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

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 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

• 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

• 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 • 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

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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