Source code for RCAIDE.Library.Methods.Aerodynamics.Common.Drag.parasite_drag_nacelle
# RCAIDE/Library/Methods/Aerodynamics/Common/Drag/parasite_drag_nacelle.py
# (c) Copyright 2023 Aerospace Research Community LLC
#
# Created: Jun 2024, M. Clarke
# ----------------------------------------------------------------------------------------------------------------------
# IMPORT
# ----------------------------------------------------------------------------------------------------------------------
from RCAIDE.Framework.Core import Data
from RCAIDE.Library.Methods.Utilities import Cubic_Spline_Blender
from RCAIDE.Library.Methods.Aerodynamics.Common.Drag.compressible_turbulent_flat_plate import compressible_turbulent_flat_plate
# package imports
import numpy as np
# ----------------------------------------------------------------------------------------------------------------------
# Supersonic Parasite Drag Nacekke
# ----------------------------------------------------------------------------------------------------------------------
[docs]
def parasite_drag_nacelle(state,settings,geometry):
"""
Computes the parasite drag coefficient for all nacelles in the aircraft.
Parameters
----------
state : Data
Flight conditions and aerodynamic state
settings : dict
Aerodynamic analysis settings and parameters
geometry : Data
Aircraft geometry containing:
- networks : list
List of propulsion networks containing propulsors
- propulsors : list
List of propulsor objects with nacelle attributes
- nacelle : Nacelle, optional
Nacelle object to be analyzed
Returns
-------
None
Results are stored in state.conditions.aerodynamics.coefficients.drag.parasite[nacelle.tag]
Notes
-----
This function iterates through all propulsion networks and propulsors to identify
nacelles and compute their parasite drag coefficients using the nacelle_drag helper
function.
**Major Assumptions**
* All nacelles follow the same drag calculation methodology
* Nacelle drag is independent of other aircraft components
* Each nacelle has a unique tag for result storage
"""
# Estimating nacelle drag
for network in geometry.networks:
for propulsor in network.propulsors:
if propulsor.nacelle != None:
nacelle_drag(state,settings,propulsor.nacelle)
return
# ----------------------------------------------------------------------------------------------------------------------
# Nacelle Drag
# ----------------------------------------------------------------------------------------------------------------------
[docs]
def nacelle_drag(state,settings, nacelle):
"""
Computes the parasite drag coefficient for a single nacelle accounting for compressibility effects.
Parameters
----------
state : Data
Flight conditions containing:
- conditions.freestream.mach_number : float
Freestream Mach number [unitless]
- conditions.freestream.temperature : float
Freestream static temperature [K]
- conditions.freestream.reynolds_number : float
Freestream Reynolds number per unit length [unitless/m]
settings : dict
Aerodynamic analysis settings containing:
- supersonic.begin_drag_rise_mach_number : float
Mach number at which drag rise begins [unitless]
- supersonic.end_drag_rise_mach_number : float
Mach number at which drag rise ends [unitless]
nacelle : Data
Nacelle geometry containing:
- tag : str
Unique identifier for the nacelle
- diameter : float
Diameter of the nacelle [m]
- length : float
Length of the nacelle [m]
- areas.wetted : float
Wetted area of the nacelle [m²]
Returns
-------
None
Results are stored in state.conditions.aerodynamics.coefficients.drag.parasite[nacelle.tag]
Notes
-----
This function calculates the parasite drag coefficient for a nacelle using compressible
turbulent flat plate theory with form factor corrections. The calculation accounts for
compressibility effects and uses cubic spline blending for the transonic regime.
**Major Assumptions**
* Fully turbulent boundary layer over the entire nacelle
* Raymer's form factor correlation is valid for nacelle geometry
* Compressible turbulent flat plate skin friction correlation
* Cubic spline blending smooths transition between subsonic and supersonic regimes
* Nacelle shape can be approximated as a cylindrical body
**Theory**
The nacelle Reynolds number is:
:math:`Re_{nac} = Re \\cdot l_{nac}`
where :math:`Re` is the freestream Reynolds number per unit length and :math:`l_{nac}` is the nacelle length.
The skin friction coefficient is calculated using compressible turbulent flat plate theory:
:math:`C_f = f(Re_{nac}, M, T)`
The reference area is:
:math:`S_{ref} = \\pi \\cdot d_{nac} \\cdot l_{nac}`
where :math:`d_{nac}` is the nacelle diameter.
The form factor follows Raymer's correlation:
:math:`FF = 1 + \\frac{0.35}{l_{nac}/d_{nac}}`
For subsonic flow (M ≤ 1.0), the parasite drag coefficient is:
:math:`C_{D,parasite} = FF \\cdot C_f \\cdot \\frac{S_{wet}}{S_{ref}}`
For supersonic flow, the form factor is blended using a cubic spline:
:math:`FF_{eff} = FF \\cdot h_{00}(M) + 1 \\cdot (1-h_{00}(M))`
where :math:`h_{00}(M)` is the cubic spline blending function.
The final parasite drag coefficient is:
:math:`C_{D,parasite} = FF_{eff} \\cdot C_f \\cdot \\frac{S_{wet}}{S_{ref}}`
**Definitions**
'Nacelle Drag'
Parasite drag component caused by the nacelle's aerodynamic shape and surface friction.
'Form Factor'
Multiplier accounting for the increase in drag due to nacelle shape compared to a flat plate.
References
----------
[1] Stanford AA241 Course Notes
See Also
--------
RCAIDE.Library.Methods.Aerodynamics.Common.Drag.compressible_turbulent_flat_plate
RCAIDE.Library.Methods.Utilities.Cubic_Spline_Blender
"""
# unpack inputs
conditions = state.conditions
freestream = conditions.freestream
Mach = freestream.mach_number
T = freestream.temperature
Re = freestream.reynolds_number
low_mach_cutoff = settings.supersonic.begin_drag_rise_mach_number
high_mach_cutoff = settings.supersonic.end_drag_rise_mach_number
Sref = np.pi * nacelle.diameter * nacelle.length
Swet = nacelle.areas.wetted
# Reynolds number
Re_prop = Re*nacelle.length
# Skin friction coefficient
cf_prop, k_comp, k_reyn = compressible_turbulent_flat_plate(Re_prop,Mach,T)
# Form factor according to Raymer equation
form_factor = 1 + 0.35 / ( nacelle.length/nacelle.diameter)
if np.all((Mach<=1.0) == True):
# subsonic condition
parasite_drag = form_factor * cf_prop * Swet / Sref
else:
# supersonic condition
k_prop_sup = 1.
trans_spline = Cubic_Spline_Blender(low_mach_cutoff,high_mach_cutoff)
h00 = lambda M:trans_spline.compute(M)
form_factor = form_factor*(h00(Mach)) + k_prop_sup*(1-h00(Mach))
# find the final result
parasite_drag = form_factor * cf_prop * Swet / Sref
# store results
results = Data(
wetted_area = Swet ,
reference_area = Sref ,
total = parasite_drag ,
skin_friction = cf_prop ,
compressibility_factor = k_comp ,
reynolds_factor = k_reyn ,
form_factor = form_factor ,
)
state.conditions.aerodynamics.coefficients.drag.parasite[nacelle.tag] = results
return
