Template Case file¶

The structure of a Template Case .py file. Most settings can also be changed in the Template Case editor, which writes them back into the file. For a complete working example, see isolated-front-wing.py in the tutorial example data.

Structure¶

A Template Case is a Python module that defines one class, CFDModel, with settings as class attributes:

from bramble.core.geometry import Point, Bounds, Vector
from chickweed.model import FeaturedCFDModel   # CCMFeaturedCFDModel for Star-CCM+

API_VERSION = 1

class CFDModel(FeaturedCFDModel):
    velocity = 50.0
    solution_stages = [
        {'solver': 'potential', 'iterations': 0},
        {'solver': 'RANS', 'iterations': 4000},
    ]
    # ...

API_VERSION = 1 and a class named CFDModel are required.
The base class is FeaturedCFDModel for OpenFoam, OpenFoam with CHT and Acoustic, and CCMFeaturedCFDModel for Star-CCM+. Import only the base class you use. Importing the other one makes Bramble treat the file as the other type.
Bramble runs the file on its servers when you upload or save it, so it must be self-contained. Only import from bramble.core.geometry (Point, Vector, Bounds), bramble.cfd.case.components and chickweed.model. Helper functions and constants in the file are fine.
Saving from the editor rewrites the attributes it edits as literal values.

Units¶

Lengths are in metres. The exceptions are the Star-CCM+ prism-layer thickness and base size, which are in mm.
Velocity in m/s, angles in degrees, density in kg/m³, pressure in Pa, temperature in K, kinematic viscosity in m²/s, and memory in GB.
Uploaded geometry is in millimetres. See coordinate system and units.

Validation messages¶

Cause	Message
`API_VERSION` or `CFDModel` missing	"Can't find '<name>', which is required to process this template case"
Syntax or indentation error	"SyntaxError found on line <n>: …" (or IndentationError, and so on)
File can't be read	"Import of template case with error: … Was it a valid python file?"
Settings for the wrong base class	"Invalid keys: …", e.g. `wheels` in a Star-CCM+ file, or `ccm_wheels` in an OpenFOAM one
Other errors on save	"Error in template case …"
The Template Case is locked	"Template case is being used by a case and cannot be replaced"

Main attributes¶

Simulation¶

Attribute	Default	Notes
`solution_stages`	—	A list of `{'solver', 'iterations', 'time_step'}`. Solvers: `'potential'`, `'RANS'`, `'RANS LIMITED'`, `'DES'`, and the CHT stages. For transient stages, `iterations` is the solution time in seconds
`averaging_window`	500	Iterations (or time steps) to average over. For DES: averaging time ÷ time step
`output_interval`	500
`convergence_criteria`	—	`{'start_time', 'n_times_unconverged', 'monitors': [{'force_group', 'direction': 0/1/2, 'type', 'tolerance'}]}`. Direction 0 = drag, 1 = side, 2 = lift. `{}` turns it off
`resource`	96 partitions, 3.0 GB/core	`{'nr_partitions', 'nr_mesh_partitions', 'memory_per_core'}`
`meancalc_settings`, `mc_stopping_criteria`	—	MeanCalc workflows only

Example transient (DES) stages:

solution_stages = [
    {'solver': 'potential', 'iterations': 0},
    {'solver': 'RANS', 'iterations': 0.5, 'time_step': 0.001},
    {'solver': 'DES', 'iterations': 1.5, 'time_step': 0.00025},
]

Domain and reference values¶

Attribute	Default	Notes
`velocity`	50	Used when the Map doesn't set velocity
`yaw`	0
`ref_density`, `ref_pressure`, `ref_temperature`, `ref_viscosity`	1.225, 0, 303.15, 1.41e-5
`ref_area`	frontal area	Used for coefficients
`location_in_mesh`	—	`Point(x, y, z)` inside the fluid
`domain`	—	`(Point1, Point2, Point3, height)`: three ground-plane corners and the height
`domain_nr_cells`	—	`[nx, ny, nz]`
`half_domain`	False	Bramble adjusts the domain itself
`ground_patch`, `nr_car_points`	False	Refined ground patch and its extent in ground cells

Mesh recipe¶

Attribute	Notes
`mesh_defaults`	`{'surface', 'proximity', 'curvature', 'feature_edge'}` settings applied to every component
`components`	`({'name', 'regex', 'mesh': {...}},)`. A component's `mesh` settings override the defaults for its zones
`mesh_ref_boxes`	`{'name': {'level': 7, 'bounds': Bounds([xmin, xmax, ymin, ymax, zmin, zmax])}}`
`mesh_ref_geometry`	Parts used as refinement regions, e.g. `{'regex': 'refine-rs', 'level': 6, 'distance': 0.0015, 'mode': 'distance'}`

Mesh settings:

Setting	Keys
`surface`	`level`, `nr_layers`, `expansion_ratio`, `final_layer_ratio`, `min_thickness`, `first_layer_thickness`, `gap`, `passive`
`proximity`	`level`, `distance` (m)
`curvature`	`on`, `curvature`, `level_increment`
`feature_edge`	`on`, `feature_angle`, `level`, `min_length`, `levels: [(distance, level), …]`

Any setting can also have: - regex, to apply to only some zones in the component - default: True, a lower-priority fallback - workflow (see below)

Regular expressions match zone names as in the rest of Bramble. See zone naming.

Settings for specific workflows¶

Add 'workflow': '<regex>' to a component mesh setting to apply it only when the Attitude's workflow name matches. The match starts at the beginning of the name and is case-sensitive, so use .* either side to match anywhere:

components = (
    {'name': 'BrakeDiscs', 'regex': '.*disc.*', 'mesh': {
        'surface': (
            {'level': 9, 'nr_layers': 2},
            {'level': 11, 'nr_layers': 5, 'workflow': '.*Thermal.*'},  # only in thermal workflows
        )}},
)

This applies to component mesh settings (surface, proximity, curvature and feature edges), not to refinement boxes. Check the exact workflow names on your Attitudes' CFD Setup.

Boundary conditions, rotation and porous zones¶

Attribute	Contents
`velocity_inlets`, `velocity_outlets`, `total_pressure_inlets`, `pressure_outlets`, `slippy_walls`, `roughness`, `temperatures`, `grounds`	Lists of `{'component', 'regex', …values}`. `component` must match a name in `components`. Give grounds `'tags': ['ground__ground']`
`wheels`	Rotating regions with an MRF: `{'name', 'regex', 'axis', 'origin', 'omega', 'mrf_point', 'non_rotating_patches', 'zoneless', 'zoneless_patches'}`
`rotating`	Rotating walls without an MRF: `{'name', 'regex', 'axis', 'origin', 'omega'}`
`radiators`	`{'name', 'point', 'coefficients': (darcy, forchheimer), 'coordinate_system': (through, orthogonal), 'factors': (1, 10, 10), 'up_down'}`
`porous_jumps`, `fan_jumps`, `mfps`	Interior zones

Forces, monitors and exports¶

Attribute	Contents
`solve_forces`	`[{'name', 'regex'}]`. Include an `all` group
`solve_monitors`	`[{'regex', 'type', 'variable'}]` on `toint` surfaces
`solve_balances`	`({'name': 'pitch', 'centre': Point(...), 'span': ...},)`
`export_surfaces`, `export_movies`, `export_custom_movies`, `export_iso_surfaces`, `export_volumes`, `export_point_probes`, `export_surface_probes`, streamline exports	See the editor reference for fields