TiThtlee Ch- Arialallenges 28pt for Aero-Engine CFD · TiThtlee Ch- Arialallenges 28pt for...

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Title - Arial 28ptThe Challenges for Aero-EngineCFD

Leigh Lapworth,Rolls-Royce plc.,

Derby, UK.

ICFD 25th Anniversary Meeting, 15-16 September, 2008

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© 2008 Rolls-Royce plc

The Product

Trent 800 on Singapore Airlines Boeing 777

Trent 900 cutaway (powers Airbus A380)


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Some Facts and Figures*l The power a Trent engine generates at take off is about 90,000 horsepower -

equivalent to the power of 1,200 family-sized cars.l There are 92 high pressure turbine blades in a Trent 800 engine. Each of these

generates about 800 horsepower - equivalent to a Formula 1 racing car.l While generating its 92,000lb thrust, the Trent sucks in more than 1 ton of air per

second at about 350 miles per hour. Equivalent to emptying a squash court of airin less than one second.

l By the time the air leaves the nozzle at the back of the engine, it has beenaccelerated to a speed of 1050 miles per hour.

l Fuel burns in the Trent engine's combustion chamber at temperatures up to2,000°C, which is well above the 1,300°C at which some component metals usedwould start to melt.

l The heat transfer rate achieved by the cooling air system in each High PressureTurbine blade is equivalent to a domestic central-heating boiler or air-conditioningunit.

l The Boeing 777, which is powered by two Trent 800 engines, carries around 330passengers and gives about 120 passenger-miles to the gallon.

l The tip speed of the Trent fan blades and first stage turbine blades is over 1,000miles per hour.

* http://www.rolls-royce.com/education/schools/facts/default.jsp

http://www.rolls-


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Civil Aerospace DriverslThe ACARE* Environmental Goals for 2020l Background:

l In 2000, the European Union Commissioner Philippe Busquin asked adistinguished group of representatives from the European aviation industriesto set out their vision for the future of aviation in the medium and long term.

l ACARE was set up with the objective of realising the goals.l In 2002 the Strategic Research Agenda was published which set out four

goals aimed at meeting the environmental challenge for 2020.

l The Goalsl To reduce fuel consumption and CO2 emissions by 50 per cent,l To reduce perceived external noise by 50 per cent,l To reduce NOx by 80 per cent,l To make substantial progress in reducing the environmental impact of the

manufacture, maintenance and disposal of aircraft and related products.

* Advisory Council for Aeronautical Research in Europe


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The ACARE Challenge

* http://www.rolls-royce.com/rolls-royce-environment/reducing-en-impact/aviation.html

Reductions in emissions from aviation can be gained from three main sources:

Target: Airframe plus Engine plus Operations can deliver 50 per cent reduction inCO2 emissions per passenger kilometre.

http://www.rolls-


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The ACARE Challenge

* http://www.rolls-royce.com/rolls-royce-environment/reducing-en-impact/aviation.html

Nox and Noise reductions remain difficult goals to achieve – leading a range ofinnovative new concepts.

CCAEP = Committee on Aviation Environmental Protection

http://www.rolls-


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Radical new concepts

*http://www.easyjet.com/en/news/easyjet_ecojet.html,Photograph: Frank Baron

l easyJet ecoJet*l Target EIS in 2015, concepts:l Rear mounted open-rotor engine with

high propulsive efficiencyl Lower design cruise speed to reduce

drag and a shorter design range toreduce weight

l Noise reductions from shielding andsubsonic rotor tip speeds (via gearbox)

l New light-weight materials

**http://silentaircraft.org/

l Silent Aircraft Initiative**l Target EIS in 2030 onwards,l SAX-40 concept aircraft designed

by Cambridge– MIT-Institute withindustrial support

l A noise of 63 dBA outside airportperimeter. This is some 25dBquieter than current aircraft


