Overview of Variable-Speed Power-Turbine Research

The vertical take-off and landing (VTOL) and high-speed cruise capability of the NASA Large Civil Tilt-Rotor (LCTR) notional vehicle is envisaged to enable increased throughput in the national airspace. A key challenge of the LCTR is the requirement to vary the main rotor speeds from 100% at take-off to near 50% at cruise as required to minimize mission fuel burn. The variable-speed power-turbine (VSPT), driving a fixed gear-ratio transmission, provides one approach for effecting this wide speed variation. The key aerodynamic and rotordynamic challenges of the VSPT were described in the FAP Conference presentation. The challenges include maintaining high turbine efficiency at high work factor, wide (60 deg.) of incidence variation in all blade rows due to the speed variation, and operation at low Reynolds numbers (with transitional flow). The PT -shaft of the VSPT must be designed for safe operation in the wide speed range required, and therefore poses challenges associated with rotordynamics. The technical challenges drive research activities underway at NASA. An overview of the NASA SRW VSPT research activities was provided. These activities included conceptual and preliminary aero and mechanical (rotordynamics) design of the VSPT for the LCTR application, experimental and computational research supporting the development of incidence tolerant blading, and steps toward component-level testing of a variable-speed power-turbine of relevance to the LCTR application.

National Aeronautics and Space Administration

Fundamental Aeronautics ProgramSubsonic Rotary Wing Project

O i f i bl d t bi h

Dr. Gerard E. WelchTechnical Lead, Propulsion/Engines

Overview of variable-speed power-turbine research

2011 T h i l C f

1www.nasa.gov

2011 Technical ConferenceMarch 15-17, 2011Cleveland, OH

VSPT research team

NASA in-house• ARL-VTD / G. Skoch, D. Thurman• NASA RTT / A. McVetta, S. Chen, Dr. G. Welch• NASA RTM / C. Snyder• NASA RXN / Dr. S. Howard• NASA DER / M. Stevens• ASRC / Dr. P. Giel• U. Toledo / Dr. W. To• Ohio State U. / Dr. A. Ameri

RTAPS contracts on VSPT

2

Overview of VSPT research

• Introduction– Need for variable-speed tilt-rotor

S l ti h i i bl d t bi (VSPT)– Solution approach using variable-speed power turbine (VSPT)

• Key technical challenges / research needs

• Research activities

• Summary

3

Alleviate airport congestion utilizing LCTR

Large Civil Tilt-RotorTOGW 108k lbff

Payload 90 PAXEngines 4 x 7500 SHPRange > 1 000 nmRange > 1,000 nmCruise speed > 300 knCruise altitude 28 – 30 kft

Principal challenge for LCTR is required variability

Acree, C. W., Hyeonsoo, Y., and Sinsay, J. D., “Performance Optimization of the NASA Large

LCTR is required variability in main-rotor speed:– 650 ft/s VTOL

350 ft/ t M 0 5 ip g

Civil Tiltrotor,” Proc. International Powered Lift Conference, London, UK, July 22-24, 2008.

– 350 ft/s at Mn 0.5 cruise

4

Approach to vary main-rotor speed

• Fixed-speed PT w/ multi-gear-ratio transmission– High efficiency design-point operation from take-off to cruise

C l it d i ht f i bl t i i– Complexity and weight of variable transmission– Need to shift gears

• Variable-speed PT w/ fixed gear-ratio transmission

– Wide PT speed range, 54% < N < 100% or

, h 0

/U2

54% < NPT < 100%– Lower efficiency potential– Added weight to turbine/shafting

e w

ork

fact

o

Avoid complexity and weight of variable transmission & the need to shift gears

Stag

e

Flow coefficient, ux/U 5

Impact of variable-speed power turbine on cruise efficiency

6

Martin D′Angelo, GE-LynnNASA CR/1995-198380

~

'#. ~

>-0 Z W 0 Ii: LL W W III :l II: 0 )( c(

2

PROP/ROTOR AND PT DESIGN POINT EFFICIENCY va % Npt MDHC TW Rotor. 3 Stage FIxed Geometry PT. Max CruIse @ M=.7

e2 QO

88

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ETA'PI (~ Sl'~' Fa PT) -86 - -- .. _- .. _-, •. 84

82

80

78 76

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ETA prop (MDHC TW ROIOr) - I'-.. -........

........... 70 ......... 68 ......... 88

64

62 - .........

