12.1.10. Boundary Conditions¶

Boundary conditions (BC) are specified over flow planes or 2D surfaces that are normal to one of the coordinate directions and coincide with a face of the scalar control-volume. The values for one of the three pairs of coordinates are equal. The surface is defined by the constant coordinates of each of the four edges, which can be specified with physical coordinates or cell indices, and the two equal values for the direction normal to the face, which can only be specified with physical coordinates. If cell sizes are not small enough to resolve a surface specified using physical coordinates, MFIX will indicate this problem with an error message.

A flow plane must have a wall cell (or an outside boundary) on one side and a flow cell on the other side. The BC section is also used to specify obstacles in the flow domain. Obstacles are 3D regions, just as for the IC regions: X_w X_e, Y_s Y_n, and Z_t Z_b. By default the outside boundary is initialized as no-slip walls. For cylindrical coordinates the axis is initialized as a free-slip wall.

Two boundary surfaces must not intersect. Two obstacle regions may intersect.

12.1.10.1. BC_DEFAULT_WALLS¶

Data Type: LOGICAL

Apply default wall Boundary conditions along the MFIX box: (no-slip, adiabatic walls).

12.1.10.2. BC_X_W(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

X coordinate of the west face or edge.

12.1.10.3. BC_X_E(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

X coordinate of the east face or edge.

12.1.10.4. BC_Y_S(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Y coordinate of the south face or edge.

12.1.10.5. BC_Y_N(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Y coordinate of the north face or edge.

12.1.10.6. BC_Z_B(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Z coordinate of the bottom face or edge.

12.1.10.7. BC_Z_T(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Z coordinate of the top face or edge.

12.1.10.8. BC_I_W(BC)¶

Data Type: INTEGER

$1 \leq B C \leq 500$

I index of the west-most cell.

12.1.10.9. BC_I_E(BC)¶

Data Type: INTEGER

$1 \leq B C \leq 500$

I index of the east-most cell.

12.1.10.10. BC_J_S(BC)¶

Data Type: INTEGER

$1 \leq B C \leq 500$

J index of the south-most cell.

12.1.10.11. BC_J_N(BC)¶

Data Type: INTEGER

$1 \leq B C \leq 500$

J index of the north-most cell.

12.1.10.12. BC_K_B(BC)¶

Data Type: INTEGER

$1 \leq B C \leq 500$

K index of the bottom-most cell.

12.1.10.13. BC_K_T(BC)¶

Data Type: INTEGER

$1 \leq B C \leq 500$

K index of the top-most cell.

12.1.10.14. BC_TYPE(BC)¶

Data Type: CHARACTER

$1 \leq B C \leq 500$

Type of boundary.

Table 12.60 Valid Values¶
Name	Default?	Description
`DUMMY`		The specified boundary condition is ignored. This is useful for turning off some boundary conditions without having to delete them from the file.
`MASS_INFLOW`		Mass inflow rates for gas and solids phases are specified at the boundary.
`MASS_OUTFLOW`		The specified values of gas and solids mass outflow rates at the boundary are maintained, approximately. This condition should be used sparingly for minor outflows, when the bulk of the outflow is occurring through other constant pressure outflow boundaries.
`P_INFLOW`		Inflow from a boundary at a specified constant pressure. To specify as the west, south, or bottom end of the computational region, add a layer of wall cells to the west, south, or bottom of the PI cells. Users need to specify all scalar quantities and velocity components. The specified values of fluid and solids velocities are only used initially as MFIX computes these values at this inlet boundary.
`P_OUTFLOW`		Outflow to a boundary at a specified constant pressure. To specify as the west, south, or bottom end of the computational region, add a layer of wall cells to the west, south, or bottom of the PO cells.
`FREE_SLIP_WALL`		Velocity gradients at the wall vanish. If BC_JJ_PS is equal to 1, the Johnson-Jackson boundary condition is used for solids. A FSW is equivalent to using a PSW with Hw=0.
`NO_SLIP_WALL`		All components of the velocity vanish at the wall. If BC_JJ_PS is equal to 1, the Johnson-Jackson boundary condition is used for solids. A NSW is equivalent to using a PSW with vw=0 and Hw undefined.
`PAR_SLIP_WALL`		Partial slip at the wall implemented as the boundary condition: dv/dn + Hw (v - vw) = 0, where n is the normal pointing from the fluid into the wall. The coefficients Hw and vw should be specified. For free-slip set Hw = 0. For no-slip leave Hw undefined (Hw=+inf) and set vw = 0. To set Hw = +inf, leave it unspecified. If BC_JJ_PS is equal to 1, the Johnson-Jackson boundary condition is used for solids.

