"""Cf recipe -- per-body directional force coefficient (own-area basis).
Two normalisation conventions produce a force coefficient, and they use
different aggregations:
- **Own-area basis** (this recipe): normalise by the body's own wetted
area ``A_total``. Then
Cf_i = (1 / A_total) * sum_k cp_k * area_k * n_k,i
= area_weighted_mean_k(cp_k * n_k,i),
because the ``area_k`` weights sum to ``A_total`` and cancel. So the
**area-weighted mean** of the per-direction Cp component *is* the force
coefficient on the own-area basis. This recipe takes pre-existing
``cp_<dir> = cp * n_<dir>`` fields and area-weight-means them per body.
- **Reference-area basis** (the ``fixtures/tests/pressure/templates/cf.yaml``
template): normalise by an independent ``A_ref`` (e.g. a frontal area).
Then ``A_ref != A_total`` does not cancel and Cf is a **sum** of
``force_contribution`` (``-cp*area*n / A_ref``) per body. Use this when
a fixed reference area is required so Cf converts back to force
unambiguously.
Contrast with :mod:`cfdmod.core.recipes.cm`, which always *sums* moment
contributions (there is no own-area cancellation for a moment). The caller
must supply the ``cp_<dir>`` fields for this recipe -- no built-in op
produces them; the reference-area path uses ``force_contribution`` instead.
Given a Cp data source with a ``"body"`` grouping (triangle -> body id)
and per-direction ``cp_<dir>`` fields, the recipe builds a
:class:`GroupsDataSource` with one output field per direction, all on the
same groups data source.
"""
from __future__ import annotations
__all__ = ["CfRecipeConfig", "cf_pipeline"]
from typing import Literal
from pydantic import BaseModel, ConfigDict
from cfdmod.core.data_source import DataSource, GroupsDataSource
from cfdmod.core.ops.data_source_create.field_series_for_groups import (
FieldSeriesForGroupsParams,
field_series_for_groups,
)
[docs]
class CfRecipeConfig(BaseModel):
"""Cf recipe parameters.
Attributes:
grouping: Name of the grouping in ``ds.groupings`` that maps
triangles to body ids.
directions: Field-name suffixes per force direction. The recipe
aggregates ``cp_<dir>`` for each entry. Defaults to the
three Cartesian components.
prefix: Source field prefix (``"cp"`` for the standard
convention).
"""
model_config = ConfigDict(frozen=True)
grouping: str
directions: list[Literal["x", "y", "z"]] = ["x", "y", "z"]
prefix: str = "cp"
def cf_pipeline(cfg: CfRecipeConfig):
"""Return a single-arg callable producing a :class:`GroupsDataSource`."""
def run(ds: DataSource) -> GroupsDataSource:
result: GroupsDataSource | None = None
for d in cfg.directions:
field_in = f"{cfg.prefix}_{d}"
field_out = f"cf_{d}"
partial = field_series_for_groups(
ds,
FieldSeriesForGroupsParams(
grouping=cfg.grouping,
field=field_in,
agg="area_weighted_mean",
out=field_out,
),
)
if result is None:
result = partial
else:
arr = partial.fields.read(field_out)
meta = partial.field_meta[field_out]
result = result.with_field(field_out, arr, meta=meta)
assert result is not None
return result
return run
AeroSim Docs