Plotfiles and other output¶

The following inputs must be preceded by the prefix output.plot and control frequency and naming of plotfile generation. (mfix.file_digits sets the number of digits used in plotfile and checkpoint names.)

	Description	Type	Default
format	Plot file format. Options: `amrex` - native AMReX plotfiles `hdf5` - AMReX HDF5 plotfiles (requires building the solver with HDF5 support).	String	amrex
file	Prefix to use for plotfile output.	String	plt
int	Plotting interval in timesteps (0 to disable).	Int	0
per_approx	Approximate plotting interval in simulation time (does not modify dt). 0 to disable. Only one of `int` or `per_approx` may be specified.	Real	0
on_restart	Write a plotfile when restarting (only used if `int`>0).	Bool	false

HDF5 compression¶

For HDF5 output, Eulerian plot data is written to [file][step].h5, and particle data is written under the corresponding [file][step] directory. When no Eulerian variables are selected, MFIX-Exa still writes a zero-component HDF5 plotfile root so grid and geometry metadata is available beside particle output.

The following inputs must be preceded by the prefix output.hdf5:

	Description	Type	Default
compression	HDF5 compression. By default, no compression is used in writing HDF5 plotfiles. AMReX supports ZLIB, SZ and ZFP data compression of HDF5 datasets; SZ and ZFP require additional libraries. See AMReX documentation for additional information.	String	None@0

Selecting plotfile variables¶

The contents of a plotfile are chosen by name. The following inputs must be preceded by the prefix output.plot:

	Description	Type	Default
fluid.variables	Fluid (Eulerian) variables to write to the plotfile.	Strings	None
particles.variables	Particle (Lagrangian) variables to write to the plotfile.	Strings	None

Neither list has a default: a plotfile contains what the inputs ask for and nothing else. Omitting fluid.variables writes a plotfile with no fluid components – the header-only form already used by particle-only runs – and omitting particles.variables writes a plotfile with no particle data. Setting a write frequency (int or per_approx) while leaving both lists empty is reported as an error at start-up, since it asks for plotfiles with nothing in them.

The fluid names below are also used by the in-situ backends – output.ascent.fluid.variables and output.catalyst.fluid.variables – so a fluid field is spelled the same way wherever it is requested.

Both accept an ordered list of names; the plotfile components appear in the order requested. For example:

output.plot.fluid.variables = velocity pressure temperature species
output.plot.particles.variables = radius velocity temperature

Fluid variables¶

The names below may be used in output.plot.fluid.variables. The same names are accepted by monitors, reports and the in-situ visualization backends, so a field is spelled the same way wherever it is requested.

Name	Plotfile components
velocity	Fluid velocity: `u_g`, `v_g`, `w_g`
pressure	Perturbation pressure: `p_g`
pressure_gradient	Pressure gradient: `gpx`, `gpy`, `gpz`
density	Fluid density: `ro_g`
volume_fraction	Fluid phase volume fraction: `ep_g`
temperature	Fluid temperature: `T_g`
enthalpy	Fluid mixture enthalpy: `h_g`
specific_heat	Fluid mixture specific heat: `cp_g`
conductivity	Fluid thermal conductivity: `k_g`
viscosity	Fluid molecular viscosity: `mu_g`
molecular_weight	Fluid mixture molecular weight: `MW_g`
tracer	Fluid tracer: `trac`
vorticity	Fluid vorticity: `vort`
species	Fluid species mass fraction: `X_[species]_g`
species_diffusivity	Fluid species diffusion coefficients: `D_[species]_g`
species_specific_heat	Fluid species specific heats: `cp_[species]_g`
species_enthalpy	Fluid species enthalpies: `h_[species]_g`
transfer	Fluild-particle transfer source terms. * drag force: `beta`, `drag_x`, `drag_y`, `drag_z` * convective heat transfer: `gamma`, `gammaTp` * virtual mass force: `vm_coeff`
chem_transfer	Chemistry transfer source terms. * mass transfer: `chem_ro_txfr_[species]` * enthalpy transfer: `chem_h_txfr`
eb_volume_fraction	Geometric volume fraction: `volfrac`
eb_drag	Drag force computed on EB surface: `eb_drag_x`, `eb_drag_y`, `eb_drag_z`
eb_temperature	EB temperature: `T_eb`
incident_radiation	Incident radiation field: `rte_G`
mac_phi	MAC projection scalar: `mac_phi`
rank	Grids with MPI rank: `proc`
particle_rank	Grids with MPI rank for particles: `proc_p`

