<boundary_conditions> Revised Formulation

As an extension to the solver deck entries mentioned above, ultraFluidX 2024.0 and beyond allows you to specify boundary conditions in a revised formulation to allow for more flexibility.

Boundary conditions can be set as follows:

Note: This revised formulation supersedes some entries previously located in the <simulation> <general> tab. The entries that can be replaced by the revised boundary condition formulation are:

<reference_velocity>: This is now the <velocity> <x_dir> value of the <inlet_instance>.
<moving_ground>: This information is represented by a <wall_instance> of type moving on the domain ground.
<rotating_wheels>: This is replaced by <wall_intances> of type <rotating> with a non-zero rotational speed for the wheels.

Besides, while the following entries on boundary layer suction can still be used, the information conveyed by the entries can be represented by the revised boundary conditions:

<boundary_layer_suction>: true
<boundary_layer_suction_position>: x position

These entries can be replaced by setting the domain ground to a “slip” ground and adding a domain_part_instance with “static” boundary condition starting at the suction position. This static patch needs to be excluded from the force coefficient calculation by making it a static patch.

<boundary_conditions>-<inlet>

One or more inlet instances can be defined. If no inlet instance is defined, the domain boundary at the x_min position will be used.

<inlet_instance>: <name> default: uFX_inlet; Indicating a name for the inlet instance.
<parts>: <name> default: uFX_domain_x_min; The parts which are to be used for an inlet boundary. By default, the wind tunnel patch at x_min position will be used, which is named uFX_domain_x_min.
<fluid_bc_settings>: <type> string, default: velocity; <velocity>; <x_dir>; <y_dir>; <z_dir>

<boundary_conditions>-<outlet>

One or more outlet instances can be defined. If no outlet instance is defined, the domain boundary at the x_max position will be used.

<outlet_instance>: <name> default: uFX_outlet
<parts>: <name> default: uFX_domain_x_max; The parts which are to be used for an outlet boundary. By default, the wind tunnel patch at x_max position will be used, which is named uFX_domain_x_max.
<fluid_bc_settings>: <type> string, default: non_reflective_pressure

<boundary_conditions>-<wall>

This category allows for specifying a range of different conditions that will describe all surfaces of the geometry, as well as patches defined on domain boundary. Every run will usually have several wall instances, which are then followed by further specifications:

<wall_instance>

<name> name of the instance.

<parts>

<name> name of the stl parts or domain part instances to be included.

<fluid_bc_settings>

This category contains the main specifications for the BC behavior. Options are:

<type> slip

No further entries needed.

<type> static

No further entries needed.

<wall_model_variant>

Modify the wall model setting for that boundary patch to using a variant defined in the <simulation><wall_modeling> category.

<type> rotating

Requires additional entries:

<rpm>: Rotational speed in rpm.
<center>: Location of the center point of the rotation.; <x_pos>; <y_pos>; <z_pos>
<axis>: Orientation of the rotational axis.; <x_dir>; <y_dir>; <z_dir>
<roughness>: Optional value for surface roughness.
<wall_model_variant>: Modify the wall model setting for that boundary patch to using a variant defined in the <simulation><wall_modeling> category.

<type> moving

Requires additional entries:

<velocity>: <x_dir>; <y_dir>; <z_dir>
<roughness>: Optional value for surface roughness.
<wall_model_variant>: Modify the wall model setting for that boundary patch to using a variant defined in the <simulation><wall_modeling> category.

<boundary_conditions>-<periodicity>

This category allows you to define global directions for which the domain boundaries are to be treated as periodic.

The direction in which the periodic boundary condition is applied can be set by the elements

<x_dir> [true / false: default false]

<y_dir> [true / false: default false]

<z_dir> [true / false: default false]

Note: For using the periodic boundary condition, at least 8 voxels in the respective direction are required.