PHOENICS USER CONFERENCE MOSCOW 2002

1. PHOENICS USER CONFERENCEMOSCOW 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

2. 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

3. 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

4. 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

5. FiatAvio - VEGA

6. 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

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

8. From leaf blowers to rockets

9. 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

10. 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)

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. Plume flowfield

18. Post-processing • PHOENICS data converted into FEMVIEW database using PHIREFLY • FEMVIEW model assembled to provide 3D representation • FEMVIEW LOS and radiation integration routines applied

19. 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

20. LOS – radiation calc

21. 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

22. 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

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

24. 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

25. 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

26. Adverts • User Forum (Thursday) • FEMGV