Technical Memorandum 105613

E^^9y3

The Future Challenge for Aeropropulsion

Robert RosenNational Aeronautics and Space AdministrationWashington, DC

and

David N. BowditchLewis Research CenterCleveland, Ohio

Prepared forAeroengine 92Moscow, Russia, April 6-12, 1992

NASA

https://ntrs.nasa.gov/search.jsp?R=19920015921 2020-02-23T06:19:29+00:00Z

THE FUTURE CHALLENGE FOR AEROPROPULSION

by

Dr. Robert RosenDeputy Associate Administrator

Office of Aeronautics and Space TechnologyNASA Headquarters

and

David N. BowditchChief Technologist, Aeronautics Directorate

NASA Lewis Research Center

Abstract

NASA's research in aeropropulsion isfocused on improving the efficiency,capability, and environmental compati -bility for all classes of future air-craft. The development of innovativeconcepts, physical understanding andtheoretical, experimental and computa-tional tools provide the knowledge basefor continued propulsion system advanc-es. Key fundamental enabling technolo-gies include advances in internal fluidmechanics, structures, light-weighthigh-strength composite materials, andadvanced sensors and controls. Recentemphasis has been on the development ofadvanced computational tools in internalfluid mechanics, structural mechanics,reacting flows, and computational chem-istry. The improved computational capa-bility and advanced materials are beingused to develop advanced propulsionsystem component technology, for exam-ple., lightweight turbomachinery withimproved efficiency, combustor systemsthat retain high combustion efficiencywhile reducing harmful emissions, andlow noise, lightweight exhaust systems.The fundamental knowledge base and com-ponent technology form the physical andanalytical foundation for focused re-search activities. For subsonic trans-port applications, very high bypassratio turbofans with increased enginepressure ratio are being investigated to

increase fuel efficiency and reduce air-port noise levels. In a joint superson-ic cruise propulsion program with indus-try, the critical environmental concernsof emissions and community noise arebeing addressed. NASA is also providingkey technologies for the National Aero-spaceplane, and is studying propulsionsystems that provide the capability foraircraft to accelerate to and cruise inthe Mach 4-6 speed range. The combina-tion of fundamental, component and fo-cused technology development underway atNASA will make possible dramatic advanc-es in aeropropulsion efficiency andenvironmental compatibility for futureaeronautical vehicles.

Introduction

NASA is pioneering a broad fundamentalknowledge and technology base that iscritical to the design of advanced aero-nautical systems, both civil and mili-tary. We are pursuing the developmentof innovative concepts, the physicalunderstanding and the theoretical, ex-perimental and computational tools thatprovide the foundation to keep the Unit-ed States at the forefront of aviation.This knowledge base forms the physicaland analytical foundation for NASA'scurrent and future focused researchactivities as well as the understandingrequired for concept breakthroughs. Theexpertise of its researchers and its

figure. The upper portion of the figureillustrates the formation of the leakagevortex and its encounter with the in-passage shock at the near stall operat-ing condition. The views in all por-tions of the figure are from the shroudlooking in toward the hub. The lowerleft portion of the figure shows thestreamlines at 99% span as defined byparticle paths originating upstream ofthe rotor at a radial surface above therotor tip. The streamline originatingfrom the leading edge divides the up-stream flow from that which came throughthe clearance. The shock location isalso shown in this figure. The lowercenter portion of the figure shows thepaths of fluid particles released in theclearance region over the suction sur-face. The line 0-P shows the trajectoryof the vortex across the passage. Theformation of the leakage vortex is evi-dent. The vortex cross section increas-es markedly in size as it traverses theshock. This vortex growth is responsi-

SHOCK

KKONT

FLOW

e-

Oy

O

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r'0

IFaM;

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experimental and computational facili-ties place NASA in a position to performthe broad range of disciplinary andapplied research needed in the future.

Critical Disciplines

The basic aeropropulsion disciplinetechnologies include internal fluidmechanics, materials, structures, andinstrumentation and controls. An ad-vanced set of computational tools are

Basic Discipline Technologies

. Internal fluid mechanics Materials

tr OAp

Structures Instrumentation and controls

being developed and validated with mea-

surement systems that do not intrude onthe results of the test (Ref 1). NASAis advancing the state-of-art in each ofthese disciplines, with an emphasis onmaterials and computational tools.