A single component of a vector or a single species may be requested by appending it to the name, so velocity.x writes only u_g, species.H2O writes only X_H2O_g, and transfer.beta writes only the drag coefficient. The component spellings used by monitors – vel_g_x, gp_x, X_gk_[species], txfr_beta and similar – are accepted here as well.

Particle variables¶

The names below may be used in output.plot.particles.variables.

Name	Plotfile components
radius	Particle radius: `radius`
density	Particle density: `ro_p`
velocity	Particle velocity: `velx`, `vely`, `velz`
angular_velocity	Particle angular velocity: `omegax`, `omegay`, `omegaz` (DEM only)
grad_tau	Particle stress gradient: `grad_tau_x`, `grad_tau_y`, `grad_tau_z` (PIC only)
statwt	Parcel statistical weight: `statwt`
drag_coefficient	Fluid-particle drag coefficient: `dragcoeff`
drag_source	Fluid-particle drag force: `dragx`, `dragy`, `dragz`
temperature	Particle temperature: `temperature`
phase	Particle type index: `phase`
state	Particle state: `state`
species	Particle species mass fractions: `X_[species]`
volume_fraction	Phase volume fraction at parcel: `ep_s` (PIC only)
virtual_mass_coefficient	Virtual mass coefficient: `vm_coeff`
acceleration	Acceleration force: `acc_x`, `acc_y`, `acc_z`
pft_neighbor	Particle tangential contact history force: `PFT_NEIGHBOR_[n]`
pft_neighbor_flags	Particle tangential contact history flags: `PFT_NEIGHBOR_FLAG_[n]`

Requesting a variable that the current setup does not provide is an error reported at start-up: asking for temperature without solving fluid enthalpy, for instance, or for a species that is not defined.

Note

The older mfix.plt_* flags (mfix.plt_vel_g, mfix.plt_T_g and so on) still work and are converted to the equivalent variables entry, but they are deprecated and should not be used in new inputs.

Note

Per-region solids plotfiles (mfix.solids.regions and the [region_name] keys under it) were removed in September 2026. A run whose inputs still set them stops at start-up with a message pointing here. Plotfiles now always cover the whole domain; use the variable lists above to choose their contents. Writing plotfiles over sub-domains may return as a separate feature.

Debugging¶

The following inputs control whether particle data should be written out in ASCII format. They must be preceded by the prefix output.particle_ascii.

	Description	Type	Default
file	Prefix to use for ASCII particle output file name.	String	par
int	ASCII particle output interval in timesteps. 0 to disable.	Int	0
per_approx	Approximate simulation time period for ASCII particle output. 0 to disable. Only one of `int` or `per_approx` may be specified.	Real	0

The following inputs control whether the EB geometry or level set should be written. They must be preceded by the prefix output.plot. (Writing the EB surface in VTP format is controlled separately by mfix.write_eb_surface.)

	Description	Type	Default
write_ls	Write a plotfile containing the level set and volume fraction. If enabled, it will only be written once, after initialization or restart.	Bool	false
write_geom	Write a plotfile containing the EB geometry data. If true, it will only be written once, after initialization or restart.	Bool	false

They must be preceded by the prefix mfix.

	Description	Type	Default
plt_regtest	Flag to enable variables stored for CCSE regression testing.	Int	0

Ascent has been integrated into MFIX-Exa for in situ visualization. See Ascent for details.