MIT’s N+3 Project:

The D8 Aircraft Concept

and Its Boundary Layer Ingestion Benefit

Technology Lead: Alejandra Uranga auranga@mit.eduPrincipal Investigator: Edward Greitzer greitzer@mit.eduChief Engineer: Mark Drela drela@mit.edu

MIT / Aurora / Pratt & Whitney

4th International Workshop on Aviation and Climate ChangeUniversity of Toronto Institute for Aerospace Studies

May 28, 2014

Summary

I Closer integration of propulsion system and airframe provides newopportunities to reduce fuel burn and emissions of commercial aircraft

I Boundary layer ingestion (BLI)

I Novel configurations

I System optimization (airframe, engine, operations)

I Flow power and dissipation in power balance framework provide usefulmetrics for integrated configurations

MIT N+3 Phase 2 1 / 32

True OptimumOptimization of the aircraft as an integrated system can reach higher levels offuel e�ciency than separate optimization of airframe and propulsion system

. existing engines

existing airplanes

W/S , . . .

t 4

Λ ,

FPR,BPR,T

EngineParameters

AirframeParameters

true optimum

fuel burnisocontours

h cruise t/cM ,

OperatingParameters

.

.

. . .

airframer design domain

engine manufacturer design domain

apparent (false) optimum

MIT N+3 Phase 2 2 / 32

M. Drela

MIT N+3 Project

NASA N+3 Program, Fixed Wing Project

I Develop advanced aircraft concepts and enabling technologiesfor step improvements in fuel e�ciency and emissionsof commercial aircraft entering service in 2025 – 2035

Phase 1 (2008 – 2010)

I MIT-led team developed the double-bubble D8 aircraft concept

I Opportunity to impact the way the industry thinks about aircraft andpropulsion

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The D8 Aircraft ConceptMIT N+3 D8.2

MIT N+3 Phase 2 4 / 32

I B737-800/A320 class

I 180 PAX, 3,000 nm range

I Double-bubble lifting fuselagewith pi-tail

I Two aft, flush-mounted enginesingest ⇠ 40% of fuselage BL

I Cruise Mach 0.72

�37% fuel with current tech(configuration)

�66% fuel with advanced tech(2025-2035)

No “magic bullet”

E. Greitzer et al. 2010, NASA CR 2010-216794

MIT N+3 Phase 2 5 / 32Photos NASA/George Homich

System Impact of BLI

BLI benefitsI

Aerodynamic (direct) benefitsI Reduced jet and wake dissipationI Reduced nacelle wetted area

ISystem-level (secondary) benefits

I Reduced engine weightI Reduced nacelle weightI Reduced vertical tail sizeI Compounding from reduced overall weight

“Morphing” sequence: B737-800 7! D8I Features of D8 introduced one at a time

I Sequence of conceptual designs, optimized at each step (TASOPT)

MIT N+3 Phase 2 6 / 32

E. Greitzer et al. 2010, NASA CR 2010-216794

M. Drela 2011, AIAA 2011-3970

Morphing Sequence: B737-800 7! D8.2 7! D8.6

0

0.2

0.4

0.6

0.8

1

88 %

81 %

82 %

67 %

66 %

100 %

op

tim

ize

d7

37

-8

00

M=

0.8

,C

FM

56

en

gin

e

0

slow

to

M=

0.7

2

1

D8

fu

se

la

ge,

pita

il

2

re

ar

po

dd

ed

en

gin

es

3

in

te

gra

te

de

ng

in

es,

BL

I

4

op

tim

ize

en

gin

eB

PR

,F

PR

5

20

10

en

gin

es

8

Fuel

Burn

63 %

D8.2

6 7 9 10

20

35

en

gin

es

20

35

ma

te

ria

ls

win

gb

ot.

NL

F

sm

art

stru

ct

48 %

38 %

35 %

34 %

D8.6

- 15 %

MIT N+3 Phase 2 7 / 32

Phase 2: Nov. 2010 – Nov. 2014

Research thrusts

I Airframe-propulsion system integration (Task 1)

I Define/design aft section of D8 (integration of engines into fuselage)

I Quantify aerodynamic benefit of BLI

I Propulsor performance with distortion from BLI

I Phenomena, expected (and unexpected) behavior

I High e�ciency, high pressure ratio small core engines (Task 2)

I Limits to performance

I Technology opportunities for performance enhancement

I Innovative propulsion system architectures

MIT N+3 Phase 2 8 / 32

NASA N+3 Phase 2

How

I Direct, back-to-back comparisonof non-BLI and BLI configurations(podded) (integrated)

I Turbomachinery characterization

Tools

I Experiments at NASA Langley14⇥22 wind tunneland MIT tunnels

I Computational studies

I Close collaboration with NASA

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Outline

1 Introduction

2 MethodologyPerformance Metric for BLIConfigurationsApproach

3 Results

4 Summary

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Nomenclature

FX , CX =FX

q1SNet stream-wise force (“drag minus thrust”)