Materials research for lightweight, high

strength capabilities is focused onpolymeric, intermetallic and ceramic

matrix composites. NASA is advancing

computational capability in fluids and

structures with improved methods that

reduce the time required for complexcalculations, innovative ways to rapidly

describe the shape of new configur-ations, and advanced modeling to improve

the physical accuracy of the analysis.

Research has been initiated to bring the

computational capability of individual

disciplines together into a multidisci-plinary capability that will simultan-

eously simulate the flows, structuresand controls.

Internal Fluid Mechanics

A major effort in internal computational

fluid mechanics is simulating the flowin high speed fans and compressors. Anexample (ref 2) of such a numericalexperiment is presented in the adjacent

ble for the sharp increase in endwallblockage as stall is approached. Thelower right portion of the figure is acontour plot of the axial velocity nor-malized with respect to the tip wheelspeed on an axisymmetric surface ofrevolution at 99 percent of span. Thedashed contour corresponds to zero axialvelocity. The contours within the zerocontour are negative while those withoutare positive. Notice that the region ofnegative velocity extends across theentire passage. As the flow is furtherreduced towards stall, the negativevelocity area would extend forward ofthe rotor inlet plane, indicating thespilling of low energy flow into thisregion. This numerical experiment de-monstrated how the clearance over theforward portion of the fan blade con-trols the flow processes leading tostall.

To validate codes similar to the oneused in the above numerical experiment,NASA has developed the Integrated CFDand Experiment (ICE) Program illustratedin the adjacent figure. The objective

Integrated CFD and Experiment (ICE)

NippalComprehensive knowledge base

Artificial intelligence CFD Inter ctive graphicsr VALIDATION I

Real-time data processing EXPERIMENT Parallel processingSUPPORT

Distributedcomputing'

fi

Experiment CFD

is to tightly couple the experimentaland computational research efforts.This will be accomplished by utilizingparallel processors to reduce the costof CFD calculations, and combine theircapability with graphics to rapidly

reduce and display measurements fromadvanced instrumentation systems in realtime during the experiment. The ICEalso involves storing CFD results andexperimental data as independent databases on a common mass storage system,then retrieving both CFD and experimen-tal results and displaying them througha common graphics interface for furtheroff-line comparison and analysis.

A recent NASA program demonstrating theeffort to validate codes is the LowSpeed Centrifugal Compressor ResearchProgram. It couples the analysis ofcentrifugal compressor flow fields using3D Navier-Stokes codes with experimentalmeasurements acquired in the uniquelarge-size, low-speed centrifugal com-pressor impeller shown in the adjacent

Low Speed Centrifugal Compressor Research

3D Navler-Stokes code predictions 5-ft-diam impellerof fluid particle paths

figure. The results of a numericalprediction of the impeller flow field isshown on the left of the figure. Fluidparticles in the blade boundary layerare being tagged from hub to tip nearthe blade leading edge on both the bladepressure and suction surfaces and thenfollowed as they proceed toward theimpeller exit. The numerical resultindicates that this fluid is being driv-en to the tip of the blade, then passesthrough the tip clearance gap, and accu-mulates in a vortex-like structure whichexits the impeller near the pressure-surface side of the blade passage. Suchresults improve our understanding of thecomplex impeller flow physics and serveas a guide in planning the location andextent of detailed laser anemometer flow

3

field surveys.

Combustors with their complex multiplephase flows, turbulence, and chemical

reactions, are a target for future anal-

ysis. The CFD research emphasizes thedevelopment of efficient and accurate

algorithms and codes, as well as valida-

tion of methods and modelling (turbu-lence and kinetics) for reacting flows.The following figure compares experimentwith numerical prediction of axial drop-

let velocity for a non-reacting spray.

The experiment consisted of an air as-

Mean Axial Droplet Velocity (25 µm) for Nonreacting Spray

0

Radial—115

distance, mm Radial0 115 —115

Droplet

distance, mm0 115

velocity,10 m/sec

Distance `-40 to 100—'of spray 20downstream —16 to 20 ^—from

nozzle, 30 X10 to 12_cm

ao "_0 to 1"``F

co-, N ^, 50Experiment Prediction

listed atomizer spraying vertically

downward into a stagnant environment.Velocity measurements were made with atwo-component Phase/Doppler particleanalyzer and were obtained across the

entire spray. The computer model uti-lized for the predictions is parabolic

with Lagrangian particle tracking, in-

cludes source terms for momentum ex-change between droplets and the gasphase, and considers turbulent disper-

sion of the droplets. Agreement isconsidered to be reasonable.