12.1.10.15. BC_PSD_TYPE(BC, PHASE)¶

Data Type: CHARACTER

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Particle size distribution type of solids phase at BC region.

Table 12.61 Valid Values¶
Name	Default?	Description
`MONO`	◉	Uniform particle size.
`NORMAL`		Normal (Gaussian) particle size distribution.
`LOG_NORMAL`		Log-normal particle size distribution.
`CUSTOM`		Particle size distribution specified in external file.

12.1.10.16. BC_PSD_MEAN_DP(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Mean value of particle size distribution of solids phase in the BC region. For a log-normal psd, The mean diameter (µ) and standard deviation (𝜎) will be used to compute the log-normal parameters µ_ln and 𝜎_ln : µ_ln = ln(µ²/√(µ² + 𝜎²)) and 𝜎_ln = √(ln(1 + (𝜎/µ)²)))

12.1.10.17. BC_PSD_STDEV(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Standard deviation of particle size distribution of solids phase in the BC region. For a log-normal psd, The mean diameter (µ) and standard deviation (𝜎) will be used to compute the log-normal parameters µ_ln and 𝜎_ln : µ_ln = ln(µ²/√(µ² + 𝜎²)) and 𝜎_ln = √(ln(1 + (𝜎/µ)²)))

12.1.10.18. BC_PSD_MAX_DP(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Maximum particle size of particle size distribution of solids phase in the BC region.

12.1.10.19. BC_PSD_MIN_DP(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Minimum particle size of particle size distribution of solids phase in the BC region.

12.1.10.20. BC_MI_START_TIME(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Mass inlet starting time (sec.). This controls DEM solids only (fluid flow starts at t=0).

12.1.10.21. BC_MI_END_TIME(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Mass inlet ending time (sec.). This controls DEM solids only (fluid flow starts at t=0).

12.1.10.22. BC_HW_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Gas phase Hw for partial slip boundary.

12.1.10.23. BC_HW_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Solids phase Hw for partial slip boundary.

12.1.10.24. BC_UW_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Gas phase Uw for partial slip boundary.

12.1.10.25. BC_UW_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Solids phase Uw for partial slip boundary.

12.1.10.26. BC_VW_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Gas phase Vw for partial slip boundary.

12.1.10.27. BC_VW_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Solids phase Vw for partial slip boundary.

12.1.10.28. BC_WW_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Gas phase Ww for partial slip boundary.

12.1.10.29. BC_WW_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Solids phase Ww for partial slip boundary.

12.1.10.30. BC_JJ_PS(BC)¶

Data Type: INTEGER

$1 \leq B C \leq 500$

Johnson and Jackson partial slip BC.

Table 12.62 Valid Values¶
Name	Default?	Description
`0`		Do not use Johnson and Jackson partial slip bc. Default if granular energy transport equation is not solved.
`1`		Use Johnson and Jackson partial slip bc. Default if granular energy transport equation is solved.

12.1.10.31. BC_JJ_M¶

Data Type: LOGICAL

Use a modified version of Johnson and Jackson: partial slip BC (BC_JJ_PS BC) with a variable specularity coefficient.

12.1.10.32. BC_THETAW_M(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Specified wall value, THETAw_M, in diffusion boundary condition: d(THETA_M)/dn + Hw (THETA_M - THETAw_M) = C, where n is the fluid-to-wall normal.

12.1.10.33. BC_HW_THETA_M(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Transfer coefficient, Hw, in diffusion boundary condition: d(THETA_M)/dn + Hw (THETA_M - THETAw_M) = C, where n is the fluid-to-wall normal.

12.1.10.34. BC_C_THETA_M(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Specified constant flux, C, in diffusion boundary condition: d(THETA_M)/dn + Hw (THETA_M - THETAw_M) = C, where n is the fluid-to-wall normal.

