RocketIsp Code Functions

Thruster

RocketIsp calculates delivered Isp for liquid rocket thrust chambers.

RocketIsp uses a simplified JANNAF approach to calculate delivered specific impulse (Isp) for liquid rocket thrust chambers.

RocketIsp Copyright (C) 2020 Applied Python

This program 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 <http://www.gnu.org/licenses/>.

class rocketisp.rocket_isp.RocketThruster(name='RocketIsp Thruster', coreObj=<rocketisp.stream_tubes.CoreStream object>, injObj=None, noz_regen_eps=1.0, pulse_sec=inf, pulse_quality=0.8, isRegenCham=False, calc_CdThroat=True)

RocketIsp calculates delivered Isp for liquid rocket thrust chambers by simplified JANNAF method.

Parameters:

  • name (str) – name of RocketThruster

  • coreObj (CoreStream) – CoreStream object

  • injObj (Injector) – Injector object (optional)

  • noz_regen_eps (float) – regen cooled nozzle area ratio

  • pulse_sec (float) – s,duration of pulsing engine (default = infinity)

  • pulse_quality (float) – on a scale of 0.0 to 1.0, how good is engine at pulsing

  • isRegenCham (bool) – flag to indicate chamber is regen cooled

  • calc_CdThroat (bool) – flag to trigger calc_CdThroat

Returns:

RocketThruster object

Return type:

RocketThruster

calc_all_eff()

Looks at the efficiency object (effObj) and calculates those efficiencies that have not been set as constants by the user.

see: self.calc_CdThroat or effObj[‘XXX’].is_const for individual efficiencies

get_html_file_str()

return HTML string of the current state of RocketThruster instance.

get_summ_str()

return string of the current state of RocketThruster instance.

reset_attr(name, value, re_evaluate=True)

reset the value of any existing attribute of RocketThruster instance. If re_evaluate is True, then call self.evaluate() after resetting the value of the attribute.

scale_Rt_to_Thrust(ThrustLbf=500.0, Pamb=0.0, use_scipy=False)

Adjust throat size in order to get total thrust at specified ambient pressure exactly

Parameters:

  • ThrustLbf (float) – lbf, desired thrust at specified ambient pressure (Pamb)

  • Pamb (float) – psia, ambient pressure

  • use_scipy (bool) – flag to indicate the need for more sophisticated root finder

Returns:

None

Return type:

None

set_MRthruster(MRthruster=1.6)

Calculate MRcore given desired MRthruster (assume pcentFFC is already set)

set_eff_model(eff_name='Div', model_name='MLP fit')

Change the named efficiency model from the default model to a different model. For example, change from the simple nozzle divergence model (Div) to the Multi-Layer Perceptron (MLP) divergence model.

Parameters:

  • eff_name (str) – name of efficiency (e.g. Div, BL, Kin)

  • model_name (str) – name of model to be used (must be in AVAIL_EFF_MODEL_D)

Returns:

None

Return type:

None

set_eps_to_equal_pexit(Pexit_psia=14.7)

Iterate on Area Ratio to find desired Pexit

set_mr_to_max_ispdel()

Iterate on MRcore to find the peak Isp

summ_print()

print to standard output, the current state of RocketThruster instance.

Geometry

class rocketisp.geometry.Geometry(Rthrt=1, CR=2.5, eps=20, pcentBell=80, LnozInp=None, RupThroat=1.5, RdwnThroat=1.0, RchmConv=1.0, cham_conv_deg=30, LchmOvrDt=3.0, LchmMin=1.0, LchamberInp=None)

The Geometry object holds all the major thrust chamber geometry values.

Parameters:

  • Rthrt (float) – in, throat radius

  • CR (float) – chamber contraction ratio (Ainj / Athroat)

  • eps (float) – nozzle area ratio (Aexit / Athroat)

  • pcentBell (float) – nozzle percent bell (Lnoz / L_15deg_cone)

  • LnozInp (float) – in, user input nozzle length (will override pcentBell)

  • RupThroat (float) – radius of curvature just upstream of throat (Rupstream / Rthrt)

  • RdwnThroat (float) – radius of curvature just downstream of throat (Rdownstream / Rthrt)

  • RchmConv (float) – radius of curvature at start of convergent section (Rconv / Rthrt)

  • cham_conv_deg (float) – deg, half angle of conical convergent section

  • LchmOvrDt (float) – ratio of chamber length to throat diameter (Lcham / Dthrt)