Heat transfer is another area where CFD

is just beginning to produce practical

results. Turbine cooling passage heat

transfer is critical to turbine life

prediction, and is illustrated in thefigure below. The one-dimensional anal-

ysis includes the many physical and geo-metric turbine passage features listed

on the figure. It was applied to therotating serpentine passage illustrated

to the right of the plot, and provided

Turbine Coolant Passage Heat Transfer Analyses

Leading surface Trailing surface5 — — Comp (smooth)

q Esp(smoom) ° °

1631 4 — comp (turn) ° p;..3 ° Exp (curb) ° q

1568 , Nu/Nust5061 2

ae = zsopo q

1443

13801318 1

0-.4 -.z 0 .2 a

1255 I ,' Rossby number, Ro1192 „y Comparison with rotating serpentine passage1130 _ experimental data10671005 Analysis features

942 Rotational effects

879Entrance and turning effects

817Leading edge impingement

• Ribbed turbulators754 Pin fins (including lateral691 ejection)

Flow branchingThermal analysis of cooled radial turbine Finned passages ca9r- m

excellent agreement with the measureddata for both smooth and rough cooling

surfaces. The analysis was also used to

predict the temperature distribution ofa cooled radial turbine, which is shown

in the figure. Results from the cooledturbine testing will be used to furthervalidate the analysis.

Materials

In its Aeropropulsion Materials Program,NASA is synthesizing new compositions,optimizing the processes for materialformation, and developing basic material

characteristics and property data. This

work is focused on polymeric, interme-tallic and ceramic matrix composites.

This is illustrated in the figure below

PMR Family of PMC's for 500 to 700 + IF

The concept Latentreactive

Qencaps

O'8

350 to 400 'F 550 to 600 T

^O Condensation Addition U.S. Patent'>080 polymerization reaction 3,745,149

0 (no voids)Monomer Encapped Cross-linkedreactants prepolymer network

FIGH7ERS

--^

- Approxi-mateuse

+ N2 postcure

800® (patent applied for)

700

600620

600650

550400

¢y -

temper-ature,

F200

0PMR-15 PMR-II PMR-

V-Cap

Prepregs available commercially gyp.,, a„

Composite Structures Simulation RelatesLocal Effects to Global Response

Laminated composite

IMMMM)M1011.

by a two-step polymerization of monomeris reactants (PMR) process which was

developed by Lewis researchers. This

process allowed liquid and gas reaction

products to escape the composite struc-ture prior to final cross-linking.

Through collaboration with the U. S.Navy and General Electric Company, PMR-

15 engine ducts are flying in the F-404

engines that power the Navy's F-18 Hor-

net fighters. These ducts save about 30

percent of the total weight and cost

over the previous titanium duct. Re-cently, Lewis scientists have increasedpolymer molecular weight, added more

thermally stable end-caps, and by anitrogen post cure, substantially raised

the glass transition temperature toprovide higher ultimate use tempera-tures.

Numerous advanced composite fabrication

processes have been also developed by

NASA scientists. As seen in the adja-

gram includes probabilistic analysis anddesign, nonlinear material properties,

symbolic logic, composite micromechan-

ics, aeroelasticity, fatigue and frac-ture of composite structures, life pre-

diction and aspects of nondestructiveevaluation. These programs, which forthe most part are analytically based,

are experimentally verified and are used

to develop computer codes necessary for

the design of complex engine structures.

Mechanical performance and structural

integrity of high-temperature metal

matrix and ceramic materials is governedby local behavior at the level of the

composite constituents, i.e., fiber andmatrix. Hence, in the analysis anddesign of aircraft engine componentswhich are ultimately to be fabricatedfrom these composite materials, it is

necessary to understand and model the

local behavior of the material over the

component volume and relate its effects

to global structural performance as

shown in the adjacent figure. The crit-Composite Fabrication

Arc spray No commercial applications yetSiC/Ti a Al+Nb composites fabricated

from arc-sprayed monotape

Unetched

Powder cloth SiCiRBSN

+Binder Unidirectional compositeU.S. Patent4,689,188

• . .

