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230 | # Applied Python PRISM
# (PRISM) PaRametrIc System Model
#
# Written by Charlie Taylor <cet@appliedpython.com>
# Sep 7, 2007
from prism.MassItem import MassItem
from math import *
from prism.utils import Constants
from prism.Summary import Summary
from prism.isp import Nozzle_Eff
#from prism.props.refprop7.n23_fluid import n_fluid
from prism.props.refprop7.n_dll_fluid import n_fluid
from prism.isp import isp
from prism.props import Materials
from prism.utils import mensuration
class Engine_ColdGas( MassItem ):
'''Note that cold gas thrusters get about the same thrust with any gas.
Isp goes like sqrt( T/M )
wdot goes like sqrt( M/T )
So a given throat size and area ratio get about the same thrust
'''
def __init__(self, name="ColdGasEngine", mass_lbm=0.0, gasSymbol='He',
Tin=530.0, matlBody="SS",
cxw=1.0, Pc=150.0, Fvac=1.0, eps=50.0, CR=2.5, LoverDt=4.0,
etaCham=0.97, etaNoz=0.99, isBell=1, pcentBell=80.0,
halfAngDeg=15.0, Number=1, calcEtaNoz=1):
MassItem.__init__(self, name, type="inert")
self.Number = Number # number of engines
self.gasSymbol = gasSymbol
self.matlBody = matlBody
self.rhoBody, self.syBody, self.eBody, self.tmingBody = Materials.getMatlProps(matlBody)
self.Fvac = Fvac
self.Pc = Pc
self.Tin = Tin
self.eps = eps
self.CR = CR
self.LoverDt = LoverDt
self.cxw = cxw
self.etaCham = etaCham
self.etaNoz = etaNoz
self.calcEtaNoz = calcEtaNoz
self.isBell = isBell
self.pcentBell = pcentBell
self.halfAngDeg = halfAngDeg
self.gas = n_fluid(symbol=gasSymbol, T=Tin, P=Pc, child=1)
self.reCalc()
def reCalc(self):
# set design variables
self.gas.setTP(T=self.Tin,P=self.Pc)
Gam = self.gas.gamma()
Pamb = 0.0
self.IspODE = isp.calcidealis(Gam,self.Tin,self.gas.WtMol,self.eps,self.Pc,Pamb)
self.CstarODE = isp.calccstar(Gam,self.Tin,self.gas.WtMol)
self.Tc = self.Tin
if self.calcEtaNoz:
if self.isBell:
isConical=0
else:
isConical=1
self.etaBL,self.etaDiv,self.etaKin, etaCf = \
Nozzle_Eff.calcNozzleEfficiency(Pc=self.Pc, Fvac=self.Fvac, eps=self.eps,
epsAtt=self.eps, isConical=isConical, pcentBell=self.pcentBell, halfAngleDeg=self.halfAngDeg,
iprop=self.gasSymbol, mr=1.0, etaKinInp=1.0,
adjBL=1.0, adjKin=1.0, adjDiv=1.0, isRegenCham=0, isRegenNoz=0 )
self.etaNoz = self.etaBL * self.etaDiv # ignore etaKin for now on monoprop
self.effIsp = self.etaCham * self.etaNoz
self.Isp = self.IspODE * self.effIsp
self.Cstar = self.CstarODE * self.etaCham
self.wdotTot = self.Fvac / self.Isp
self.At = self.Cstar* self.wdotTot / self.Pc / Constants.gc
self.Dt = sqrt( self.At / pi ) * 2.0
self.Dcham = self.Dt * sqrt( self.CR )
self.Lcham = self.Dcham * self.LoverDt
self.xlc = self.Lcham / 2.0
self.xln = self.Lcham / 2.0
if self.isBell:
self.Lnoz = (sqrt(self.eps)-1.0)*self.pcentBell*(self.Dt/2.0)/100.0/tan(15.0*pi/180.0)
else:
self.Lnoz = (sqrt(self.eps)-1.0)*(self.Dt/2.0)/tan(self.halfAngDeg*pi/180.0)
self.Dexit = self.Dt * sqrt( self.eps )
self.Lengine = self.Lnoz + self.Lcham + self.Dcham # use Dcham as an inj face fwd length
# start weight calcs
self.wtValve = 0.05 + self.At*100.0
if self.isBell:
self.Lnoz = (sqrt(self.eps)-1.0)*self.pcentBell*(self.Dt/2.0)/100.0/tan(15.0*pi/180.0)
# curve fit of ratio to minimum length rao nozzle
self.ratmlr = (self.pcentBell/100.0) * 1612.1/(self.eps + 1009.0)
self.SAnoz = self.Dt**2/4.*(3.368*(self.eps+10.875)**1.2606 + \
self.eps*(self.ratmlr-1.25)*10.75)
else:
self.Lnoz = (sqrt(self.eps)-1.0)*(self.Dt/2.0)/tan(self.halfAngDeg*pi/180.0)
r1 = self.Dt/2.0
r2 = self.Dexit/2.0
