"""Aerodynamic polar data."""
# This file is part of FAST-OAD : A framework for rapid Overall Aircraft Design
# Copyright (C) 2021 ONERA & ISAE-SUPAERO
# FAST is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
from numpy import ndarray
from scipy.interpolate import interp1d
from scipy.optimize import fmin
[docs]class Polar:
def __init__(self, cl: ndarray, cd: ndarray):
"""
Class for managing aerodynamic polar data.
Links drag coefficient (CD) to lift coefficient (CL).
It is defined by two vectors with CL and CD values.
Once defined, for any CL value, CD can be obtained using :meth:`cd`.
:param cl: a N-elements array with CL values
:param cd: a N-elements array with CD values that match CL
"""
self._definition_CL = cl
self._cd = interp1d(cl, cd, kind="quadratic", fill_value="extrapolate")
def _negated_lift_drag_ratio(lift_coeff):
"""Returns -CL/CD."""
return -lift_coeff / self.cd(lift_coeff)
self._optimal_CL = fmin(_negated_lift_drag_ratio, cl[0], disp=0)
@property
def definition_cl(self):
"""The vector that has been used for defining lift coefficient."""
return self._definition_CL
@property
def optimal_cl(self):
"""The CL value that provides larger lift/drag ratio."""
return self._optimal_CL
[docs] def cd(self, cl=None):
"""
Computes drag coefficient (CD) by interpolation in definition data.
:param cl: lift coefficient (CL) values. If not provided, the CL definition vector will be
used (i.e. CD definition vector will be returned)
:return: CD values for each provide CL values
"""
if cl is None:
return self._cd(self._definition_CL)
return self._cd(cl)