4. Boundary Conditions

4.1. Boundary Condition List

You will probably want the table of boundary conditions below available. When processing your grid, use either the indices in the first column or the second column. When you get your results back, the forces that are summarized in the [project].forces file will be labeled using the notation in the second column. This is done so that existing boundary condition flags may be used, while still allowing for 4-digit boundary conditions in the solver, which enable room for future growth. _Note that if you want to change a boundary condition, you must pre-process the grid over again. The BC indices are hardwired into the partition files._ This is on our to-do list to change.

Grid Index FUN3D Index Description Notes
6661 6661 Symmetry Plane x plane only: enforces zero crossflow velocity
6662 6662 Symmetry Plane y plane only: enforces zero crossflow velocity
6663 6663 Symmetry Plane z plane only: enforces zero crossflow velocity
3 5000 Farfield Riemann invariant node based
4 4000 Viscous strong enforcement of no-slip condition
5 3000 Tangency weak enforcement of zero normal velocity through fluxes
6100 6100 Periodicity Discrete periodicity, limited to nominally 2D grids extruded across n planes in a third dimension

Element Based Boundary Conditions ( Version 10.5 )—Values ( where required ) set up in &boundary_conditions namelist in namelist.input (fun3d.nml for versions 10.9.0 and later)

Grid Index FUN3D Index Description Notes
5025 5025 Farfield Riemann invariants
5026 5026 Extrapolate Supersonic outflow
5050 5050 Farfield Freestream
5051 5051 Back pressure Specified static pressure (allows supersonic flow)
5052 5052 Back pressure2 Static pressure set by specified Mach number ( M < 1 )
7011 7011 Subsonic inflow Subsonic inflow (pt,Tt) for nozzle plenum
7012 7012 Subsonic outflow Subsonic outflow (p0) for inlet duct
7031 7031 Mass flow out Specification of massflow out of the control volume
7036 7036 Mass flow in Specification of massflow in to the control volume
7100 7100 Fixed inflow Fixed primitive variables in to control volume

4.2. Value Input Format (Version 11.0)

For code released at 10.8.0 or later, a change in the boundary condition input format has been made. The patch number associated with a boundary condition now used to directly index the physical conditions. bc_count and bc_patch(n) are no longer used.

Please report any problems, inconsistencies, issues, etc. with the new boundary_conditions input to FUN3D Support.

 ! This file contains namelists used for specifying inputs to
 ! FUN3D. For versions 10.8 and later, the following namelists 
 ! apply (if a namelist is not present, its variables take on 
 ! their default values):
 !    boundary_conditions
 !

 &boundary_conditions
    grid_units = 'meters'
                       ! options: meters, inches, millimeters
                       ! DEFAULT=meters
                       | Used in dimensional unit conversion
    massflow_dimensions = 'nondim'
                       ! options: metric (kg/s), nondim (mesh units squared)
                       ! DEFAULT=metric
                       | Used in dimensional unit conversion
    total_pressure_ratio(n) = 1
                       ! Input for BC 7011 associated with bc patch number -n-
                       ! DEFAULT=1
    total_temperature_ratio(n) = 1
                       ! Input for BC 7011 associated with bc patch number -n-
                       ! DEFAULT=1
    subsonic_inflow_velocity(n) = 'normal'
                       ! Direction of inflow velocities for BC 7011 
                       ! associated with bc patch number -n-
                       ! options: 'normal', 'alpha,beta'
                       ! DEFAULT='normal'
    alpha_bc(n) = 0.0
                       ! Input for BC 7011 associated with bc patch number -n-
                       ! DEFAULT=0.0
    beta_bc(n)  = 0.0
                       ! Input for BC 7011 associated with bc patch number -n-
                       ! DEFAULT=0.0
    static_pressure_ratio(n) = 1
                       ! Input for BC 7012, 5051 associated with bc patch number -n-
                       ! DEFAULT=1
    mach_bc(n) = 0
                       ! Input for BC 5025 patch number associated with bc patch number -n-
                       ! DEFAULT=0
    q_set(n,5) = 0
                       ! Input for BC 7100, 7105 associated with bc patch number -n-
                       ! DEFAULT=(0.,0.,0.,0.,0.)
    massflow(n) = 0
                       ! Input for BC 7031, 7036 associated with bc patch number -n-
                       ! DEFAULT=0
    wall_temperature(n) = 1
                       ! Input for BC associated with patch number -n-
                       ! Sets Twall/Tref value. (Note that corresponding
                       ! wall_temp_flag(n) must be set to .true.)
                       ! DEFAULT=1
    wall_temp_flag(n) = .false.
                       ! Input for BC associated with patch number -n- to activate
                       ! use of wall temperature input
                       ! DEFAULT=.false.
    !
    !-------------------------------------------------------------
    !-------------------------------------------------------------
 /

