phoenics user conference moscow 2002 the problem of exhaust plume radiation during the launch phase...
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PHOENICS USER CONFERENCE
MOSCOW 2002
The problem of exhaust plume radiation during the launch
phase of a spacecraft
Attilio Cretella, FiatAvio, Italy and
Dr. Tony Smith, S & C Thermofluids LimitedUnited Kingdom
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Contents
• Introductions - FiatAvio • Introductions - S & C Thermofluids• Rocket motor exhaust flowfield modelling• Rocket motor exhaust radiative heat transfer• VEGA spacecraft • Flowfield predictions • Radiation predictions • Conclusions• Recommendations
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FiatAvio
• Aerospace design and manufacturing company
• Responsibility for the supply of the loaded cases of the solid rocket boosters on the Ariane V launcher (thermal protection and grain design) and the performance of the boosters
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FiatAvio - VEGA
• 4 stage launcher for 1500Kg payload in 700Km circular polar orbit
• 1st, 2nd and 3rd stage with solid propellant motors of 80, 23 and 9 tons thrust respectively using filament wound carbon fibre casings
• 4 stage - liquid propellant motor
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FiatAvio - VEGA
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S & C Thermofluids
• Formed in 1987
• Research into fluid (gas/liquid) flow and heat transfer
• Based in BATH in the West of England
www.thermofluids.co.uk
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Methods
• Build and test - design development systems and fit to experimental rigs
• Use computer modeling - CFD
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From leaf blowers to rockets
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Rocket exhaust flow modellingPLUMES
• flowfield prediction
• 2- or 3-d compressible flows with multi-species chemical reaction
• rocket motor, gas-turbine and diesel engine exhausts
• large chemical species and reaction database
• single or multiple plumes, nozzles and ejectors
• plume interaction with vehicle and free stream
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Rocket motor exhausts
• Compressible – (high pressures, temperatures - typical exit Mach
number is around 2.5)
• Highly turbulent• Heat transfer • Chemical transport and reaction • Multiphase • 2D axisymmetric and sometimes 3D (even if
only through swirl)
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Rocket exhaust modelling
• CFD - PHOENICS
• PLUMES code considers flow through nozzles and out into surroundings
• Chemical transport and reaction included
• Input is in terms of chamber pressure, temperature and species concentrations
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Gas radiative heat transfer
• Based on FEMVIEW post-processor• Lines of sight (LOS) sent from view position out
towards source - plume• Intersection with model elements (cells)
provided by FEMVIEW • Using element data and order, radiation
emission and absorption is calculated taking account of chemical composition and particles
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VEGA design calculations
• 3rd stage is used at high altitude >100km
• The exhaust plume is highly underexpanded (50 bar chamber pressure)
• Plume quite visible from the surface of the motor
• The plume contains a high concentration of aluminium oxide (AL2O3) particles (liquid and solid) and so surface radiation must be evaluated
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PLUME prediction
• PLUMES code used - continuum assumed• Axisymmetric, 2D - polar mesh• Progressive reduction in ambient pressure
and change in domain size (but not grid) to achieve very difficult convergence
• Free stream set to zero• No reactions (low O2 concentrations)• Single phase - assumes AL2O3 follows gas
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SATELLITE
• Solution of P1, V1,W1, H1 and species concentrations as required
• Turbulence solution is initiated (normally k-e)
• Grid details
• Nozzle mass flux and free stream boundary conditions
• Global source terms for chemical reactions
• Initial field values
• Under-relaxation levels
• Property settings
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EARTH
• Cp function of gas composition and temperature.
• Density - ideal gas equation using mean molecular weight based on local species concentration
• Source terms for reacting chemical species concentrations based on Arrhenius rate expressions.
• Static temperature derived using stagnation enthalpy, kinetic energy (U2) and Cp
• Elemental mass balance for chemical species
• Calculation and output of additional parameters, including Mach number and thrust/specific impulse
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Plume flowfield
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Post-processing
• PHOENICS data converted into FEMVIEW database using PHIREFLY
• FEMVIEW model assembled to provide 3D representation
• FEMVIEW LOS and radiation integration routines applied
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Radiation calculation
• Based on NASA handbook • N = N
o (d(l,)/dl)dl}• Where N
o is the Planck function for the given wavelength, , and temperature T
is the transmissivity of the gas at a given location and is in turn a function of wavelength and path length, l, along the line of sight.
(l,) = exp [-X(l,)] where the optical depth X is the sum for all radiating
species
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LOS – radiation calc
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Radiation calculation
• The optical depth was calculated based on local path length and absorption for CO2, CO, H2O and particles.
• Because no data was available for AL2O3 absorption, data for particles of similar emissivity was used
• A wide bandwidth was used to capture all of the incident energy
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Integration of radiation
• Normally an array parallel lines of sight are sent out from the view at the surface integral is taken
• The plume is effectively too close to the motor surface to do this.
• Individual lines of sight were sent out at different angles and then these values were integrated taking account the angle of incident radiation
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Results
• Typically the radiation incident at the surface of the motor was calculated to be around 20kW/m2
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CONCLUSIONS
• The amount of radiation incident upon the surface of a launch vehicle has been calculated
• The flowfield was predicted using the PLUMES software which uses the PHOENICS CFD solver at its core
• By assembling the 2D CFD results into a FEMVIEW 3D model, the radiative heat transfer could be calculated by integrating the transmission along a line of sight through the plume from the surface of the launcher
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RECOMMENDATIONS
• Efforts need to made to validate the approach used
• The following areas need to be addressed– Assumption of continuum at these altitude– Plume structure at these pressure ratios– Al2O3 absorption coefficients– Radiation calculation method
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