  • LchmMin (float) – in, minimum chamber length (will override LchmOvrDt)

  • LchamberInp (float) – in, user input value of chamber length (will override all other entries)

Returns:

Geometry object

Return type:

Geometry

Variables:

  • At – in**2, throat area

  • Lnoz – in, nozzle length

  • Ltotal – in, nozzle + chamber length

  • Rinj – in, radius of injector

  • Dinj – in, diameter of injector

  • Ainj – in**2, area of injector

  • Lcham_cyl – in, length of cylindrical section of chamber

  • Lcham_conv – in, length of convergent section of chamber

  • Vcham – in**3, approximate chamber volume

LprimeOvRcham()

return chamber length / chamber radius

evaluate()

Uses basic geometry input values to determine derived geometry values. (for example, throat area, nozzle length, injector area, etc.)

getNozObj()

Create and return a Nozzle object.

get_attr_comment(name)

Some attributes may have comments associated with them

get_model_summ_obj()

return ModelSummary object for current state of Geometry instance.

get_summ_str(alpha_ordered=True, numbered=False, add_trailer=True, fillchar='.', max_banner=76, intro_str='')

return string of the current state of Geometry instance.

reset_attr(name, value, re_evaluate=True)

Resets Geometry object attribute by name if that attribute already exists.

summ_print()

print to standard output, the current state of Geometry instance.

rocketisp.geometry.maybe_show_ft(val)

If input inches > 12, return string with feet units.

rocketisp.geometry.solidCylVol(D, L)

calculates a cylinder volume

rocketisp.geometry.solidFrustrumVol(D1, D2, h)

calculates cone frustrum

Nozzle

class rocketisp.nozzle.nozzle.Nozzle(CR=2.5, eps=16.0, pcentBell=80.0, Rt=1.5, Nsegs=20, Rup=2.0, Rd=1.0, cham_conv_ang=30.0, Rc=1.0, theta=None, exitAng=None, forceCone=0, use_huzel_angles=False)

Nozzle contour object holds both a dimensionless and absolute dimension representation of the nozzle. It includes interpolators for entire contour.

Parameters:

  • CR (float) – contraction ratio of chamber (Ainj / Athroat)

  • eps (float) – nozzle area ratio (Aexit / Athroat)

  • pcentBell (float) – nozzle percent bell (Lnoz / L_15deg_cone)

  • Rt (float) – in, throat radius

  • Nsegs (int) – number of segments to hold in array of nozzle contour

  • Rup (float) – radius of curvature just upstream of throat (Rupstream / Rthroat)

  • Rd (float) – radius of curvature just downstream of throat (Rdownstream / Rthroat)

  • cham_conv_ang (float) – deg, half angle of convergent section of chamber

  • Rc (float) – radius of curvature at start of convergent section (Rconvergent / Rthroat)

  • theta (float) – deg, entrance angle of nozzle (tangent to Rd circular curve)

  • exitAng (float) – deg, exit angle of nozzle

  • forceCone (bool) – flag to force nozzle to be a conical nozzle instead of bell nozzle.

  • use_huzel_angles (bool) – flag to force use of Huzel entrance and exit angle correlation

Returns:

Nozzle object

Return type:

Nozzle

get_conv_zL_epsL()

Returns 2 lists for the convergent contour, the z contour and the area ratio contour starting at the injector and going to the throat, but NOT including Throat

get_div_zL_epsL()

Returns 2 lists for the divergent nozzle contour, the z contour and the area ratio contour starting at the throat and going to the nozzle exit, but NOT including Throat

set_abs_Rt(Rt)

Use throat radius to create an absolute contour from the dimensionless contour.

z_range()

return (zmin, zmax)

rocketisp.nozzle.nozzle.ref_nozzle(Rup=2.0, Rd=1.0, eps=16.0, theta=30.0, alphaExit=10.0, pcBell=80.0, Nsegs=30, forceCone=0, cham_conv_ang=30.0, Rc=1.0, CR=2.5)

DIMENSIONLESS Parabolic Nozzle Contour (Rthroat = 1.0)

Efficiencies

class rocketisp.efficiencies.Efficiencies(**constD)

Holds all of the thrust chamber efficiencies and provides access to efficiency models in order to update each one.

evaluate()

Combines nozzle and chamber efficiencies into overall nozzle and over chamber efficiency. Gives overall Isp efficiency including any pulsing effects.