RBake — Press

Unit cell model Nonlinearconstituentproperties

P

n,T,l

cent figure, the NASA arc spray method

and the "powder cloth" approach havebeen used to make intermetallic and

ceramic monotapes. Such tapes can thenbe angle plied, laid up, and hot pressedor HIPed to the final desired densityand near-net shape.

Structures

The NASA Aeropropulsion Structures Pro-

ical local behavior is governed by such

factors as imperfect bonding at thefiber-matrix interface, the progressive

nature of microcracking, and nonlinear

dependencies of constituent propertiesover the range of conditions in which

the engine operates. We integrate con-stituent material models, cumulative

damage models, composite mechanics, and

global finite-element structural analy-

sis to analyze this problem. With this

capability, local effects on overall

component behavior can be resolved and

yet adequate efficiency achieved to bepractical for realistic engine component

applications.

Using probabilistic methodology, the

component design survivability can be

mapped by incorporating finite-element

analysis and probabilistic material

properties. As shown in the adjacent

Life Prediction Methods Bridge Gap BetweenSpecimen Testing and Full-Scale Engine Structure

Data analysisSpecimen testing Probability of survival, percent

Io

so WeibullStructure lifeI go distribution

Probability of failure, percent00

6 10 1 ] 20 [ 1000 soLite, stress cycle60

Computing ao

r? Stress analysis 20I.s 7 F, all 12 13 is 15 16,1000

Time

Ii

Probabilityof Failure co-, .a e2

figure, the method evaluates design

parameters through direct comparisons of

component survivability expressed in

terms of Weibull parameters. The method

allows the use of statistical data ob-

tained from laboratory coupon testing

under environmental conditions to be

integrated into life and risk analysis

of full-scale engine structures. It is

possible through an interactive designprocess to minimize the risk of failure

for a given operating time or, converse-

ly, to design for a finite life for a

defined risk. When Weibull parameters

and the stress-life exponent of the

material are unknown, it is permissible

to assume these values in order to ob-tain a qualitative, if not quantitative,

evaluation of a structural design. We

are currently applying these methods tofull-scale structures such as turbineblades and disks where full-scale compo-

nent data exist.

Instrumentation and Controls

The NASA Aeropropulsion Research has along history of investigation in advanc-

ed research instrumentation and propul-

sion controls. Research instrumentationis focused on minimally intrusive con-

tact sensors and nonintrusive optical

measurement systems compatible with the

increasingly hostile environment of

modern engines. A prototype nonintrus-ive optical flow diagnostic system based

on planar laser-induced fluorescence hasrecently been developed for NASP propul-

sion research. Measurements of the

exhaust of two versions of a scramjet

combustor are shown in the figure below.

These represent the OH concentration

Planar Laser-Induced Fluorescence Measurements ofOH Concentration in a Scramiet Combustor

Laser f Laser

Flow Flow

Short Long

for a short combustor configuration

(left) and for a longer one (right).

The more uniform mixing achieved with

the longer combustor is evident in this

picture. Similar maps have beenachieved for other species concentra-

tions as well as for temperature distri-bution. Quantitative as well as quali-

tative data will be obtained from this

system.

Another remote optical measurement sys-

tem is the use of speckle interferometry

for strain measurement. It is aimed atthose situations where the temperature

is beyond the capability of strain gage

alloys and/or where the surface strainis large enough to enter the plastic

region. The technique depends on the

fact that the speckle pattern produced

6

L

by impingement of laser light on a sur-face is caused by slight irregularities

in the surface. This speckle patternthus moves when the surface is strained.

Electronic photographs of this pattern

are taken before and after straining,and are then processed to track the

speckles; thereby measuring the strain.

The left illustration in the figure

Speckle Interferometry for RemoteStrain Measurements

Mirror

Polarized Photo-beam dlode

splitter SpecimenPockets cell

yy\ Acousto-Qi° optic

modulator Mirror

Laser speckle strain Speckle patternmeasurement system

shows the system schematically. Thespeckle pattern (example on right) is

photographed before and after strain

from two different directions. Process-ing of all four images allows the strain

to be separated from any rigid body

motion which might have occurred alongwith the strain.

Because optical fibers are dielectric,

problems with the effects of electromag-

netic interference, electromagneticpulse, and lightning are eliminated.