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The Challenge of Turbomachinery

l Aerodynamic performance of the turbomachinery is the criticalfactor in engine efficiency, thrust and operabilityl Adjacent rows of rotating and stationary blades,l Inherently unsteady flow field,l Transitional and turbulent flow fields with complicated secondary flows and

leakage effects.l Stringent levels of conservation needed


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25 years of Turbomachinery CFDl Turbomachinery CFD has a long pedigree:

l 1952: C-H Wu - S1-S2 stream surface method– Coupled through-flow and blade-to-blade CFD - still mainstay of design

l 1979: Denton - single blade row CFD based on sheared H-meshes and finitevolume time-marching scheme

l 1983: Single blade row CFD using single block meshes and simple mixinglength turbulence models. Bespoke and academic codes

l Steady Multistage CFDl 1992: Denton - steady mixing planes using circumferential averagingl 1985: Adamcyzk – passage averaging and deterministic stressesl 1995: Le Jambre – overlapping meshes and networked workstations

l Unsteady Multistage CFDl 1996: Denton – simple H-meshes with sliding planes between blade rowsl 1992: Giles – linear unsteady single blade row with prescribed unsteady b.c.sl 1993: Dawes – unstructured meshes with spatial & temporal adaptationl 1998: He – Multistage with phase lagging to reduce blade countsl 2000: Hall – Multi-frequency linear analysis using harmonic balancel 2005: Vahdati – Whole annulus 17 blade row compressor simulationl 2006: Schluter – 20o sector of whole engine including LES of combustor


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Multistage Design by CFDl Multistage CFD allows

compressors to exploit the 3Daerodynamic design spacel Unsophisticated sheared H-mesh codes

with mixing planes,l 3D blading gives better efficiency and

stall range enabling:l Lower blade counts and higher loadingsTrent 900 datum compressor at design point

Trent 900 3D re-design at design point

red regions indicate flow separation

2D design

3D design


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0.1

0.2

0.3

0.4

0.5

0.6

0.38 0.43 0.48 0.53 0.58

Vx/Umid

Pres

sure

Ris

e C

oeff

icie

nt, ψ

60

65

70

75

80

85

90

Effic

ienc

y, η

EXPUNSTEADYSTEADYEXPUNSTEADYSTEADY

Simulating Operability

HYDRA simulation (Montomoli, Cambridge U)

l Simulating the stability boundary:l Steady multistage CFD performs well at the design point, but cannot predict

stability boundary where wakes and corner separations are morepronounced leading to higher levels of blade row interaction

l Unsteady multistage CFD with sliding planes performs much better near thestall boundary.

4 stage researchcompressor


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HYDRA CFD Solverl HYDRA

l Hybrid unstructured CFD capability,l Parallel on shared and distributed memory machines,l Convergence acceleration using pre-conditioning and multigrid,l Steady and unsteady flow,lMixing and sliding planes for turbomachinery,l 1 and 2 equation turbulence models, transition and LES capability,lMoving mesh,l Linearised unsteady and adjoint CFD capabilities

l Development networkl Initial code developed by Prof. Mike Giles at Oxford UTC in CFD,l Ongoing development by Aerothermal Methods Group and network of

UTCs– Oxford, Cambridge, Loughborough, Surrey, DLR, etc.


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HYDRA Applications

Fans

Turbines

Installations

NoiseExhausts

Full aircraft

Energy

Compressors

Air Systems


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Improving Efficiency, Reducing SFC


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Open Rotor Simulations

l Open rotor rig 140 tested in ARA wind tunnellMesh generated by PADRAM extending to large radius, typically 4-5 rotor

heights.l CFD simulations using HYDRAl Simulations performed at the Whittle Laboratory (Hall & Zachariadis)


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Rig 140

(Zachariadis & Hall, Cambridge University)

Cruise Conditions (M8 = 0.75)Take-Off Conditions (M8 = 0.20)

0.5550.531Overall PropulsiveEfficiency (?)

