Defining the domain¶

All simulations, whether using an embedded boundary (EB) or not, are specified on a simple cuboid domain. The low and high corners of the cuboid are defined by the prob_lo and prob_hi inputs.

The following inputs are defined using the prefix geometry:

	Description	Type	Default
coord_sys	Coordinate system used in simulation. Only Cartesian coordinates (`coord_sys = 0`) are supported.	Int	0
prob_lo	Low corner of physical domain (physical not index space)	Reals<3>	None
prob_hi	High corner of physical domain (physical not index space)	Reals<3>	None

Attention

MFIX-Exa geometry restrictions:

There is no support for 1D or 2D simulation domains.
Cartesian is the only supported coordinate system.

Mesh¶

The following inputs are defined using the prefix amr:

	Description	Type	Default
n_cell	Number of cells at level 0 in each coordinate direction. Must be divisible by `amr.blocking_factor` in each dimension.	Ints<3>	None

The base mesh spacing is computed for each direction by dividing the domain length by the number of cells. The mesh spacing is required to be the same in all directions:

\[\frac{\mathtt{prob\_hi[0]} - \mathtt{prob\_lo[0]}}{\mathtt{n\_cell[0]}} = \frac{\mathtt{prob\_hi[1]} - \mathtt{prob\_lo[1]}}{\mathtt{n\_cell[1]}} = \frac{\mathtt{prob\_hi[2]} - \mathtt{prob\_lo[2]}}{\mathtt{n\_cell[2]}}\]

The inputs for defining the mesh for a single-level simulation are demonstrated in the following example and illustrated in Fig. 1. In this example, the domain is a \(4 \times 1 \times 1\) cuboid, and there are \(32 \times 8 \times 8\) cells in the X, Y, and Z directions, respectively. The result is a uniform mesh spacing of \(0.125\) m in all three directions.

Listing 1 Snippet of inputs for mesh example. This is not a complete input file.¶

# Define periodicity and domain extents
# -------------------------------------------------------------
geometry.coord_sys   =  0           # Cartesian coordinates
geometry.is_periodic =  0   0   0   # periodicity for each direction
geometry.prob_lo     =  0.  0.  0.  # lo corner of physical domain.
geometry.prob_hi     =  4.  1.  1.  # hi corner of physical domain

# Define the maximum level of refinement and number of cells
# -------------------------------------------------------------
amr.n_cell = 32  8  8

domain used with box embedded boundary — Fig. 1 Example of a single-level mesh.¶

Warning

MFIX-Exa simulations with a non-uniform mesh will not run.

Grid settings¶

The following inputs are defined using the prefix amr:

	Description	Type	Default
max_grid_size_x	Maximum number of cells in each grid in X. Can be specified per-level.	Ints	32
max_grid_size_y	Maximum number of cells in each grid in Y. Can be specified per-level.	Ints	32
max_grid_size_z	Maximum number of cells in each grid in Z. Can be specified per-level.	Ints	32
blocking_factor_x	Each grid in X must be divisible by `blocking_factor_x`. Can be specified per-level.	Ints	8
blocking_factor_y	Each grid in Y must be divisible by `blocking_factor_y`. Can be specified per-level.	Ints	8
blocking_factor_z	Each grid in Z must be divisible by `blocking_factor_z`. Can be specified per-level.	Ints	8

Note, the default for max_grid_size is 64 for GPU runs.

The domain is decomposed into grids by dividing the number of cells by the max grid size for each direction (e.g., n_cells[0]/max_grid_size_x). The blocking factor ensures that the grids will be sufficiently coarsenable for good multigrid performance; therefore, the max_grid_size must be divisible by the corresponding blocking_factor.

Note

The AMReX documentation contains a significant amount of information on grid creation and load balancing. Users are strongly encouraged to read the relevant sections.

Periodic domains¶

The following inputs are defined using the prefix geometry:

	Description	Type	Default
is_periodic	1 for true, 0 for false (one value for each coordinate direction)	Ints<3>	0 0 0

Pressure drop¶

The following inputs are defined using the prefix mfix:

	Description	Type	Default
delp_dir	Direction for specified pressure drop. The domain must be periodic in the the specified direction. Options: `0`: X `1`: Y `2`: Z	Int	None
delp	Pressure drop (Pa)	Real	0

Description

Type

Default

delp_dir

Direction for specified pressure drop. The domain must be periodic in the the specified direction.

Options:

0: X
1: Y
2: Z

Int

None

delp

Pressure drop (Pa)

Real

Reference frame¶

MFIX‑Exa supports simulations in either an inertial (laboratory) reference frame or a uniformly rotating reference frame. The choice of reference frame affects how momentum equations are solved and whether additional pseudo‑forces (Coriolis and centrifugal) are included in the fluid and solids momentum balances.

The following inputs are defined using the prefix mfix:

	Description	Type	Default
reference_frame	Specifies the reference frame in which the governing equations are evaluated. Options: `inertial`: A static (laboratory) reference frame. `rotating`: A uniformly rotating frame.	String	inertial

Description

Type

Default

reference_frame

Specifies the reference frame in which the governing equations are evaluated.

Options:

inertial: A static (laboratory) reference frame.
rotating: A uniformly rotating frame.

String

inertial

The following inputs are defined using the prefix reference_frame:

	Description	Type	Default
axis	The direction of the rotation axis in physical space.	Reals<3>	None
axis_point	The location through which the rotation axis passes.	Reals<3>	None
angular_speed	Scalar angular speed of the rotating frame, in radians per second.	Real	None