1. 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

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

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 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

10. 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)

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

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