Note that the above namelist file contains many input variables, but in general it is not necessary to list them all. One can instead rely on the fact that most of the defaults are often desired, and only those variables that are different from the defaults need to be given. The following might be an example of a typical namelist file for a calorically-perfect FUN3D run:

Sample Boundary Condition Namelists

Subsonic inflow / nozzle bc – BC 7011

This is an example of a mesh in inches, one total pressure-total temperature boundary condition associated with patch 3, with the inflow velocity set normal to the patch (default setting) for a pressure ratio of 1.6 ( inflow total pressure normalized by reference static pressure ) and a temperature ratio of 1.0 ( inflow total temperature normalized by reference static temperature).

The non-dimensional freestream static pressure in FUN3D is 1/g and is the same as the reference static pressure.. Total_pressure_ratio is the same as nozzle pressure ratio for propulsion simulations.

&boundary_conditions
  total_pressure_ratio(3)    = 1.6,
  total_temperature_ratio(3) = 1.0,
/

Inlet bc Example 1 – BC 7031

This is a sample for an inlet with one mass flow out of the control volume boundary associated with patch 1, with a mass flow rate of 0.25 in units of mesh units squared. The desired massflow in this example is ramped from 0 to the set condition of 0.25 over 500 iterations as set by flow_mflux_ramp.

&boundary_conditions
  massflow(1)           = 0.25,
  inlet_solution_method = 'massflux',
/
&component_parameters
  flow_mflux_ramp=500,
/

Inlet bc Example 2 – BC 7012

This is a sample for an inlet mesh with a specified static pressure ratio of 0.9 associated with patch 5. This is the static pressure required at the outflow boundary normalized by the reference static pressure.

&boundary_conditions
  static_pressure_ratio(5) = 0.9,
/

Fixed Inflow/Outflow – BC 7100/7105

Patch 8 is a fixed inflow or outflow boundary setting the normalized density to 1, the normalized velocities of u, v, and w to 0.5, 0.0, and 0.0 respectively and the pressure to 0.714.

&boundary_conditions
  q_set(8,:) = 1.0, 0.5, 0.0, 0.0, 0.714,
/

Total Pressure Inflow/Static Pressure Outflow – BC 7011-7012

Patch 5 is a total pressure—total temperature boundary condition associated assuming alpha=0 and beta=0 with the total pressure ratio of 1.984 and a total temperature ratio of 1.201. The total pressure ratio is ramped from 1.0 to 1.984 over 100 iterations via the parameter inflow_pt_ramp. The second boundary condition patch is 6 and is a static pressure ratio and static temperature ratio boundary set to the conditions of 1.364 and 1.0 respectively.

&boundary_conditions
  total_pressure_ratio(5)    = 1.984
  total_temperature_ratio(5) = 1.201
  static_pressure_ratio(6)   = 1.364
/
&component_parameters
  inflow_pt_ramp=100
/

Specified Mach Number – BC 5052

The Mach number of 0.5 is specified for patch 5.

&boundary_conditions
  mach_bc(5) = 0.5
/

Static Pressure for Flow Out of Control Volume – BC 5051

The static pressure ratio of 0.25 is specified for patch 2.

&boundary_conditions
  static_pressure_ratio(2) = 0.25
/