get_model_summ_obj()

return ModelSummary object for current state of Efficiencies instance.

get_state_str_list()

Return a list of | delimited state strings for each Efficiency

get_summ_str()

return string of the current state of Efficiencies instance.

set_const(name, value, re_evaluate=True)

Give a new constant value to named efficiency. Call evaluate if re_evaluate is True.

set_value(name, value, value_src='user input', re_evaluate=True)

Give a new value to named efficiency. Call evaluate if re_evaluate is True.

summ_print()

print to standard output, the current state of Efficiencies instance.

class rocketisp.efficiencies.Efficiency(name, value, desc, value_src)

Holds an individual efficiency that is coordinated by the Efficiencies object.

Parameters:

  • name (str) – name of efficiency (e.g. Div, BL, Kin, etc)

  • value (float) – initial value of efficiency (should be between 0.0 and 1.0)

  • desc (str) – long description of efficiency

  • value_src (str) – technical source of the efficiency (e.g. user input, NASA model, etc.)

Returns:

Efficiency object

Return type:

Efficiency

get_state_str()

Return a | delimited state string.

set_value(value, value_src)

Every time a new value is set, the source of that value must be given.

Stream Tubes

class rocketisp.stream_tubes.BarrierStream(coreObj, pcentFFC=10.0, ko=0.035)

A BarrierStream is typically used to evaluate fuel film cooling, see: https://ntrs.nasa.gov/citations/19770014416 COMBUSTION EFFECTS ON FILM COOLING, 24 Feb 1977 by Aerojet Liquid Rocket Co.

Parameters:

  • coreObj (CoreStream) – core stream tube object, CoreStream

  • pcentFFC (float) – percent fuel film cooling ( FFC flowrate / total fuel flowrate)

  • ko (float) – entrainment constant (typical value is 0.035, range from 0.03 to 0.06)

Returns:

BarrierStream object

Return type:

BarrierStream

Variables:

  • MRbarrier – barrier mixture ratio at throat

  • MRwall – mixture ratio at throat wall

  • Twallgas – degR, temperature of gas at throat wall (cooler upstream)

  • TcODE_b – degR, average ideal ODE temperature of barrier gas

  • WentrOvWcool – ratio of entrained flow rate to FFC flow rate

  • IspDel_b – sec, delivered vacuum barrier Isp

  • IspODF_b – sec, ideal frozen barrier Isp

  • IspODK_b – sec, vacuum kinetic Isp of barrier

  • fracKin_b – fraction of kinetic completion in barrier

  • fracEntr – fraction of core flow entrained into barrier

  • IspODE_b – sec. ideal equilibrium barrier Isp

  • cstarERE_b – ft/s, delivered cstar

  • cstarODE_b – ft/s, ideal equilibrium cstar

evaluate()

Estimate entrained core flow into film cooled stream tube and calculate performance of barrier stream tube.

get_model_summ_obj()

return ModelSummary object for current state of BarrierStream instance.

get_summ_str(alpha_ordered=True, numbered=False, add_trailer=True, fillchar='.', max_banner=76, intro_str='')

return string of the current state of BarrierStream instance.

summ_print()

print to standard output, the current state of BarrierStream instance.

class rocketisp.stream_tubes.CoreStream(geomObj=<rocketisp.geometry.Geometry object>, effObj=<rocketisp.efficiencies.Efficiencies object>, oxName='N2O4', fuelName='MMH', MRcore=1.9, Pc=500, CdThroat=0.995, Pamb=0.0, adjCstarODE=1.0, adjIspIdeal=1.0, pcentFFC=0.0, ko=0.035, ignore_noz_sep=False)

Core stream tube of liquid bipropellant thruster.

Parameters:

  • geomObj (Geometry) – Geometry that describes thruster

  • effObj (Efficiencies) – Efficiencies object to hold individual efficiencies

  • oxName (str) – name of oxidizer (e.g. N2O4, LOX)

  • fuelName (str) – name of fuel (e.g. MMH, LH2)

  • MRcore (float) – mixture ratio of core flow (ox flow rate / fuel flow rate)

  • Pc (float) – psia, chamber pressure

  • CdThroat (float) – Cd of throat (RocketThruster object may override)

  • Pamb (float) – psia, ambient pressure (for example sea level is 14.7 psia)

  • adjCstarODE (float) – multiplier on NASA CEA code value of cstar ODE (default is 1.0)