-........... - _. - ETAprop • ET pl -

""'" 60 ......... sa

so 52 $ 4 56 SI 80 12 ,. 66 4' 70 7 2 7 4 76 18 80

Npl DESIGN (%)

•

Key technical challenges for VSPT

• Aerodynamics– Efficiency at high work factor

I id i ti i d b d h– Incidence variation required by speed change– Operation at low Reynolds number

• Rotordynamics• Rotordynamics– Avoidance / management of shaft modes through speed range

7

Aerodynamics – efficiency at high work factor

• Specific power is approximately 200 SHP/(lbm/s) at 2 kft take-off and 28 kft cruise

• If 50% speed reduction

ConstruhmW )(/ 0

95Improved

Aero40 to 60-deg.negativeIf 50% speed reduction

th

2r3-stage

90η

45E9 AN2

7862rpm

1976 LPTs(O t )At take off

negativeincidence

then

2 u Efficiencies of 1965

Smith Chart

3-stage

AMDCKO

4-stage(D′Angelo)

3 stage(D′Angelo)

85e ef

ficie

ncy,

η (Oates)At take-off(off-design100% speed)

45E9 AN2

8147rpm

and

420

Uh

Smith Chart3-stage

(D′Angelo)

80

Stag

e

Design-point efficiency vs. work factor

U

8

Work factor, ψ1 2 3 4 5

80

Incidence variation & low Reynolds number

Los

s• Required incidence variation with speed– Impact of aerodynamic loading level

(Zweifel)

i-iopt

(Zweifel)– Impact of loading schedule– Use of variable stators/EGVs

p

NPT = 50%NPT = 100%Blade row loss vs. incidence

1

• Low Reynolds number at take-off and cruise (30 to 50k/in.)

– Impact on design-point loss (efficiency 0.1coef

ficie

nt

L1M bladingL1A blading

lapse)– Impact on incidence-range at acceptable

loss levels– Influence of unsteadiness 0 01

Prof

ile lo

ss

LCTRoperationInfluence of unsteadiness

9High-load LPT blade at low-Re

0.0110,000 100,000 1,000,000

Exit Reynolds number, Recx,2

VSPT aero research and technology development needs

• MDO of variable-speed PT at component and engine level Harvey et

al., 2000

• Efficient high-load, high-turn aerodynamics– Secondary flow management using 3-D

blading (lean and bow) and endwall

,

contouring

• Aerodynamics of high negative incidenceCharacterize 2 D and 3 D loss mechanisms

Rotor 1 attake-off– Characterize 2-D and 3-D loss mechanisms

at high (40 to 60 deg.) negative incidence

• Aerodynamics of low-Re number flows– Turbulence sub-models for transitional flow

into RANS/URANS solvers– Multistage experiments and 3-D URANS

simulation capability – unsteadiness

Praisner and Clark, 2007

p y

10

RESEARCH ACTIVITIESRESEARCH ACTIVITIES

11

Research activities

• Conceptual aero-design, optimization, and analysis

• Cascade testing of incidence-tolerant blading

• Computational methods for LPT/PT

• Rotordynamics of LCTR PT rotor

• VSPT component / engine testing

12

Conceptual aero-design of VSPT for LCTR

• In-house effort (AFRL TDAAS system)– Meanline analysis using F. Huber’s meanline tools– Design at cruise with AN2 limit at take-off: 4-stage

First stage LCTR VSPT

Z = 1.1, 120-deg. turning

– Design at cruise with AN limit at take-off: 4-stage– 2-D blade profiles set in AFRL TDAAS– 3-D analysis using SWIFT RANS mixing-plane code

14

p0 deficits

• Williams International study contract– Mission fuel burn sets design speed– Evaluated work and flow coefficients and

blade thickness (nominal & thin): 4-stageHigh design

Low design( ) g

– FOILGEN (blades) & VORTEX (analysis)

• Rolls-Royce (RRC / RR-NAT) study contractcontract

– Tailored to high flow coefficient– Technology curves: 4-stages– Loss buckets biased to +5-deg. incidence at cruise 50%-span section– Optimized blade shapes using AIRFOILOPT

13

50% span section

3-D computational analysis of embedded stage with speed variation

Variable-speed power turbinefor the Large Civil Tilt Rotor

Draft final report

Mark SuchezkyWilliams International Co., LLC

14

3-D computational analysis of rotor of 4-stage VSPTRTAPS VSPT Contract NNC10BA14B

Design Optimization of Incidence-Tolerant Blading Relevant to Large Civil Tilt-Rotor Power Turbine

ApplicationsNASA/CR-2011-217016

A. Ford, M. Bloxham, E. Turner, E. Clemens, S. GeggRRC / RR-NAT

15Loss bucket of embedded rotor 2 of 4-stage VSPT

NASA GRC transonic linear cascade

• Aero and heat transfer testing at wide range of M, Re, Tu, and flow incidence.