PE , CPE =PE

q1SV1Electrical power supplied to propulsors

PK , CPK =PK

q1SV1Mechanical flow power through propulsors

V1 , q1 =1

2⇢1V 21 Free-stream (tunnel) speed, dynamic pressure

S Reference area (1686 in2, 1.088 m2 at 1:11 scale)

D Propulsor fan diameter (5.67 in, 0.072m at 1:11 scale)

MIT N+3 Phase 2 11 / 32

BLI Analysis

I Ambiguous decomposition into drag and thrust(airframe) (propulsion system)

I Use power balance method instead of force accounting

I BLI reduces wasted KE in combined jet+wake (mixing losses)

wake, or “draft”

WastedKinetic Energy

Zero NetMomentum

combined wake and jet

propulsor jet

+

+

+

+

+

+

+

-

-

-

MIT N+3 Phase 2 12 / 32

M. Drela 2009, AIAA Journal 47(7)

Power Balance method

Consider mechanical energy sources and sinks: [ Power In ] = [ Dissipation ]

⇢⇢PS|{z}shaftpower

+ ⇢⇢PV|{z}p dVpower

+ PK|{z}mechanicalflow power

= �jet

+ �wake

+ �fuse

+ �vortex

+ Ė|{z}power

out of CV

PK

�wake

�wake �vortex

�vortex�fuse

�fuse

PK

�jet

�jet

Non-BLI Configuration

BLI Configuration

MIT N+3 Phase 2 13 / 32

M. Drela 2009, AIAA Journal 47(7)

Power Balance methodAerodynamic (direct) benefit of BLI configuration

Reduced jet + wake dissipation, reduced nacelle wetted area

P

BLI

K � �BLIjet| {z }Net propulsive power

= PBLIK ⌘BLI

p|{z}>⌘p

= �BLIwake| {z }

(1�fBLI)�wake

+ �BLIfuse

+ �vortex

PK

�wake

�wake �vortex

�vortex�fuse

�fuse

PK

�jet

�jet

Non-BLI Configuration

BLI Configuration

MIT N+3 Phase 2 14 / 32

M. Drela 2009, AIAA Journal 47(7)

BLI Benefit

BLI benefit (aerodynamic)

Savings in power required for given net stream-wise force

with BLI engines relative to non-BLI engines

Power metric

Mechanical flow power transmitted to the flow by the propulsors

PK =

I(po � po1)V · n̂ dS

BLI benefit ⌘ PKnon-BLI � PKBLIPK

non-BLI

����at given FX

MIT N+3 Phase 2 15 / 32

Obtaining PK

Method 1: Integration of the flow over cross-section of the stream-tubeupstream and downstream of the propulsor: flow survey data

PK =

Z

exit

(po � po1)V · n̂ dS �Z

inlet

(po � po1)V · n̂ dS

exit

inlet inlet

exit

Method 2: From electrical power provided to the propulsor motor,which is related to mechanical flow power through fan and motor e�ciencies

PK|{z}mechanicalflow power

= ⌘f|{z}fan

e�ciencyPK/PS

⇥ ⌘m|{z}motor

e�ciencyPS/PE

⇥ PE|{z}electricalpower

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Podded (non-BLI) Configuration

MIT N+3 Phase 2 17 / 32

Photo NASA/George Homich

0 50 in10

Integrated (BLI) Configuration

MIT N+3 Phase 2 18 / 32

Photo NASA/George Homich

0 50 in10

Back-to-Back Comparison

MIT N+3 Phase 2 19 / 32

Podded(non-BLI)

Integrated(BLI)

BLI benefit =CPK

podded

� CPKintegrated

CPKpodded

�����at given CX

Bases for ComparisonGiven a BLI propulsor with some jet velocity, mass flow, nozzle area,

how do you choose an “equivalent” non-BLI propulsor as basis for comparison?

1 1.2 1.4 1.6 1.8

1

1.02

1.04

1.06

1.08

1.1

0.98

0.8

CPKCPK , BLI

A

A

BLI propulsor

Non−BLI propulsorswith same net force

same Vjet

same

same fanm

A

same PK

.

smaller propulsor

nozzle

nozzle

nozzle, BLI

lowerpropulsorpower

MIT N+3 Phase 2 20 / 32

(=

Scaling Considerations for Low Speed Study

No dynamic symilarity between full-size D8 and experiments:Reynolds number and Mach number are not matched

) How do we ensure BLI benefit results are representative of full-size conditions?

