NAME
Diffuse_visc
SYNOPSIS
call Diffuse_visc (integer(IN) :: sweepDir,
integer(IN) :: igeom,
integer(IN) :: blockID,
integer(IN) :: numCells,
integer(IN) :: blkLimits(2,MDIM),
integer(IN) :: blkLimitsGC(2,MDIM),
real(IN) :: leftCoords(MAXCELLS or numCells),
real(IN) :: rightCoords(MAXCELLS or numCells),
real(INOUT) :: temp_flx(NFLUXES,:,:,:),
real(IN) :: areaLeft(:,:,:),
real(IN) :: secondCoord(MAXCELLS or numCells),
real(IN) :: thirdCoord(MAXCELLS or numCells))
DESCRIPTION
Diffuse_visc alters the velocity fluxes for a block to account for viscosity.
Energy fluxes (for E_FLUX and, if defined, EINT_FLUX) are also adjusted
accordingly.
This is an explicit method, so a timestep limiter will be required.
Stability is guaranteed for
dx**2
dt < .5* -------
nu
Fluxes in PPM are stored at the zone boundaries, the temperature, etc. are
at the zone centers. So the velocity fluxes (more exactly, momentum fluxes)
acquire terms like F = -nu * grad(v), which is approximated as
nu_i + nu_{i-1} v(xyz)_i - v(xyz)_{i-1}
F(xyz)_i = - ----------------- * ------------------------ .
2 dx
This routine computes the velocity and energy fluxes from
viscosity and adds them to the corresponding fluxes returned from
hydro_1d. It is to be called after calling hydro_1d on a block.
The updated energy fluxes are then used in hy_ppm_updateSoln to
produce the updated velocities and energy.
ARGUMENTS
sweepDir - the current sweep direction igeom - the geometry flag for the current sweep direction blockID - the block number to operate on numCells - the number of Cells along the sweep direction leftCoords - Coordinates of the left edge of the zones rightCoords - Coordinates of the right edge of the zones temp_flx - Temporary storage for fluxes along sweep direction areaLeft - Cell face areas at the left (smaller) cell side secondCoord - for an x sweep: y coordinate; for a y sweep: x coord; for a z sweep: x coord thirdCoord - for an x sweep: z coordinate; for a y sweep: z coord; for a z sweep: y coord blkLimits - endpoints of block indices without including gcells blkLimitsGC - endpoints of block indices including gcells
NOTES
This routine is used by the PPM implementation of the Hydro unit.
Other implementations of Hydro, in particular MHD and RHD, may have their
own mechanisms for handling diffusive effects that bypass Diffuse_visc
(and the Diffuse code unit in general), or they may lack support for
diffusive effects.
SEE ALSO
Diffuse_therm
HISTORY
Apparently this subroutine used to be called visc_explicit. Visc_explicit started out as a very lightly modified version of therm_explicit.