12.1.10.35. BC_HW_T_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Gas phase heat transfer coefficient, Hw, in diffusion boundary condition: d(T_g)/dn + Hw (T_g - T_ref) = C, where n is the fluid-to-wall normal.

12.1.10.36. BC_TW_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Specified gas phase wall temperature, when using constant temperature wall, or free stream gas reference temperature T_ref, in diffusion boundary condition: d(T_g)/dn + Hw (T_g - T_ref) = C, where n is the fluid-to-wall normal.

12.1.10.37. BC_C_T_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Specified constant gas phase heat flux, C, in diffusion boundary condition: d(T_g)/dn + Hw (T_g - T_ref) = C, where n is the fluid-to-wall normal.

12.1.10.38. BC_HW_T_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Solids phase heat transfer coefficient, Hw, in diffusion boundary condition: d(T_s)/dn + Hw (T_s - T_ref) = C, where n is the fluid-to-wall normal.

12.1.10.39. BC_TW_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Specified constant solids phase wall temperature, when using constant temperature wall, or free stream solids reference temperature T_ref, in diffusion boundary condition: d(T_s)/dn + Hw (T_s - T_ref) = C, where n is the fluid-to-wall normal.

12.1.10.40. BC_C_T_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Specified constant solids phase heat flux, C, in diffusion boundary condition: d(T_s)/dn + Hw (T_s - T_ref) = C, where n is the fluid-to-wall normal.

12.1.10.41. BC_HW_X_G(BC, SPECIES)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq S p e c i e s \leq 100$

Gas phase species mass transfer coefficient, Hw, in diffusion boundary condition: d(X_g)/dn + Hw (X_g - Xw_g) = C, where n is the fluid-to-wall normal.

12.1.10.42. BC_XW_G(BC, SPECIES)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq S p e c i e s \leq 100$

Specified wall gas species mass fraction, Xw, in diffusion boundary condition: d(X_g)/dn + Hw (X_g - Xw_g) = C, where n is the fluid-to-wall normal.

12.1.10.43. BC_C_X_G(BC, SPECIES)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq S p e c i e s \leq 100$

Specified constant gas species mass flux, C, in diffusion boundary condition: d(X_g)/dn + Hw (X_g - Xw_g) = C, where n is the fluid-to-wall normal.

12.1.10.44. BC_HW_X_S(BC, PHASE, SPECIES)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$
$1 \leq S p e c i e s \leq 100$

Solid phase species mass transfer coefficient, Hw, in diffusion boundary condition: d(X_s)/dn + Hw (X_s - Xw_s) = C, where n is the fluid-to-wall normal.

12.1.10.45. BC_XW_S(BC, PHASE, SPECIES)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$
$1 \leq S p e c i e s \leq 100$

Specified solids species mass fraction at the wall, Xw_s, in diffusion boundary condition: d(X_s)/dn + Hw (X_s - Xw_s) = C, where n is the fluid-to-wall normal.

12.1.10.46. BC_C_X_S(BC, PHASE, SPECIES)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$
$1 \leq S p e c i e s \leq 100$

Specified constant solids species mass flux, C, in diffusion boundary condition: d(X_s)/dn + Hw (X_s - Xw_s) = C, where n is the fluid-to-wall normal.

12.1.10.47. BC_HW_SCALAR(BC, SCALAR EQ.)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq S c a l a r E q . \leq 100$

Scalar transfer coefficient, Hw, in diffusion boundary condition: d(Scalar)/dn + Hw (Scalar - ScalarW) = C, where n is the fluid-to-wall normal.

12.1.10.48. BC_SCALARW(BC, SCALAR EQ.)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq S c a l a r E q . \leq 100$

Specified scalar value at the wall, ScalarW, in diffusion boundary condition: d(Scalar)/dn + Hw (Scalar - ScalarW) = C, where n is the fluid-to-wall normal.

12.1.10.49. BC_C_SCALAR(BC, SCALAR EQ.)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq S c a l a r E q . \leq 100$

Specified constant scalar flux, C, in diffusion boundary condition: d(Scalar)/dn + Hw (Scalar - ScalarW) = C, where n is the fluid-to-wall normal.