HYDRARIG DATA

0.7260.733Overall PropulsiveEfficiency (?)

HYDRARIG DATA


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Ground Effects

l Engines on the ground caningest a ground vortexl Can influence engine operability,l CFD used to design intake lines to

meet operability criterial CFD also used for crosswind and

incidence effects

HYDRA simulation (West, RR)


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Design Using Adjoint CFD

l Engine Section Stator optimisationl 86 design parameters – skew, lean, sweep, LE & TE recamber and endwall

profilingl Unconstrained SQP optimisation using adjoint gradients from HYDRA

(Duta, Oxford University)


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ESS Optimisation Using Adjoint CFD

OptimumOriginal

Contours of axial velocity near ESS Trailing Edge (Duta, Oxford University)


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CFDCAAFan

U

S

Intake Liner

CFD Solution at plane U isdecomposed into radial modes.

CAA applied as a transferfunction.

Coupling CFD & CAA for Noise

CAA used to compute soundpressure level (SPL) on fuselageexterior.

Used to estimate cabin noise

CFD/CAA Simulation (RR & Boeing, AIAA 2007-3517)


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l Blades skewed individually to matchmeasured blade tip stagger angles

Surface static pressure

HYDRA Buzz-Saw Noise

Full Annulus CFD solutionl Non-Linear HYDRAl Complex geometry (eg tip gap)l Includes intake acoustic linerl 55 Million nodesl 40 dual processor PC cluster nodesl 4-5 days run time using multi-grid

CAA solution (HYDRA Linearised Euler)



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Buzz-saw source radiation andtransmission into Cabin

CFD + CAA transmission Characteristics calibrated against exteriormeasurements

Engine Order

SP

L [d

B]

0 10 20 30 40 50 60

Measurement Prediction

10dB



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Combustion CFD modellingl Prediction targets:

l Combustor internal flows:– Velocities, temperatures, pressures and emissions at

both steady and unsteady state conditionsl Diffuser flow and external aerodynamics:

– Velocity profiles and pressure lossl Flows for small-scale components:

– Fuel injectors– Cooling devices– Port flows

l Metal temperatures:– Boundary conditions for thermal analysis

l Main challenges:l Fluid mechanics:

– Recirculations, high turbulence, complex geometryl Two-phase flows:

– Liquid fuel modellingl Combustion:

– Varying fuel properties, chemistry-turbulenceinteraction

l Heat transfer:– Radiation and convection to walls

l Pollutant formation:– NOx, smoke, CO, UHC

geometry

mesh

solution


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Cooling the Turbine

l Turbine entry temperatures (TET) are well above the melting point of the metall RB211-22C (1971) TET=1500K, Trent 800 (1996) TET>1800K

l Higher TET increases the propulsive efficiency of the enginel Turbine is cooled via

l Thermal barrier coatingl Film coolingl Conduction from internal cooling passages which feed film cooling holes


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Hot Gas Ingestion Modelling

l On vertical take-off/landing aircraft (Harrier, JSF), when the engines are vectoreddownwards, it is possible for the hot exhaust gases to re-enter the engine intakel This is a potential source of engine stall

l HYDRA CFD simulations are being used in place of wind tunnel tests.(Ricardson, Cambridge University)


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Hot Gas Ingestion Modelling

HYDRA simulation – contours of temperatureExperimental facility(Ricardson, Cambridge University)


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Future directionsl High geometric and physical fidelity

l Increasing use of unsteady CFD andLES

l Component coupling, leading to:l System level design optimisationl Virtual engine simulations

l Continued use of HPCl E.g. Trent engines have O(5000)

blades

LES simulation of a fan rotor forbroadband noise (Ray, Cambridge)

LES simulation of compressorstator (McMullan, Loughborough)

Whole Engine CFD (e.g. Stanford)

TiThtlee Ch- Arialallenges 28pt for Aero-Engine CFD · TiThtlee Ch- Arialallenges 28pt for...

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