Also, it is expected that replacing con-

trol-system electrical wiring with opti-

cal fibers will result in weight andvolume savings, as well. The high band-

width capability is advantageous for buslines and offers the potential for all

avionics data to be transmitted over a

single line. To develop and demonstrate

fly-by-light control-system technology,

NASA has undertaken the Fiber-Optic

Control System Integration (FOCSI) pro-

gram. Phase I, initiated in 1985 and

completed in 1986, was a NASA-DOD effort

aimed at the design of a fiber-opticpropulsion/flight control system. Phase

II, a NASA-Navy effort currently in

progress, will provide the system de-

sign, subcomponent and system develop-

ment, and system ground tests. PhaseIII, flight demonstration, has also been

initiated and will culminate in fullFOCSI system flight tests. The FOCSI

propulsion system configuration is shown

FOCSI Propulsion System ConfigurationPropulsion System Prime—General Electric Aircraft Engines

Electro-optics chassisassembly

Fan variable geometry 71Turbine exhaust

/ r gas temperature

Fen speeder i If 1/ / I

rLight off detectorInlet temperature —r i // I r

- r %

r /

^J,

t ^\

Core speed \' \ \ Variable exhaust nozzle\

Compressor inlet temperature s \^-Compressor variable geometry

in the adjacent figure. The full com-

pliment of FOCSI propulsion system sen-sors and the electro-optics chassis

assembly are shown as they will bemounted on the engine.

Current in-house and sponsored research

efforts illustrated in the adjacent

figure vary from the development of

Fiber—Optic Sensors Research

140. ea

Thin film temperature sensor WDM position encoder

r4 ^ 1\

Intensity sensor referencing 1900 °C blackbody temperature sensortechniques

near-term flight prototype control sen-sor systems through far-term investiga-

tion of innovative sensor/sensor-systemconcepts and includes work in;

-Flight prototype aircraft controlsensor systems-On-engine demonstrations of sensorsystems-Laboratory demonstration/testing ofnew sensor concepts-Improved sensor referencing/signalprocessing techniques-Integrated optics/microfabricationtechniques-Electro-optic component research

The overall goal is to develop minia-ture, rugged, passive, optical sensorsystems which operate reliably in theaerospace environment. Shown in thefigure are (clockwise from top left) anovel thin film temperature sensor, awavelength division multiplexed opticalencoder, a blackbody temperature sensor,and laboratory work to improve opticalintensity, sensor accuracy, and preci-sion.

Multidisciplinary Research

Implementing a new technology in aero-space propulsion systems is becomingprohibitively expensive. One of themajor contributors to the high cost isthe need to perform many large-scalesystem tests. Extensive testing is usedto capture the complex interactionsamong the multiple disciplines and themultiple components inherent in complexsystems. The object of NASA work on aNumerical Propulsion System Simulation(NPSS) Program is to provide insightinto these complex interactions throughcomputational simulations. The tremen-dous progress taking place in computa-tional engineering and rapid increase incomputing power expected through paral-lel processing make this concept feasi-ble within the near future. However, itis critical that the framework for suchsimulations be put in place now to serveas a focal point for the continued de-velopments in computational engineeringand computing hardware and software.The NPSS concept will provide thatframework.

Implementation of NPSS requires a hier-archy of codes and models to be in placeto provide a wide range of capabilitiesfrom detailed three-dimensional, tran-sient analyses of components to time-and space-filtered analyses of the sub-systems and systems. Modeling approach-es will be developed for communicatinginformation from a detailed analysis toa filtered analysis. Additional re-search will be required to understandthe mechanisms by which phenomena ondifferent length and time scales commu-nicate. Research is already underway incomputational fluid dynamics and struc-tural mechanics to develop this modelingapproach and will be extended to consid-er processes and scales appropriate forthe entire propulsion system. Illus-trated on the left of the adjacent fig-

Single-Discipline Modeling

ure is the Adamczyk (ref 2) average-pas-sage formulation which will be the fluiddynamic simulation model that will serveas the basis for the integrated systemmodel. The average passage model, whichhas been developed for multistage turbo-machinery analysis, is based on thefiltered forms of the Navier-Stokes andenergy equations. This model was de-signed to resolve only the temporal andspatial scales that have a direct effecton the relevant physical processes. Thestructures modeling, illustrated on theright, will be aimed at developing acomparable computational capability thatwill provide a means to traverse multi-

8

ple scales of spatial resolution with aminimum number of variables at each

level. In this way an analysis canproceed from a blade to a rotor to an

engine core to the complete engine. The

resulting system will have a minimum

number of degrees of freedom consistent

within the objectives of the analysisand will minimize the computational

requirements.

