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 - FiatAvio Introductions - S & C Thermofluids Rocket motor exhaust flowfield modelling Rocket motor exhaust radiative heat transfer VEGA spacecraft Flowfield predictions Radiation predictions Conclusions Recommendations

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

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

FiatAvio - VEGA

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

Methods Build and test - design development systems and fit to experimental rigs Use computer modeling - CFD

From leaf blowers to rockets

Rocket exhaust flow modelling PLUMES 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 Compressible Highly turbulent Heat transfer (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 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

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 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 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

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

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

Plume flowfield

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 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

LOS – radiation calc

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 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

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

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

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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