be adjusted in the cs_user_parameters function.

Numerical options

Advanced numerical parameters may also be set in this function, if necessary. The concerned variables are listed in Numerical parameters.