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propeller.py
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propeller.py
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" propeller model "
from numpy import pi
from gpkit import Model, parse_variables, SignomialsEnabled, SignomialEquality
class Propeller_Performance(Model):
""" Propeller Model
Variables
---------
T [lbf] thrust
Tc [-] coefficient of thrust
etaadd 0.7 [-] swirl and nonuniformity losses
etav 0.85 [-] viscous losses
etai [-] inviscid losses
eta [-] overall efficiency
z1 self.helper [-] efficiency helper 1
z2 [-] efficiency helper 2
lam [-] advance ratio
CT [-] thrust coefficient
CP [-] power coefficient
Q [N*m] torque
omega [rpm] propeller rotation rate
omega_max 10000 [rpm] max rotation rate
P_shaft [kW] shaft power
M_tip .5 [-] Tip mach number
a 295 [m/s] Speed of sound at altitude
"""
def helper(self, c):
return 2. - 1./c[self.etaadd]
def setup(self,parent, state):
exec parse_variables(Propeller_Performance.__doc__)
V = state.V
rho = state.rho
R = parent.R
constraints = [eta <= etav*etai,
Tc >= T/(0.5*rho*V**2*pi*R**2),
z2 >= Tc + 1,
etai*(z1 + z2**0.5/etaadd) <= 2,
lam >= V/(omega*R),
CT >= Tc*lam**2,
CP <= Q*omega/(.5*rho*(omega*R)**3*pi*R**2),
eta >= CT*lam/CP,
omega <= omega_max,
P_shaft == Q*omega,
(M_tip*a)**2 >= (omega*R)**2 + V**2
]
return constraints, state
class Propeller(Model):
""" Propeller Model
Variables
---------
R [ft] prop radius
W [lbf] prop weight
K 4e-4 [1/ft^2] prop weight scaling factor
T_m_static 40. [lbf] prop max static thrust
"""
flight_model = Propeller_Performance
def setup(self):
exec parse_variables(Propeller.__doc__)
constraints = [W >= K*T_m_static*R**2]
return constraints