  • adjIspIdeal (float) – multiplier on NASA CEA code value of Isp ODE (default is 1.0)

  • pcentFFC (float) – percent fuel film cooling (if > 0 then add BarrierStream)

  • ko (float) – entrainment constant (passed to BarrierStream object, range from 0.03 to 0.06)

  • ignore_noz_sep (bool) – flag to force nozzle flow separation to be ignored (USE WITH CAUTION)

Returns:

CoreStream object

Return type:

CoreStream

Variables:

  • FvacTotal – lbf, total vacuum thrust

  • FvacCore – lbf, vacuum thrust due to core stream tube

  • MRthruster – total thruster mixture ratio’)

  • IspDel – sec, <=== thruster delivered vacuum Isp ===>

  • Pexit – psia, nozzle exit pressure

  • IspDel_core – sec, delivered Isp of core stream tube

  • IspODF – sec, core frozen Isp

  • IspODK – sec, core one dimensional kinetic Isp

  • IspODE – sec, core one dimensional equilibrium Isp

  • cstarERE – ft/s, delivered core cstar

  • cstarODE – ft/s, core ideal cstar

  • CfVacIdeal – ideal vacuum thrust coefficient

  • CfVacDel – delivered vacuum thrust coefficient

  • CfAmbDel – delivered ambient thrust coefficient

  • wdotTot – lbm/s, total propellant flow rate (ox+fuel)

  • wdotOx – lbm/s, total oxidizer flow rate

  • wdotFl – lbm/s, total fuel flow rate

  • TcODE – degR, ideal core gas temperature

  • MWchm – g/gmole, core gas molecular weight

  • gammaChm – core gas ratio of specific heats (Cp/Cv)

calc_cea_perf_params()

Calc basic Isp values from CEA and calc implied IspODK from current effKin value.

evaluate()

Assume that all efficiencies have been set, either by original user value or an update by an efficiency model.

get_model_summ_obj()

return ModelSummary object for current state of CoreStream instance.

get_summ_str(alpha_ordered=True, numbered=False, add_trailer=True, fillchar='.', max_banner=76, intro_str='')

return string of the current state of CoreStream instance.

reset_CdThroat(value, method_name='RocketIsp', re_evaluate=True)

reset the value of CdThroat If re_evaluate is True, then call self.evaluate() after resetting the efficiency.

reset_attr(name, value, re_evaluate=True)

reset the value of any existing attribute of CoreStream instance. If re_evaluate is True, then call self.evaluate() after resetting the value of the attribute.

summ_print()

print to standard output, the current state of CoreStream instance.

rocketisp.stream_tubes.shapeFactor(WentrOvWcool)

Subsonic Shape Factor from COMBUSTION EFFECTS ON FILM COOLING manual Figure 5, page 88 https://ntrs.nasa.gov/citations/19770014416 “Mixing Layer Profile Shape Factor Correlations”

rocketisp.stream_tubes.solve_At_split(MRc, MRb, ffc, cstar_c, cstar_b)

Given MRcore, MRbarrier, fracFFC, cstar_c and cstar_b, solve the throat area split between the core and barrier.

Injector

class rocketisp.injector.Injector(coreObj, Tox=None, Tfuel=None, elemEm=0.8, fdPinjOx=0.25, fdPinjFuel=0.25, dpOxInp=None, dpFuelInp=None, setNelementsBy='acoustics', elemDensInp=5, NelementsInp=100, OxOrfPerEl=1.0, FuelOrfPerEl=1.0, lolFuelElem=False, setAcousticFreqBy='mode', desAcousMode='3T', desFreqInp=5000, CdOxOrf=0.75, CdFuelOrf=0.75, dropCorrOx=0.33, dropCorrFuel=0.33, DorfMin=0.008, LfanOvDorfOx=20.0, LfanOvDorfFuel=20.0)

Injector object holds basic information about the injector. Injector design features are calculated including chamber losses due to the injector, Em, Mix and Vap.

