Challenges in GT CFD - Lapworth - RR Lec 2008

7/28/2019 Challenges in GT CFD - Lapworth - RR Lec 2008

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2008 Rolls-Royce plc

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its subsidiary or associated companies.

Title - Arial 28ptThe Challenges for Aero-EngineCFD

Leigh Lapworth,

Rolls-Royce plc.,

Derby, UK.


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

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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 thesegenerates 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 persecond 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 been

accelerated to a speed of 1050 miles per hour.l Fuel burns in the Trent engine's combustion chamber at temperatures up to

2,000C, which is well above the 1,300C 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 330

passengers 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 1,000

miles per hour.

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


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Civil Aerospace Drivers

lThe ACARE* Environmental Goals for 2020l Background:

l In 2000, the European Union Commissioner Philippe Busquin asked a

distinguished group of representatives from the European aviation industries

to 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 Goals

l 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.


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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 of

innovative new concepts.

CCAEP = Committee on Aviation Environmental Protection


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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 efficiency

l Lower design cruise speed to reduce

drag and a shorter design range to

reduce weight

l Noise reductions from shielding and

subsonic 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 CambridgeMIT-Institute with

industrial supportl A noise of 63 dBA outside airport

perimeter. This is some 25dB

quieter 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 operability

l Adjacent rows of rotating and stationary blades,

l Inherently unsteady flow field,

l Transitional and turbulent flow fields with complicated secondary flows andleakage 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 CFD

l 1992: Denton - steady mixing planes using circumferential averagingl 1985: Adamcyzk passage averaging and deterministic stresses

l 1995: Le Jambre overlapping meshes and networked workstations

l Unsteady Multistage CFDl 1996: Denton simple H-meshes with sliding planes between blade rows

l 1992: Giles linear unsteady single blade row with prescribed unsteady b.c.s

l 1993: Dawes unstructured meshes with spatial & temporal adaptation

l 1998: He Multistage with phase lagging to reduce blade countsl 2000: Hall Multi-frequency linear analysis using harmonic balance

l 2005: Vahdati Whole annulus 17 blade row compressor simulation

l 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 space

l 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

sureRiseCoefficient,

60

65

70

75

80

85

90

Efficiency,

EXPUNSTEADY

STEADYEXPUNSTEADYSTEADY

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 research

compressor


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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,

l Mixing and sliding planes for turbomachinery,

l 1 and 2 equation turbulence models, transition and LES capability,

l Moving mesh,

l Linearised unsteady and adjoint CFD capabilities

l Development network

l 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 tunnel

l Mesh generated by PADRAM extending to large radius, typically 4-5 rotor

heights.

l CFD simulations using HYDRA

l Simulations performed at the Whittle Laboratory (Hall & Zachariadis)


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Rig 140

(Zachariadis & Hall, Cambridge University)

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

0.5550.531Overall Propulsive

Efficiency (?)

HYDRARIG DATA0.7260.733Overall Propulsive

Efficiency (?)

HYDRARIG DATA


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Ground Effects

l Engines on the ground can

ingest a ground vortex

l Can influence engine operability,

l CFD used to design intake lines to

meet operability criteria

l CFD also used for crosswind and

incidence effects

HYDRA simulation (West, RR)


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Design Using Adjoint CFD

l Engine Section Stator optimisation

l 86 design parameters skew, lean, sweep, LE & TE recamber and endwallprofiling

l 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 is

decomposed into radial modes.

CAA applied as a transfer

function.

Coupling CFD & CAA for Noise

CAA used to compute sound

pressure level (SPL) on fuselage

exterior.

Used to estimate cabin noise

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


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l Blades skewed individually to match

measured blade tip stagger angles

Surface static pressure

HYDRA Buzz-Saw Noise

Full Annulus CFD solution

l Non-Linear HYDRA

l Complex geometry (eg tip gap)

l

Includes intake acoustic linerl 55 Million nodes

l 40 dual processor PC cluster nodes

l 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 exterior

measurements

Engine Order

SPL

[dB]

0 10 20 30 40 50 60

Measurement Predic tion

10dB



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Cooling the Turbine

l Turbine entry temperatures (TET) are well above the melting point of the metal

l RB211-22C (1971) TET=1500K, Trent 800 (1996) TET>1800K

l Higher TET increases the propulsive efficiency of the engine

l Turbine is cooled via

l Thermal barrier coating

l Film cooling

l 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 vectored

downwards, 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 directions

l High geometric and physical fidelity

l Increasing use of unsteady CFD and

LES

l Component coupling, leading to:

l System level design optimisation

l Virtual engine simulations

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

blades

LES simulation of a fan rotor for

broadband noise (Ray, Cambridge)

LES simulation of compressor

stator (McMullan, Loughborough)

Whole Engine CFD (e.g. Stanford)

Challenges in GT CFD - Lapworth - RR Lec 2008

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