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Add optional dissipation for Div_par_mod in Fci #3467

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Merged
dschwoerer merged 3 commits into from
Aug 24, 2026
Merged

Add optional dissipation for Div_par_mod in Fci #3467

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bb63ea4
Added dissipative flag to Div_par_mod in Fci
totork Aug 21, 2026
d204053
Formatting
totork Aug 21, 2026
d5f4814
Only check if dissipative is used in Div_par_mod in the non-Fci part
totork Aug 21, 2026
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4 changes: 2 additions & 2 deletions include/bout/fv_ops.hxx
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Original file line number Diff line number Diff line change
Expand Up @@ -156,8 +156,8 @@ Field3D Div_Perp_Lap(const Field3D& a, const Field3D& f, CELL_LOC outloc = CELL_
/// For FCI fields this diagnostic is currently set to zero.
template <typename CellEdges = MC>
Field3D Div_par_mod(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in, Field3D& flow_ylow,
bool fixflux = true);
const Field3D& wave_speed_in, Field3D& flow_ylow, bool fixflux = true,
bool dissipative = false);

/// This operator calculates Div_par(f v v)
/// It is used primarily (only?) in the parallel momentum equation.
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17 changes: 16 additions & 1 deletion include/bout/fv_ops_impl.hxx
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Expand Up @@ -633,7 +633,8 @@ Field3D Div_f_v(const Field3D& n_in, const Vector3D& v, bool bndry_flux) {
/// Already includes area factor * flux
template <typename CellEdges>
Field3D Div_par_mod(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in, Field3D& flow_ylow, bool fixflux) {
const Field3D& wave_speed_in, Field3D& flow_ylow, bool fixflux,
bool dissipative) {

Coordinates* coord = f_in.getCoordinates();
ASSERT1_FIELDS_COMPATIBLE(f_in, v_in);
Expand Down Expand Up @@ -661,11 +662,25 @@ Field3D Div_par_mod(const Field3D& f_in, const Field3D& v_in,
- 0.25 * (f_in[i] + f_down[iym]) * (v_in[i] + v_down[iym])
* coord->cell_area_ylow()[i])
/ coord->cell_volume()[i];

if (dissipative) {
const BoutReal amax = BOUTMAX(fabs(wave_speed_in[i]), fabs(v_in[i]),
fabs(v_up[iyp]), fabs(v_down[iym]));
result[i] += (0.5 * amax * (f_in[i] - f_up[iyp]) * coord->cell_area_yhigh()[i]
+ 0.5 * amax * (f_in[i] - f_down[iym]) * coord->cell_area_ylow()[i])
/ coord->cell_volume()[i];
}
}
return result;
}
ASSERT1_FIELDS_COMPATIBLE(f_in, wave_speed_in);

// Throw error when not Fci
if (dissipative) {
throw BoutException("Using dissipative flag in Div_par_mod but no Fci parallel "
"transform. This flag will have no impact on the simulation");
}

const Mesh* mesh = f_in.getMesh();

CellEdges cellboundary;
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5 changes: 3 additions & 2 deletions manual/sphinx/user_docs/differential_operators.rst
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Expand Up @@ -586,13 +586,14 @@ than ``FV::Div_par`` for the same limiter choice.
template<typename CellEdges = MC>
Field3D Div_par_mod(const Field3D &f_in, const Field3D &v_in,
const Field3D &a, Field3D &flow_ylow,
bool fixflux=true);
bool fixflux=true, bool dissipative=false);


The extra output argument ``flow_ylow`` stores the flow through the lower
:math:`y` cell boundary, including the area factor. This can be useful as a
diagnostic in energy or flux budgets. For FCI fields this diagnostic is
currently returned as zero.
currently returned as zero. The flag ``dissipative`` activates a local
Rusanov-flux if used in Fci.


Parallel momentum flux ``Div_par_fvv``
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14 changes: 7 additions & 7 deletions src/mesh/fv_ops.cxx
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Expand Up @@ -578,7 +578,7 @@ template Field3D Div_par<Upwind>(const Field3D& f_in, const Field3D& v_in,
template Field3D Div_f_v<Upwind>(const Field3D& n_in, const Vector3D& v, bool bndry_flux);
template Field3D Div_par_mod<Upwind>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in, Field3D& flow_ylow,
bool fixflux);
bool fixflux, bool dissipative);
template Field3D Div_par_fvv_heating<Upwind>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in,
Field3D& flow_ylow, bool fixflux);
Expand All @@ -592,7 +592,7 @@ template Field3D Div_par<Fromm>(const Field3D& f_in, const Field3D& v_in,
template Field3D Div_f_v<Fromm>(const Field3D& n_in, const Vector3D& v, bool bndry_flux);
template Field3D Div_par_mod<Fromm>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in, Field3D& flow_ylow,
bool fixflux);
bool fixflux, bool dissipative);
template Field3D Div_par_fvv_heating<Fromm>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in,
Field3D& flow_ylow, bool fixflux);
Expand All @@ -606,7 +606,7 @@ template Field3D Div_par<MinMod>(const Field3D& f_in, const Field3D& v_in,
template Field3D Div_f_v<MinMod>(const Field3D& n_in, const Vector3D& v, bool bndry_flux);
template Field3D Div_par_mod<MinMod>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in, Field3D& flow_ylow,
bool fixflux);
bool fixflux, bool dissipative);
template Field3D Div_par_fvv_heating<MinMod>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in,
Field3D& flow_ylow, bool fixflux);
Expand All @@ -620,7 +620,7 @@ template Field3D Div_par<MC>(const Field3D& f_in, const Field3D& v_in,
template Field3D Div_f_v<MC>(const Field3D& n_in, const Vector3D& v, bool bndry_flux);
template Field3D Div_par_mod<MC>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in, Field3D& flow_ylow,
bool fixflux);
bool fixflux, bool dissipative);
template Field3D Div_par_fvv_heating<MC>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in, Field3D& flow_ylow,
bool fixflux);
Expand All @@ -635,7 +635,7 @@ template Field3D Div_f_v<Superbee>(const Field3D& n_in, const Vector3D& v,
bool bndry_flux);
template Field3D Div_par_mod<Superbee>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in, Field3D& flow_ylow,
bool fixflux);
bool fixflux, bool dissipative);
template Field3D Div_par_fvv_heating<Superbee>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in,
Field3D& flow_ylow, bool fixflux);
Expand All @@ -650,7 +650,7 @@ template Field3D Div_f_v<VanAlbada>(const Field3D& n_in, const Vector3D& v,
bool bndry_flux);
template Field3D Div_par_mod<VanAlbada>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in, Field3D& flow_ylow,
bool fixflux);
bool fixflux, bool dissipative);
template Field3D Div_par_fvv_heating<VanAlbada>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in,
Field3D& flow_ylow, bool fixflux);
Expand All @@ -664,7 +664,7 @@ template Field3D Div_par<WENO3>(const Field3D& f_in, const Field3D& v_in,
template Field3D Div_f_v<WENO3>(const Field3D& n_in, const Vector3D& v, bool bndry_flux);
template Field3D Div_par_mod<WENO3>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in, Field3D& flow_ylow,
bool fixflux);
bool fixflux, bool dissipative);
template Field3D Div_par_fvv_heating<WENO3>(const Field3D& f_in, const Field3D& v_in,
const Field3D& wave_speed_in,
Field3D& flow_ylow, bool fixflux);
Expand Down
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