Vehicle Focused Research

To assure the practical application of

the technology developed under the re-search on basic disciplines, NASA focus-

es much of its research on vehicle fo-

cused applications. These applicationsinclude subsonic and supersonic trans-port aircraft, high performance military

aircraft, and hypersonic/transatmospher-

ic vehicles. Examples of this research

follow for subsonic and supersonic

transport aircraft.

Subsonic Transport Research

Propulsion technology for subsonictransports is focused in two main areas:

(1) low-noise ultra-high-bypass (UHB)

Subsonic Transport Propulsion Research

Focused Technologies:.+Ultra-high-bypass ratio cycles

— Ducted props/fans— Low noise

High-efficiency core

ratio cycles and (2) high-efficiencycores. Previous work demonstrated the

technology for fuel-efficient, unducted,

advanced turboprops and that effort is

concluding. Unducted ultra-high-bypass

ratio engines are subject to total

thrust limits due to diameter con-

straints for under-the-wing installa-tions. Thus, current work emphasizes

ducted prop/fan configurations suitablefor large wide-body aircraft powered by

two large-thrust engines mounted under

the wing as shown in the figure above.

The need for larger thrust engines fortwin-engine, long-range aircraft isconstrained by engine diameter. Fur-

ther, to reduce the fan noise level, the

most effective techniques are to reduce

fan tip speed and introduce blade sweep

developed in the Advanced Turboprop

Program. Designers are therefore pre-sented the task of reducing fan tip

speed while increasing fan pressureratio. Shown in the adjacent figure is

New CyclesPylon/wing intersect at2% of wing chord

Size Max. \Constraints diem, Channel— — height,160 in. 14 in. min.

Ground clearance, 23 in. min.—<Ground line

1600r Diameter/Design constrained

corrected Uncon- / Current technology

V tip• 1200 strainedft/sec rDiameter constrained

I lower noise_ Advanced technology

800 —1.28 1.32 1.36 1.40 1.44

Design fan pressure ratio

a result from a cycle study to identify

future technology requirements. The

desired changes in fan tip speed and

pressure ratio are significant challeng-

es and will require advanced technologyto operate at these highly loaded condi-

tions with acceptable levels of fan

surge margin. To fully understand theperformance and noise of such a configu-

ration will require an integrated three

dimensional analysis of the interactionof the fan, stator, and nacelle.

High-efficiency core investigations

center around increasing thermal effi-

ciency by pushing core pressure ratios

9

and temperatures higher. The overallgoal is to maximize engine efficiency

subject to the environmental constraints

of aircraft noise rules and emission

limits. As seen in the adjacent figure,large gains in turbine engine overall

Civil Engine Efficiency TrendsOverall Efficiency

9.3 .4 .5 .61 ,

Ultra-high bypass/.7 High-efficiency core goal

.2

Core 6

/O'LLL

,:C>c AdvancedThermal turbopropEfficiency .5\ Next generation

turbofan

.4R High-BPRTurbolets turbofan turbofan

.3Whittle en ins

.2.3 .4 .5 .6 .7 b

Propulsive Efficiency

efficiency have been made since thefirst turbojets were introduced. Recent

advances such as high-bypass turbofans

and the advanced turboprop have resulted

largely in improvements in propulsive

efficiency. The goal of the current set

of NASA/Industry studies was to empha-

size the core in order to investigatethe potential of improving the thermal

efficiency over that of the next genera-

tion turbofan. A shift in the efficien-cy trend is shown by the arrow curving

to a more vertical direction in the fig-

ure.

A typical 100:1 overall pressure ratio

engine that resulted from the studies,shown in the figure below, consists ofa two-spool geared configuration with a

bypass ratio of 20 to 25. The resulting

fan pressure ratios are 1.3 to 1.4. Low

drag nacelles are required to minimize

the losses associated the high bypassratios. Efficiency improvements areneeded in both the compressor and theturbine to enable thermal efficiency

improvements at the high pressure ratio.

