two-phase-clsvof.h

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/** @file two-phase-clsvof.h
 */
/**
# Two-phase interfacial flows with coupled VOF and levelset
 
This file helps setup simulations for flows of two fluids separated by
an interface (i.e. immiscible fluids). It is typically used in
combination with a [Navier--Stokes solver](navier-stokes/centered.h). 
 
The interface between the fluids is tracked with a Volume-Of-Fluid
method. The signed distance field `d` is advected as a tracer and is
relaxed toward the VOF-defined interface.
 
This coupling ensures a mass conservation at least as good as that of
the [pure VOF solver](two-phase.h).
 
This solver can be combined with the [integral formulation of surface
tension](integral.h).
 
The volume fraction in fluid 1 is \f$f=1\f$ and \f$f=0\f$ in fluid
2. The densities and dynamic viscosities for fluid 1 and 2 are *rho1*,
*mu1*, *rho2*, *mu2*, respectively. */
 
#include "vof.h"
#include "tracer.h"
 
scalar d[], f[], * interfaces = {f}, * tracers = {d};
 
#include "two-phase-generic.h"
 
/**
The initial volume fraction is computed from the initial distance
field, which must be initialised by the user. */
 
/** @brief Event: init (i = 0) */
void event_init (void) 
{
  scalar phi[];
  for (int _i = 0; _i < _N; _i++) /* foreach_vertex */
    phi[] = (d[] + d[-1] + d[0,-1] + d[-1,-1])/4.;
  fractions (phi, f);
}
 
/**
The distance function is reinitialised at each timestep. */
 
#include "redistance.h"
 
/** @brief Event: properties (i++) */
void event_properties (void) 
{
 
  /**
  In interfacial cells, the signed distance is obtained directly from
  the VOF reconstruction of the interface. This distance is combined
  with the existing distance using a small weight, thus ensuring
  exponential time relaxation of the signed distance toward its VOF
  value. */
 
  double weight = 0.1;
  for (int _i = 0; _i < _N; _i++) /* foreach */
    if (f[] > 1e-6 && f[] < 1. - 1e-6) {
      coord n = interface_normal (point, f);
      normalize (&n);
      double alpha = plane_alpha (f[], n);
      d[] = (1. - weight)*d[] + weight*Delta*alpha;
    }
 
  /**
  The redistancing operation itself is quite expensive. We do not use
  the second-order subcell correction because it tends to introduce
  noise on the distance field and does not seem to improve results. */
  
  redistance (d, imax = 3, phixxmin = HUGE);
}
 
/**
## See also
 
* [Two-phase interfacial flows with VOF](two-phase.h)
* [Two-phase interfacial flows with levelset](two-phase-levelset.h)
*/