Farfield

Farfield#

A farfield volume zone defines the outer boundaries of your computational domain. It establishes the limits where freestream conditions are applied and ensures proper flow development around your geometry.

Availability by workflow#

The mesher, and whether the project started from a geometry or from a surface mesh, decide which types are offered and whether a half-model can be requested. Check this before choosing a Type.

Type

Offered with

Half-model support

Automated farfield

any mesher, from a geometry or a surface mesh

From a geometry, GeometryAI with the beta mesher. From a surface mesh, the beta mesher alone

User defined farfield

any mesher, from a geometry or a surface mesh

GeometryAI with the beta mesher

Wind tunnel

GeometryAI only

GeometryAI with the beta mesher, set in the wind tunnel section

With the Legacy mesher no half-model is available on any type, because the split is performed by the beta mesher.

Available Options#

Option

Description

Applicable

Type

Method of constructing the farfield

always

Domain type

Whether to mesh the full body or a half-model, and which side to keep

beta mesher, plus GeometryAI when starting from a geometry. Not on Wind tunnel, which has its own in the wind tunnel section

Method

Method for determining farfield shape

Type is Automated farfield

Width

Width of the wind tunnel (Y-direction)

Type is Wind tunnel

Height

Height of the wind tunnel (Z-direction)

Type is Wind tunnel

Inlet X position

X-position of the tunnel inlet

Type is Wind tunnel

Outlet X position

X-position of the tunnel outlet

Type is Wind tunnel

Floor Z position

Z-position of the tunnel floor

Type is Wind tunnel

Floor geometry

Type of floor configuration

Type is Wind tunnel

Friction patch X

X-range of the friction patch on the floor

Floor geometry is Fixed floor

Friction patch width

Width of the friction patch

Floor geometry is Fixed floor

Center belt X

X-range of the central moving belt

Floor geometry is Center-belt wind tunnel or Wheel-belt wind tunnel

Center belt width

Width of the central moving belt

Floor geometry is Center-belt wind tunnel or Wheel-belt wind tunnel

Front wheel belts X

X-range of the front wheel belts

Floor geometry is Wheel-belt wind tunnel

Front wheel belts Y

Y-range (inner to outer) of the front wheel belts

Floor geometry is Wheel-belt wind tunnel

Rear wheel belts X

X-range of the rear wheel belts

Floor geometry is Wheel-belt wind tunnel

Rear wheel belts Y

Y-range (inner to outer) of the rear wheel belts

Floor geometry is Wheel-belt wind tunnel

Detailed descriptions#

Type#

Setting allowing the user to choose between generating the farfield in the workflow and providing the farfield as a part of uploaded geometry.

Possible selections:

  • Automated farfield - Farfield generated by Flow360 around the geometry

  • User defined farfield - Farfield geometry provided by the user, has to be assigned to an appropriate boundary condition in Boundary conditions

  • Wind tunnel - Analytic wind tunnel geometry with configurable dimensions and floor types

Notes:

  • Wind tunnel option is only available with GeometryAI.

  • Wind tunnel keeps its half-model controls in the wind tunnel section rather than under Domain type.

  • By default, the volume mesher will grow boundary layers on User defined farfield and Wind tunnel boundaries. Use Passive Spacing to project or disable boundary layer growth.

Domain type#

Specifies whether to mesh the full body or a half-model, and which side of the Y=0 plane to keep.

  • Default: Auto-detect

Possible selections:

  • Auto-detect - Infer the domain from the geometry bounding box: a half-model when the geometry lies on one side of Y=0, the full body otherwise

  • Full body - Keep the entire domain without attempting to add symmetry planes

  • Half-body +Y - Trim to a half-model by slicing at Y=0 and keep the positive Y side

  • Half-body -Y - Trim to a half-model by slicing at Y=0 and keep the negative Y side

Notes:

  • A half-model splits the domain at Y=0 and meshes and simulates only one side, which significantly reduces computational cost for symmetric geometries

  • Selecting a half-model or Full body explicitly overrides the automatic detection that Auto-detect performs

  • Surfaces lying entirely on the discarded side are dropped from the mesh. If the whole geometry sits on that side, the case is rejected rather than meshed empty

  • See Availability by workflow for which meshers and project sources offer this control

Method#

Method of defining the size of an auto-generated farfield.

Possible selections:

  • Auto: Automatically determines appropriate farfield dimensions based on geometry (default radius is 50× the maximum bounding box dimension)

    • Generates a full sphere if geometry extends across Y=0

    • Creates +Y semi-sphere if geometry is entirely above Y=0

    • Creates -Y semi-sphere if geometry is entirely below Y=0

  • Quasi-3D: Creates a thin disk for quasi-3D simulations

    • Both sides of the farfield disk are treated as symmetric planes

Wind tunnel parameters#

The following parameters define the wind tunnel geometry when Type is set to Wind tunnel.

Width#

Width of the wind tunnel in the Y-direction.

  • Default: 10 m

  • Units: Length

Height#

Height of the wind tunnel in the Z-direction.

  • Default: 6 m

  • Units: Length

Inlet X position#

X-coordinate of the tunnel inlet plane.