self.SAnoz = pi * sqrt((r1-r2)**2 + self.Lnoz**2) * (r1+r2)
self.thkCham = 0.06 * (self.Pc/1000.0) * (self.Dcham/1.48)
if self.thkCham < self.tmingBody:
self.thkCham = self.tmingBody
self.thkNoz = (self.thkCham*0.9 + 3.5*self.tmingBody) / 4.5
if self.thkNoz < self.tmingBody:
self.thkNoz = self.tmingBody
self.WtNoz = self.thkNoz * self.SAnoz * self.rhoBody
VolChamber = mensuration.cylVol( self.thkCham, self.Dcham, self.xlc ) + \
mensuration.coneVol( self.thkCham, self.Dcham, self.Dt, self.xln )
self.WtChamber = VolChamber * self.rhoBody # chamber is made of same matl as nozzle
self.wtEngine = self.WtChamber + self.WtNoz + self.wtValve
self.mass_lbm = self.Number * self.cxw * self.wtEngine
#END
self.FtoW = self.Fvac * self.Number / self.mass_lbm
def buildSummary(self):
summ = Summary( summName='Cold Gas Thruster',
componentName=self.name, mass_lbm=self.mass_lbm, type=self.type)
summ.addAssumption( 'Propellant : %s (%s)'%(self.gas.name,self.gasSymbol) )
if self.isBell:
summ.addAssumption( 'Bell Nozzle with Percent Bell = %g'%self.pcentBell)
else:
summ.addAssumption( 'Conical Nozzle with Half Angle = %g deg'%self.halfAngDeg )
if self.Number>1:
summ.addAssumption( 'Mass is for %i engines total'%self.Number )
#summ.addInput(self, label='generic param', value=0.0, units='', format='%g')
summ.addInput('Fvac', self.Fvac, 'lbf', '%g')
summ.addInput('Tc', self.Tc, 'degR', '%.1f')
summ.addInput('Pc', self.Pc, 'psia', '%.1f')
summ.addInput('eps', self.eps, '', '%g')
if self.isBell:
summ.addInput('%Bell', self.pcentBell, '%', '%.2f')
else:
summ.addInput('halfAngDeg', self.halfAngDeg, 'deg', '%.2f')
summ.addInput('CR', self.CR, '', '%g')
summ.addInput('LoverDt', self.LoverDt, '', '%g')
summ.addInput('cxw', self.cxw, '', '%g')
summ.addInput('etaCham', self.etaCham, '', '%g')
if not self.calcEtaNoz:
summ.addInput('etaNoz', self.etaNoz, '', '%g')
# outputs
summ.addOutput('Isp', self.Isp, 'sec', '%g')
summ.addOutput('Cstar', self.Cstar, 'ft/sec', '%.1f')
if self.calcEtaNoz:
summ.addOutput('etaBL', self.etaBL, '', '%g')
summ.addOutput('etaDiv', self.etaDiv, '', '%g')
# later... summ.addOutput('etaKin', self.etaKin, '', '%g')
summ.addOutput('etaNoz', self.etaNoz, '', '%g')
summ.addOutput('effIsp', self.effIsp, '', '%g')
summ.addOutput('IspODE', self.IspODE, 'sec', '%g')
summ.addOutput('CstarODE', self.CstarODE, 'ft/sec', '%.1f')
summ.addOutput('Tc', self.Tc, 'degR', '%.1f')
summ.addOutput('wdotTot', self.wdotTot, 'lbm/sec', '%g')
summ.addOutput('At', self.At, 'sqin', '%g')
summ.addOutput('Dt', self.Dt, 'in', '%.3f')
summ.addOutput('Dcham', self.Dcham, 'in', '%.3f')
summ.addOutput('Dexit', self.Dexit, 'in', '%.3f')
summ.addOutput('Lcham', self.Lcham, 'in', '%.3f')
summ.addOutput('Lnoz', self.Lnoz, 'in', '%.3f')
summ.addOutput('Lengine', self.Lengine, 'in', '%.3f')
summ.addOutput('wtValve', self.wtValve, 'lbm', '%.3f')
summ.addOutput('wtEngine', self.wtEngine, 'lbm', '%.3f')
if self.Number>1:
summ.addOutput( 'wt/Assembly', self.mass_lbm/self.Number, 'lbm', '%.3f' )
summ.addOutput('F/W', self.Number * self.Fvac/self.mass_lbm, 'lbf/lbm', '%.3f')
else:
summ.addOutput('F/W', self.Fvac/self.mass_lbm, 'lbf/lbm', '%.3f')
return summ
if __name__ == "__main__": #self test
h = Engine_ColdGas(name="ColdGasEngine", gasSymbol='He',
Tin=400.0,
cxw=1.0, Pc=1000.0, Fvac=0.7, eps=15.0, CR=2.5, LoverDt=4.0,
etaCham=0.97, etaNoz=0.99, isBell=0, pcentBell=100.0,
halfAngDeg=15.0, Number=1, calcEtaNoz=1)
print h.getMassStr()
print
print h.getSummary()
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