set_rocketcea_data_dir(test_dir)
print('ROCKETCEA_DATA_DIR =', get_rocketcea_data_dir())
# compare 200 psia (13.7895 bar) results
C = CEA_Obj(oxName='LOX',
fuelName='LH2',
pressure_units='bar',
cstar_units='m/s',
temperature_units='K',
isp_units='N-s/kg')
IspVac, Cstar, Tcomb = C.get_IvacCstrTc(Pc=13.7895,
MR=1.0,
eps=40.0,
frozen=0,
frozenAtThroat=0)
print('IspVac=%g, Cstar=%g, Tcomb=%g' % (IspVac, Cstar, Tcomb))
print(' .... converted to English ....')
print('IspVac=%g, Cstar=%g, Tcomb=%g' %
(IspVac * 0.101972, Cstar * 3.28084, Tcomb * 1.8))
Cd = CEA_Obj_default(oxName='LOX', fuelName='LH2')
IspVac, Cstar, Tcomb = Cd.get_IvacCstrTc(Pc=200.0,
MR=1.0,
eps=40.0,
frozen=0,
frozenAtThroat=0)
print('IspVac=%g, Cstar=%g, Tcomb=%g' % (IspVac, Cstar, Tcomb))
class HybridCEALookup():
"""
Class to generate and manage N2O-ABS Hybrid engine CEA data for Pc and o/f ratios
"""
__depth = 10
def __init__(self):
self.datapathname = './.lookup.npy'
self.configpathname = './.lookupconfig.json'
self.data = None
self.config = None
self.__loaded = False
# This str provides molecular structure, wt% of fuel, heat of formation, and density information to underlying CEA code
fuel_str = """
fuel ABS(S) C 3.85 H 4.85 N 0.43 wt%=100.0
h,kJ=62.63 t(k)=298.15 rho,kg=1224
"""
add_new_fuel('ABS', fuel_str)
self.cea = CEA_Obj(oxName='N2O',
fuelName='ABS',
cstar_units='m/s',
pressure_units='Pa',
temperature_units='K',
sonic_velocity_units='m/s',
enthalpy_units='J/kg',
density_units='kg/m^3',
specific_heat_units='J/kg-K',
viscosity_units='poise',
thermal_cond_units='W/cm-degC',
make_debug_prints=True)
def generate(self,
pcmin=1,
pcmax=1000,
ofmin=1,
ofmax=40,
pcint=1,
ofint=1):
"""
Generate NxMx8 array of chamber thermodynamic and transport properties from min to max (inclusive).\n
Use CEA to produce the following data at each pc + ofratio combination (8 values)\n
pc : chamber pressure (Pa)\n
of : mixture ratio\n
Tc : chamber temperature (K)\n
k : specific heat ratio\n
MW : molecular weight (g / mol)\n
Pr : Prandtl number\n
Cp : specific heat capacity (J/kg-K)\n
mu : viscocity (poise)\n
cstar : characteristic velocity (m/s)\n
isp : isp (s)
"""
print('Using N2O, ABS, with SI units')
if not self.uses(pcmin=pcmin,
pcmax=pcmax,
pcint=pcint,
ofmin=ofmin,
ofmax=ofmax,
ofint=ofint):
try:
# Construct NxMx8 numpy array to hold all data
xdim, ydim = self.__getDim(pcmin, pcmax, pcint, ofmin, ofmax,
ofint)
data = np.zeros(shape=(xdim, ydim, HybridCEALookup.__depth),
dtype=float)
print(
f'Generating lookup table, {xdim}x{ydim}x{HybridCEALookup.__depth}'
)
# Enumerate over pressure and ofratio ranges and compute CEA results
for (pc_i, pc) in enumerate(np.linspace(pcmin, pcmax, xdim)):
for (of_i,
of) in enumerate(np.linspace(ofmin, ofmax, ydim)):
(cp, mu, _,
pr) = self.cea.get_Chamber_Transport(pc, of)
(mw, k) = self.cea.get_Chamber_MolWt_gamma(pc, of)
(isp, cstar, tc) = self.cea.get_IvacCstrTc(pc, of)
data[pc_i, of_i, :] = np.array(
[pc, of, tc, k, mw, pr, cp, mu, cstar, isp],
dtype=float)
# assign data to obj and save to cache
self.data = data
try:
config = {
"pcmin": pcmin,
"pcmax": pcmax,
"pcint": pcint,
"ofmin": ofmin,
"ofmax": ofmax,
"ofint": ofint,
"pcnum": xdim,
"ofnum": ydim,
"depth": HybridCEALookup.__depth
}
self.config = config
with open(os.path.abspath(self.datapathname), 'wb') as f:
np.save(f, data, allow_pickle=True)
with open(os.path.abspath(self.configpathname), 'w') as f:
json.dump(config, f)
print(
f'Lookup table cached, pcrange: {pcmin}-{pcmax}, ofrange: {ofmin}-{ofmax}'
)
