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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 Limited United Kingdom. Contents. Introductions - F iatAvio Introductions - S & C Thermofluids

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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


Dr. Tony Smith, S & C Thermofluids Limited

United Kingdom


  • 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

F iat avio

  • 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

F iat avio vega
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

F iat avio vega1
FiatAvio - VEGA

S c thermofluids
S & C Thermofluids

  • Formed in 1987

  • Research into fluid (gas/liquid) flow and heat transfer

  • Based in BATH in the West of England


  • Build and test - design development systems and fit to experimental rigs

  • Use computer modeling - CFD

Rocket exhaust flow modelling plumes
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

Rocket motor exhausts
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)

Rocket exhaust modelling
Rocket exhaust modelling


  • 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

Gas radiative heat transfer
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

Vega design calculations
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

Plume prediction
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


  • 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


  • 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

Post processing

  • PHOENICS data converted into FEMVIEW database using PHIREFLY

  • FEMVIEW model assembled to provide 3D representation

  • FEMVIEW LOS and radiation integration routines applied

Radiation calculation
Radiation calculation

  • Based on NASA handbook

  • Nw = ò Nwo (dt(l,w)/dl)dl}

  • Where Nwo is the Planck function for the given wavelength, w, and temperature T

    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.

    t (l,w) = exp [-X(l,w)]

    where the optical depth X is the sum for all radiating species

Radiation calculation1
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

Integration of radiation
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


  • Typically the radiation incident at the surface of the motor was calculated to be around 20kW/m2


  • 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


  • 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


  • User Forum (Thursday)