Transcript PHOENICS USER CONFERENCE MOSCOW 2002

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
– (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 =  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
Adverts
• User Forum (Thursday)
• FEMGV