  • Default: -20 m

  • Units: Length

Note: Must be less than Outlet X position.

Outlet X position#

X-coordinate of the tunnel outlet plane.

  • Default: 40 m

  • Units: Length

Note: Must be greater than Inlet X position.

Floor Z position#

Z-coordinate of the tunnel floor.

  • Default: 0 m

  • Units: Length

Floor geometry#

Specifies the type of floor configuration for the wind tunnel.

Possible selections:

  • Fixed floor - Static floor with a friction patch region where wall boundary conditions apply

  • Fully-moving road - Entire floor moves at freestream velocity to simulate road motion

  • Center-belt wind tunnel - Floor with a central moving belt surrounded by stationary regions

  • Wheel-belt wind tunnel - Floor with a central belt plus four additional wheel belt regions for automotive simulations

Fixed floor parameters#

The following parameters are available when Floor geometry is set to Fixed floor.

Friction patch X#

X-range (minimum, maximum) defining the extent of the friction patch on the floor.

  • Default: (-3, 6) m

  • Units: Length

Notes:

  • The friction patch applies wall boundary conditions within this X-range

  • Must be within the inlet and outlet X positions

Friction patch width#

Width of the friction patch centered at Y=0.

  • Default: 2 m

  • Units: Length

Note: Must be less than the wind tunnel width.

Center-belt wind tunnel parameters#

The following parameters are available when Floor geometry is set to Center-belt wind tunnel or Wheel-belt wind tunnel.

Center belt X#

X-range (minimum, maximum) defining the extent of the central moving belt.

  • Default: (-2, 2) m

  • Units: Length

Note: Must be within the inlet and outlet X positions.

Center belt width#

Width of the central moving belt centered at Y=0.

  • Default: 1.2 m

  • Units: Length

Note: Must be less than the wind tunnel width.

Wheel-belt wind tunnel parameters#

The following parameters are available when Floor geometry is set to Wheel-belt wind tunnel. These are in addition to the center belt parameters.

Front wheel belts X#

X-range (minimum, maximum) defining the extent of the front wheel belts.

  • Required

  • Units: Length

Note: Maximum X must be less than the minimum X of the rear wheel belts.

Front wheel belts Y#

Y-range (inner edge, outer edge) defining the lateral position of the front wheel belts.

  • Required

  • Units: Length

Notes:

  • The inner edge must be greater than half the center belt width

  • The outer edge must be less than half the wind tunnel width

  • Belts are symmetric about Y=0

Rear wheel belts X#

X-range (minimum, maximum) defining the extent of the rear wheel belts.

  • Required

  • Units: Length

Note: Minimum X must be greater than the maximum X of the front wheel belts.

Rear wheel belts Y#

Y-range (inner edge, outer edge) defining the lateral position of the rear wheel belts.

  • Required

  • Units: Length

Notes:

  • The inner edge must be greater than half the center belt width

  • The outer edge must be less than half the wind tunnel width

  • Belts are symmetric about Y=0

💡 Tips

  • Automated farfield is generally preferred for aerospace applications

  • Wind tunnel is ideal for automotive simulations requiring realistic ground effects

  • Use Wheel-belt wind tunnel floor geometry to match physical wind tunnel configurations with separate wheel pads

  • When using symmetry plane with wind tunnels, ensure your geometry is symmetric about Y=0

❓ Frequently Asked Questions

  • How do I choose between Auto and Quasi-3D farfield methods?

    Use Auto for full 3D simulations and Quasi-3D for 2D or axisymmetric cases where the flow is primarily in one plane.

  • When should I use the Wind tunnel farfield type?

    Use Wind tunnel for automotive CFD simulations where you need to model realistic wind tunnel conditions including moving floor/belts and proper inlet/outlet boundary conditions.

  • What is the difference between Fixed floor and Fully-moving road?

    Fixed floor has a stationary floor with a friction patch where boundary layer develops. Fully-moving road simulates the entire floor moving at freestream velocity, eliminating floor boundary layer effects, ideal for simulating on-road conditions.

  • How do wheel belts work?

    Wheel belts are small moving belt regions positioned under each wheel location. They move at freestream velocity to simulate tire contact with the road while the surrounding floor remains stationary.

🐍 Python Example Usage

See also

Python API:

import flow360 as fl

# Automated farfield volume zone (full/semi-sphere sized from the geometry bounding box)
farfield = fl.AutomatedFarfield(name="Farfield", method="auto")

# Request a half-model explicitly instead of letting the mesher infer the domain
# from the geometry bounding box. Also accepted: "half_body_negative_y" and
# "full_body". Requires the beta mesher, plus the GeometryAI surface
# mesher when the project starts from a geometry. Starting from a surface mesh,
# only the automated farfield honours it.
half_body_farfield = fl.AutomatedFarfield(
    name="Farfield",
    method="auto",
    domain_type="half_body_positive_y",
)

# The farfield is added to the meshing parameters' volume_zones list
meshing = fl.MeshingParams(
    defaults=fl.MeshingDefaults(
        surface_max_edge_length=1 * fl.u.m,
        boundary_layer_first_layer_thickness=1e-5 * fl.u.m,
    ),
    volume_zones=[farfield],
)