I Airframe scaled geometrically by 1:11 from full-size, current-technology D8(fuselage, wing and tail planforms, fan diameter)

I Wing profiles and sweep designed for low speed (low Mach, low Re)

I Propulsion system scaling

I Use same propulsion system for both BLI and non-BLII Data taken with varying nozzle area to bracket design power and

propulsive e�ciency at cruise condition

I Investigate o↵-design points

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Experimental Approach

I NASA Langley 14⇥22 Foot Subsonic Wind TunnelV1 = 70 mph, M1 = 0.09, Rec = 570,000

I 1:11 scale, 13.4 ft span, powered D8 model

I Podded and integrated configurations share a large part of hardwareI Common wings and front 80% of fuselageI Common propulsor units plug into interchangeable tails

(fan stage, motor, center-body, housing, nozzle, electronics)I All model surfaces tripped

I Data collectionI Forces and moments (internal NASA balance)I Electrical powerI Fan wheel speedI Rake system for total and static pressure surveys

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Outline

1 Introduction

2 Methodology

3 ResultsBLI BenefitFlow SurveysDissipation

4 Summary

MIT N+3 Phase 2 23 / 32

BLI BenefitCPK BLI < CPK non-BLI for any given CX

or CX BLI > CX non-BLI for any given CPK

0 0.02 0.04 0.06 0.08 0.1

-0.03

-0.02

-0.01

0

0.01

0.02

0.03

C

PKMechanical flow power coe↵.

integrated

podded

6% BLI benefit

at simulated cruise

C

X

Streamwise

force coe↵.

(“drag � thrust”)

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Survey Propulsor Inlet and Outlet

MIT N+3 Phase 2 25 / 32

Rotating rake systemin wind tunnel experiments

Total Pressure

Inlet Rake

Total Pressure

Exit Rake

Integrated Propulsor Ingested Flow

MIT N+3 Phase 2 26 / 32

Experiments Left propulsor Right propulsor BL profile

Total pressure coe�cient Cpt =pt � pt1

q1

z

Dfan

y/Dfan-0.6 -0.4 -0.2 0 0.2 0.4 0.6

0

0.2

0.4

0.6

0.8

1

1.2

-0.75 -0.5 -0.25 0

0

0.2

0.4

0.6

0.8

1

1.2

Left

Right

-1

-0.8

-0.6

-0.4

-0.2

0

-0.6 -0.4 -0.2 0 0.2 0.4 0.6

y/Dfan

z

Dfan

y/Dfan-0.6 -0.4 -0.2 0 0.2 0.4 0.6

0

0.2

0.4

0.6

0.8

1

1.2

-0.75 -0.5 -0.25 0

0

0.2

0.4

0.6

0.8

1

1.2

Left

Right

-1

-0.8

-0.6

-0.4

-0.2

0

-0.6 -0.4 -0.2 0 0.2 0.4 0.6

y/Dfan

↵ = 2�

11 kRPM(cruise)

↵ = 6�

13 kRPM(climb)

“Benign” stratified flow

Integrated Propulsor Exit Flow

MIT N+3 Phase 2 27 / 32

Experiments Left propulsor Right propulsor Jet profile

Total pressure coe�cient Cpt =pt � pt1

q1

0 1 2

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Left

Right

-0.6 -0.4 -0.2 0 0.2 0.4 0.6-0.6 -0.4 -0.2 0 0.2 0.4 0.6

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

z

Dfan

y/Dfan y/Dfan

-0.4

0

0.4

0.8

1.2

1.6

0 1 2

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Left

Right

-0.6 -0.4 -0.2 0 0.2 0.4 0.6

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

z

Dfan

y/Dfan

-0.4

0

0.4

0.8

1.2

1.6

-0.6 -0.4 -0.2 0 0.2 0.4 0.6

y/Dfan

↵ = 2�

11 kRPM(cruise)

↵ = 6�

13.5 kRPM(climb)

Clean exit flow

Dissipation as a Measure of Configuration Performance

Cut X=130

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

Integrated

Podded

Unpowered

⇣

wing

fuselage

nacelle

jet

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Dissipation as a Measure of Configuration Performance

Both podded and integrated configurations show separation at thejunctures of vertical tails and horizontal tail: ⇠ 1.2% of total dissipation

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Dissipation computed

on wake plane down-

stream of separation

Outline

1 Introduction

2 Methodology

3 Results

4 Summary

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Conclusion

I Aero BLI benefit: 6%± ? saving in power (fuel) with BLI at cruise

I Estimated total, system-level fuel burn savings of 15% enabled by BLI

I D8 with estimated 37% fuel saving over conventional tube-and-wingcan be built “today”

Data supports feasibility of using BLI to improve fuel e�ciencyand viability of D8 concept

An exciting project aimed at

changing the way industry thinks about aircraft and propulsion,

and the look of civil transport aircraft

MIT N+3 Phase 2 31 / 32

Acknowledgments

NASA Fundamental Aeronautics Program, Fixed Wing ProjectCooperative Agreement NNX11AB35A

MIT N+3 team

Partners at Aurora Flight Sciences, Pratt & Whitney, NASA

Harold (Guppy) Youngren of Aerocraft Inc.

Sta↵ at NASA Langley 14⇥22 Foot Subsonic Wind Tunnel

NASA Fixed Wing Project management

MIT N+3 Phase 2 32 / 32

1IntroductionMIT N+3 ProjectSystem Impact of BLINASA N+3 Phase 2

2MethodologyPerformance Metric for BLIConfigurationsApproach

3ResultsBLI BenefitFlow SurveysDissipation

4Summary