12.1.10.50. BC_EP_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Void fraction at the BC plane.

12.1.10.51. BC_P_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Gas pressure at the BC plane.

12.1.10.52. BC_ROP_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Bulk density of solids phase at the BC plane.

12.1.10.53. BC_EP_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Solids volume fraction at the BC plane.

12.1.10.54. BC_T_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Gas phase temperature at the BC plane.

12.1.10.55. BC_T_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Solids phase temperature at the BC plane.

12.1.10.56. BC_THETA_M(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Solids phase granular temperature at the BC plane.

12.1.10.57. BC_X_G(BC, SPECIES)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq S p e c i e s \leq 100$

Mass fraction of gas species at the BC plane.

12.1.10.58. BC_X_S(BC, PHASE, SPECIES)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$
$1 \leq S p e c i e s \leq 100$

Mass fraction of solids species at the BC plane.

12.1.10.59. BC_U_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

X-component of gas velocity at the BC plane.

12.1.10.60. BC_U_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

X-component of solids-phase velocity at the BC plane.

12.1.10.61. BC_V_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Y-component of gas velocity at the BC plane.

12.1.10.62. BC_V_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Y-component of solids-phase velocity at the BC plane.

12.1.10.63. BC_W_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Z-component of gas velocity at the BC plane.

12.1.10.64. BC_W_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Z-component of solids-phase velocity at the BC plane.

12.1.10.65. BC_VOLFLOW_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Gas volumetric flow rate through the boundary.

12.1.10.66. BC_VOLFLOW_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Solids volumetric flow rate through the boundary.

12.1.10.67. BC_MASSFLOW_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Gas mass flow rate through the boundary.

12.1.10.68. BC_MASSFLOW_S(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Solids mass flow rate through the boundary.

12.1.10.69. BC_DT_0(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

The interval at the beginning when the normal: velocity at the boundary is equal to BC_Jet_g0. When restarting run, this value and BC_Jet_g0 should be specified such that the transient jet continues correctly. MFIX does not store the jet conditions. For MASS_OUTFLOW boundary conditions, BC_DT_0 is the time period to average and print the outflow rates. The adjustment of velocities to get a specified mass or volumetric flow rate is based on the average outflow rate.

12.1.10.70. BC_JET_G0(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Value of normal velocity during the initial time interval BC_DT_0.

12.1.10.71. BC_DT_H(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

The time interval when normal velocity is equal to BC_Jet_gh.

12.1.10.72. BC_JET_GH(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Value of normal velocity during the interval BC_DT_h.

12.1.10.73. BC_DT_L(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

The interval when normal velocity is equal to BC_JET_gL.

12.1.10.74. BC_JET_GL(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Value of normal velocity during the interval BC_DT_L.

12.1.10.75. BC_SCALAR(BC, SCALAR EQ.)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq S c a l a r E q . \leq 100$

Boundary value for user-defined scalar equation.

12.1.10.76. BC_K_TURB_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Boundary value of K for K-Epsilon Equation.

12.1.10.77. BC_E_TURB_G(BC)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$

Boundary value of Epsilon for K-Epsilon Equation.

12.1.10.78. BC_PIC_MI_CONST_STATWT(BC, PHASE)¶

Data Type: DOUBLE PRECISION

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Flag to specify the constant statistical: weight for inflowing computational particles/parcels. Actual number of parcels will be automatically computed.

12.1.10.79. BC_PO_APPLY_TO_DES(BC)¶

Data Type: LOGICAL

$1 \leq B C \leq 500$

Flag to make the PO BC invisible to discrete solids.: Set this flag to .FALSE. to remove this BC for discrete solids.

12.1.10.80. BC_MI_APPLY_TO_DES(BC)¶

Data Type: LOGICAL

$1 \leq B C \leq 500$

Flag to make the PO BC invisible to discrete solids.: Set this flag to .FALSE. to remove this BC for discrete solids.

12.1.10.81. BC_SQP_RANDOM_Q(BC, PHASE)¶

Data Type: LOGICAL

$1 \leq B C \leq 500$
$1 \leq P h a s e \leq 10$

Flag to randomize SQP orientation (quaternion) along mass inlet BC.