Advanced materials such as ceramic ma-

trix composites (CMC) and intermetallic

matrix composites (IMC) are used exten-

In-Line Engine Configuration

Low noise `Acoustically treatedadvanced fan \ low drag nacelle\FPR 1.3 - 1.4

^_ T High-efficiencycompressor2 - spool

i OPR 100

Advanced / ligearbox i Low NO x/ V-Uncooled50 000 hp CMC / high-efficiency

combustor J turbine(CMC or IMC)

CD-81-54185

sively throughout the hot section of theengine to reduce or eliminate cooling

flow requirements. Since the low-noisefan must be geared to the high-efficien-

cy turbine, advanced gearbox technologywill be needed to achieve the requiredtransmission power of about 50,000

horsepower. As a result of the highoverall pressure ratio, the combustor

entrance pressure and temperature are

very high. This would result in NOXformations exceeding current levels with

current technology combustors. There-fore, low NOX combustor technology mustbe developed for the very small combus-

tors in this type of engine.

High Speed Research Program

The NASA Phase I High-Speed ResearchProgram (HSRP), illustrated in the fig-

ure below, emphasizes solutions to thecritical environmental barrier issues

associated with any future HSCT air-

craft. Two of these barrier issues -

atmospheric ozone depletion and communi-ty noise are primarily propulsion is-

sues. The critical economical viabilityissues will be the emphasis of the pro-posed future effort.

To meet the requirement to minimizeatmospheric ozone depletion will require

10

High-Speed Research Program

Environmental (Phase I)- Ozone depletion

-= - Airport noiseEconomic (Phase ll) - Sonic boom- Range & payload capability- Operating cost- Manufacturing cost'.WMAff

the NOX emissions challenge illustratedin the adjacent figure. Initial two-

HSR NOX Emissions Challenge50

40

dimensional atmospheric impact studiessuggest that ultra low NOX combustortechnology will be required if no ad-verse impact on the ozone layer is tooccur. The standard term for expressingNOX emissions levels is emissions index(EI), defined as the ratio of the gramsof equivalent NO2 produced to the kilo-grams of fuel burned. The figure pres-ents the emissions parameter as a func-tion of a severity parameter which in-creases with increased combustor pres-sure and temperature levels. The ultra-low NOX levels represented by the HSRgoal would have EI's in the range of 3to 8. The top of the open band repre-sents current combustor performance, andthe lower bound of the band represents

performance levels demonstrated in theNASA/Industry Experimental Clean Comb-ustor Program. Obviously, new approach-es to reducing combustor emissions arerequired.

The major elements of the low emissionscombustor technology portion of the HSRPare shown in the figure below. Initial-

Low- Emissions Combustor TechnologyElements

Analysis & Prediction Codes Combustion Experiments2 -1) & 3-1) Chemlcal Fu.l —p-1—d- ~ •- '

Aero kinetics & luel-Wr rrJAng

Cor t Fla tub. with die'Flameproducts

sodt adv. diagnostics

predetlon

Fuel Heat HO. 1Iniectlon transfr d.strmflon

additives ,pi. CH. -00 2. H 2O ♦ H;

Low- Emissions CombustorAdv. Combustor Configurations Rig Demonstrations

Lean Pr.-mlx.Npr.-vaporiz.d 60

Ho. 40Index,

FJ 20 Lsan Rlch

Rich.burrVqul ck-"mMean-bwna

Fuel-Wr equivalence ratio

ly, emphasis will be on the developmentand validation of the computer analysesto predict the details of the combustionprocess within candidate combustor con-figurations. Also, laboratory experi-ments will be conducted to evaluatecandidate combustor configurations andcandidate low-NOX combustion approaches.These laboratory tests will be used inconjunction with advanced diagnostics todevelop a comprehensive combustion codevalidation data base. These experimen-tal data bases and the analytical pre-diction codes will form the basis forconceptual design of candidate low-noxcombustors. The deliverable of thiselement of HSRP will be the demonstra-tion of ultra-low-NOX combustor configu-rations in rig demonstrations. Current-ly, two combustor concepts appear tohold promise for meeting the HSRP emis-sions goal: the lean-premixed-prevapor-ized (LPP) and the rich-burn/quick-quench/lean-burn RQL.

