# src/two-phase-levelset.h

# Two-phase interfacial flows with levelset

This file helps setup simulations for flows of two fluids separated by an interface (i.e.Â immiscible fluids). It is typically used in combination with a Navierâ€“Stokes solver.

The interface between the fluids is tracked with a levelset method. The signed distance to the interface is tracked by `d`

. The volume fraction field `f`

is computed from the signed distance.

Note that the coupled VOF and levelset solver should be prefered as it ensures much better mass conservation.

This solver can be combined with the integral formulation of surface tension.

The volume fraction in fluid 1 is f=1 and f=0 in fluid 2. The densities and dynamic viscosities for fluid 1 and 2 are *rho1*, *mu1*, *rho2*, *mu2*, respectively.

```
#include "tracer.h"
scalar d[], f[], * tracers = {d};
#include "two-phase-generic.h"
void levelset_to_vof (scalar d, scalar f)
{
vertex scalar phi[];
foreach_vertex()
phi[] = (d[] + d[-1] + d[0,-1] + d[-1,-1])/4.;
fractions (phi, f);
}
```

The initial volume fraction is computed from the initial distance field, which must be initialised by the user.

```
event init (i = 0)
{
levelset_to_vof (d, f);
}
```

The distance function is reinitialised at each timestep.

```
#include "redistance.h"
event properties (i++)
{
redistance (d, imax = 3);
levelset_to_vof (d, f);
}
```