Parameters:

  • coreObj (CoreStream) – CoreStream object

  • Tox (None or float) – degR, temperature of oxidizer

  • Tfuel (None or float) – degR, temperature of fuel

  • elemEm (float) – intra-element Rupe mixing factor (0.7 below ave, 0.8 ave, 0.9 above ave)

  • fdPinjOx (float) – fraction of Pc used as oxidizer injector pressure drop

  • fdPinjFuel (float) – fraction of Pc used as fuel injector pressure drop

  • dpOxInp (None or float) – psia,input value of injector pressure drop for oxidizer (overrides fdPinjOx)

  • dpFuelInp (None or float) – psia,input value of injector pressure drop for fuel (overrides fdPinjFuel)

  • setNelementsBy (str) – flag determines how to calculate number of elements ( “acoustics”, “elem_density”, “input”)

  • elemDensInp (float) – elem/in**2, input value for element density (setNelementsBy == “elem_density”)

  • NelementsInp (float) – input value for number of elements (setNelementsBy == “input”)

  • OxOrfPerEl (float) – number of oxidizer orifices per element

  • FuelOrfPerEl (float) – number of fuel orifices per element

  • lolFuelElem (bool) – flag for like-on-like fuel element (determines strouhal multiplier)

  • setAcousticFreqBy (str) – flag indicating how to determine design frequency. (can be “mode” or “freq”)

  • desAcousMode (str or float) – driving acoustic mode of injector OR acoustic mode multiplier (setNelementsBy==”acoustics” and setAcousticFreqBy==”mode”)

  • desFreqInp (None or float) – Hz, driving acoustic frequency of injector (sets D/V if setNelementsBy==”acoustics” and setAcousticFreqBy==”freq”)

  • CdOxOrf (float) – flow coefficient of oxidizer orifices

  • CdFuelOrf (float) – flow coefficient of fuel orifices

  • dropCorrOx (float) – oxidizer drop size multiplier (showerhead=3.0, like-doublet=1.0, vortex=0.5, unlike-doublet=0.33)

  • dropCorrFuel (float) – fuel drop size multiplier (showerhead=3.0, like-doublet=1.0, vortex=0.5, unlike-doublet=0.33)

  • DorfMin (float) – in, minimum orifice diameter (lower limit)

  • LfanOvDorfOx (float) – fan length / oxidizer orifice diameter

  • LfanOvDorfFuel (float) – fan length / fuel orifice diameter

Returns:

Injector object

Return type:

Injector

Variables:

  • sgOx – g/ml, oxidizer density

  • dHvapOx – BTU/lbm, oxidizer heat of vaporization

  • surfOx – lbf/in, oxidizer surface tension

  • viscOx – poise, oxidizer viscosity

  • MolWtOx – g/gmole, oxidizer molecular weight

  • sgFuel – g/ml, fuel density

  • dHvapFuel – BTU/lbm, fuel heat of vaporization

  • surfFuel – lbf/in, fuel surface tension

  • viscFuel – poise, fuel viscosity

  • MolWtFuel – g/gmole, fuel molecular weight

  • dpOx – psid, oxidizer injector pressure drop

  • dpFuel – psid, fuel injector pressure drop

  • des_freq – Hz, chamber design acoustic frequency

  • DorfFlForHzLimit – in, fuel orifice Diameter for frequency in Hewitt Correlation

  • Nelements – number of elements on injector face

  • NFuelOrf – number of fuel orifices on injector face

  • NOxOrf – number of oxidizer orifices on injector face

  • elemDensCalc – elem/in**2, element density on injector face

  • NelemMakable – maximum number of makable elements giving correct flow rate (diam=DorfMin)

  • velOx_fps – ft/s, velocity of injected oxidizer

  • velFuel_fps – ft/s, velocity of injected fuel

  • AfloOx – in**2, total flow area of oxidizer

  • AfloFuel – in**2, total flow area of fuel

  • DorfOx – in, oxidizer orifice diameter

  • DorfFuel – in, fuel orifice diameter

calc_element_attr()

calc Nelements, injection velocities, elements diam, etc.

calculate_effEm()

calc intra-element mixing efficiency

calculate_effMix()

calc inter-element mixing efficiency

calculate_effVap()

calculate vaporization efficiency

evaluate(DOREVAL=False)

Calculates chamber losses due to the injector, Em, Mix and Vap.

get_closest_mode()

Get the name and frequency of the closest mode to des_freq

get_model_summ_obj()

return ModelSummary object for current state of Injector instance.

get_summ_str(show_core_stream=True, alpha_ordered=True, numbered=False, add_trailer=True, fillchar='.', max_banner=76, intro_str='')

return string of the current state of Injector instance.

summ_print(show_core_stream=True)

print to standard output, the current state of Injector instance.

rocketisp.injector.temperature_clamp(value, name, min_value, max_value)

Check to see if name is limited in range.