The HSCT noise challenge is illustrated

11

CFDprediction

Exittraversedata

in the adjacent figure. The jet exhaust

HSCT Source Noise Challenge

noise levels at takeoff and landingconditions must be reduced by 15 to 20DB relative to reference conic nozzlelevels before any future HSCT can hopeto meet FAA noise regulation limits. Atthe same time, the nozzle aerodynamicperformance levels must be kept high ifvehicle overall mission performancegoals are to be met. This combinedacoustic-aerodynamic challenge is oftenexpressed as a ratio of decibel noisereduction to resultant percent thrustloss. For a viable HSCT design thisratio should be in the neighborhood of4:1. As this figure shows, currenttechnology would yield a nozzle designwith a ratio of no better than 2:1.

CFD/Translating Probe Comparison and Mixing

Exittraverse

Good mixing

CFD Exit traverse:Excellent agreement

In attempting to meet the FAA noiselimits with a HSCT nozzle, CFD codes arebeing used to analyze the internal mix-ing of ejector nozzles. The figureabove presents a comparison of the tem-perature profiles from a two-dimensionalmodel test and a Navier-Stokes calcula-tion. The agreement is judged to beexcellent, and the results suggest thatthe CFD computer codes will have a crit-ical role in designing the complex flowfield of an HSCT low noise ejector noz-zle.

Concluding Remarks

The potential for increased efficiency,higher speeds, and improved environmen-tal compatibility combine to challengethe aeropropulsion manufacturers of thefuture. NASA is working on developingthe tools in the critical disciplineareas of internal fluid mechanics, in-strumentation and controls, materials,and structures to allow the design offuture propulsion systems that meetthose challenges. In areas where thefuture performance goals are in sight,it is demonstrating the application ofthose tools to future advanced propul-sion systems to make the marketing ofsuch a system an attractive opportunity.

References

1. Staff, Lewis Research Center:Aeropropulsion '91. NASA CP 10063,March 1991.

2. Adamczyk, J. J.; Celestina, M. L.;Greitzer, E. M.: The Role of TipClearance in High-Speed Fan Stall.ASME Paper 91-GT-83, June 1991.

12

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1992 Technical Memorandum4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

The Future Challenge for Aeropropulsion

WU-505-626. AUTHOR(S)

Robert Rosen and David N. Bowditch

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATIONREPORT NUMBER

National Aeronautics and Space AdministrationLewis Research Center E-6943Cleveland, Ohio 44135 - 3191

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National Aeronautics and Space AdministrationWashington, D.C. 20546-0001 NASA TM- 105613

11. SUPPLEMENTARY NOTES

Prepared for Acroengine 92, Moscow, Russia, April 6-12, 1992. Robert Rosen, National Aeronautics and SpaceAdministration, Washington, DC 20546; David N. Bowditch, NASA Lewis Research Center. Responsible personDavid N. Bowditch, (216) 433-5729.

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13. ABSTRACT (Maximum 200 words)

NASA's research in aeropropulsion is focused on improving the efficiency, capability, and environmental compatibility for allclasses of future aircraft. The development of innovative concepts, physical understanding and theoretical, experimental andcomputational tools provide the knowledge base for continued propulsion system advances. Key fundamental enabling technolo-gies include advances in internal fluid mechanics, structures, light-weight high-strength composite materials, and advanced sensorsand controls. Recent emphasis has been on the development of advanced computational tools in internal fluid mechanics, structuralmechanics, reacting flows, and computational chemistry. The improved computational capability and advanced materials are beingused to develop advanced propulsion system component technology, for example, lightweight turbomachinery with improvedefficiency, combustor systems that retain high combustion efficiency while reducing harmful emissions, and low noise, lightweightexhaust systems. The fundamental knowledge base and component technology form the physical and analytical foundation forfocused research activities. For subsonic transport applications, very high bypass ratio turbofans with increased engine pressureratio are being investigated to increase fuel efficiency and reduce airport noise levels. In a joint supersonic cruise propulsionprogram with industry, the critical environmental concerns of emissions and community noise are being addressed. NASA is alsoproviding key technologies for the National Aerospaceplane, and is studying propulsion systems that provide the capability foraircraft to accelerate to and cruise in the Mach 4-6 speed range. The combination of fundamental, component and focusedtechnology development underway at NASA will make possible dramatic advances in aeropropulsion efficiency and environmentalcompatibility for future aeronautical vehicles.

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Aeropropulsion; Turbine engine 1416. PRICE CODE

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