except IOError as ioerror:
print(ioerror)
print("uh oh")
except Exception as exception:
raise exception
else:
print(
f'Using lookup table from cached:\npcrange: {pcmin}-{pcmax}\nofrange: {ofmin}-{ofmax}'
)
def open(self):
"""
Open cached lookup table
"""
try:
with open(os.path.abspath(self.datapathname), 'rb') as f:
self.data = np.load(f, allow_pickle=True)
with open(os.path.abspath(self.configpathname), 'r') as f:
self.config = json.load(f)
self.__loaded = True
return True
except Exception:
# Catch all and return false
return False
def flushCache(self):
"""
"""
try:
with open(os.path.abspath(self.datapathname), 'wb') as f:
np.save(f, [])
with open(os.path.abspath(self.configpathname), 'w') as f:
json.dump({}, f)
except Exception as exception:
print(exception)
def get(self, pc, of):
"""
Retrieve CEA outputs at any chamber pressure
"""
if pc < self.config["pcmin"] or pc > self.config["pcmax"]:
print(
f'Pc: {pc}, Pcmin: {self.config["pcmin"]}, Pcmax: {self.config["pcmax"]}'
)
raise Exception("Chamber pressure out of bounds")
elif of < self.config["ofmin"] or of > self.config["ofmax"]:
print(
f'OF: {of}, OFmin: {self.config["ofmin"]}, OFmax: {self.config["ofmax"]}'
)
raise Exception("OF ratio out of bounds")
# Convert to chamber pressure and OF ratio floating point index
pc_i = (pc - self.config["pcmin"]) / (self.config["pcmax"] -
self.config["pcmin"]) * (
self.config["pcnum"] - 1)
of_i = (of - self.config["ofmin"]) / (self.config["ofmax"] -
self.config["ofmin"]) * (
self.config["ofnum"] - 1)
# Get chamber pressure lower and upper bounds (1d arr)
pc_li = floor(pc_i)
pc_hi = ceil(pc_i)
# OF ratio lower and upper bounds (1d arr)
of_li = floor(of_i)
of_hi = ceil(of_i)
# Get distance of chamber pressure and OF ratio from closest lower index
pc_x = (pc_i - pc_li) # / self.config["pcint"]
of_x = (of_i - of_li) # / self.config["ofint"]
# Interpolate between pressure data
pc_lerp_of_l = self.data[pc_li, of_li, :] + pc_x * (
self.data[pc_hi, of_li, :] - self.data[pc_li, of_li, :])
pc_lerp_of_h = self.data[pc_li, of_hi, :] + pc_x * (
self.data[pc_hi, of_hi, :] - self.data[pc_li, of_hi, :])
# Interpolate between OF ratio data and return result
return pc_lerp_of_l + of_x * (pc_lerp_of_h - pc_lerp_of_l)
def getPc(self, pc):
"""
Return a row vector of OF Ratio results at a provided chamber pressure
"""
if pc < self.config["pcmin"] or pc > self.config["pcmax"]:
raise Exception("Chamber pressure out of bounds")
pc_i = (pc - self.config["pcmin"]) / (self.config["pcmax"] -
self.config["pcmin"]) * (
self.config["pcnum"] - 1)
# Get chamber pressure lower and upper bounds (1d arr)
pc_li = floor(pc_i)
pc_hi = ceil(pc_i)
pc_x = (pc_i - pc_li) # / self.config["pcint"]
return self.data[pc_li, :, :] + pc_x * (self.data[pc_hi, :, :] -
self.data[pc_li, :, :])
def uses(self, pcmin=200, pcmax=800, pcint=10, ofmin=1, ofmax=30, ofint=1):
"""
Check the cached lookup table configuration against specified options\n
"""
if self.__loaded:
xdim, ydim = self.__getDim(pcmin, pcmax, pcint, ofmin, ofmax,
ofint)
useConfig = {
"pcmin": pcmin,
"pcmax": pcmax,
"pcint": pcint,
"ofmin": ofmin,
"ofmax": ofmax,
"ofint": ofint,
"pcnum": xdim,
"ofnum": ydim,
"depth": HybridCEALookup.__depth
}
return useConfig == self.config
return False
def getConfig(self):
"""
Get current lookup table configuration
"""
if self.__loaded:
return self.config
else:
return None
def __getDim(self, pcmin, pcmax, pcint, ofmin, ofmax, ofint):
xdim = ceil((pcmax - pcmin) / pcint) + 1
ydim = ceil((ofmax - ofmin) / ofint) + 1
return xdim, ydim