NASA Blade 1; 99-GT-125

2.0 maximummass flow

57 lbm/sec

CW-22; Transonic Turbine Blade CascadeOperating Flow Envelope

7.06.0

NASA Blade 1; 99 GT 125G.E. Blade 1; 2000-GT-0209G.E. Blade 2; GT2003-38839EEE Tip Section Blade1.5

isentropicexitMachnumber,

minimumexhaust

pressure

m

5.04.0

3.0isentropic

pressureratio

0.5

1.0Ma2,i2.0

1.51.41.31.21 1

ratio,Pt,1

P2

14.7 psia

E3 des1/21/4E3 Ma2,des = 0.74

isentropic exit unit Reynolds number,

0.00.1 0.2 0.3 0.5 0.7 1.0 2.0 3.0 5.0 7.0 10.0

Re2,i 106 [1/ft]

maximuminlet pressure

= 23.0 psia

1.1

1.0

pwg1/11/2011

P t=14

1/8Ma2 = 0.34

Schematic diagram of NASA transonic linear cascade

Tunnel test conditions

16P. Giel & A. McVetta

NASA transonic linear cascade (cont.)CW-22 Probe Slots with E3 Blades

• Completed mid-span surveys of EEE tip-section• Test cell modification for negative incidence

i t

5

6

passage4

passage5

Sta. 2x=5.561

Sta. 3x=6.811

Sta. 4x=8.062

+13

+13

+13

+13

+13

48.8

(+10)

33.8(5

)

38.8(des)

instr. ps

primary

instr.0

5

bal)

[inc

hes]

EEE blade range requirements

• First-entry VSPT blading inpreparation

4

3

4

passage3

Sta. 0x=5.000

Sta. 1x=0.881

0

2

0

2

0

2

0

2

0

60.8metal

64.4 designflow

48

yg = 8.375

instr. ss

yg = 5.063

9.450

12.672

15.844

58.8 (

+20

)

-15

-10

-5

E3 Tip Section Bladestip gap on blades 4, 5, 6Cx = 5.119 pitch 5 119

y(g

lob

pack and survey planes50%-span

section

RR-NAT blading2

-5 0 5 10

pitch = 5.119 1 = 33.8 (facility minimum)2 = 60.8 (T.E. metal angle)

x [inches]

0 6

0.7

0.8

Re1= 1.0des; PR=desRe1=1/2des; PR=desRe1=1/4des; PR=desRe1=1/4des; PR=0.75desRe1=1/8des; PR=0.75des

Cptot P1 P

P1 P2

Cptot =

0 6

0.7

0.8

Re1= 1.0des; PR=desRe1=1/2des; PR=desRe1=1/4des; PR=desRe1=1/4des; PR=0.75desRe1=1/8des; PR=0.75des

P1 P

P1 P2

Cptot

Cptot =

RR NAT blading

0.3

0.4

0.5

0.6

0.3

0.4

0.5

0.6

y/pitch-2.0 -1.5 -1.0 -0.5 0.0 0.5

0.0

0.1

0.2

y/pitch-2.0 -1.5 -1.0 -0.5 0.0 0.5

0.0

0.1

0.2

Total-pressure coefficient as a function of pitchwise position

a.) -5 degrees incidence b.) +10 degrees incidence

P. Giel & A. McVetta17

Computational methods for LPT/PT

• Turbulence sub-model for transitional flow in LPTs (A. Ameri)

– Evaluated turbulence models for RANS solversEvaluated turbulence models for RANS solvers– Selected 3-eqn model (l, , ) of Walters &

Leylek– Compared to heat transfer data from GE2 LPT

bl d (Gi l B l d B k )blade (Giel, Boyle, and Bunker)

• Multistage URANS simulation capability (W To)

Computed Nusselt number for GE2 LPT blading (CFD A. Ameri; Experiment P. Giel et al.)

(W. To)– Utilize in-house code TURBO (J. P. Chen)– Applied to 1.5 stage LSRR turbine (Dring, UTC)– Openly available geometry and steady & Rotor speed 410 rpm

InletMach ~0 063p y g y yunsteady data sets

• AeroDynamic Solutions, Inc. (ADS) WAND/LEO d

Inlet Mach ~0.063Flow coefficient ~0.73Mass flow ~17.9 kg/s

These 2-D contours are plotted at the interface planeWAND/LEO codes

Contours of instantaneous total-pressure in LSRR multistage turbine rig computed using

TURBO multblock code (W. To).

at the interface plane (local scale)

RotordynamicsPT R

• Rotordynamics model for LCTR w/ 50% speed range (A. Howard)

Model of LCTR2 HP LP and

HP Rotor

LP Rotor

PT Rotor

– Model of LCTR2 HP, LP, and VSPT rotors

– Geometry from WATE code (Doug Thurman)

– Some assumptions on bearing location modeled after T700

DyRoBeS model of LCTR rotors (A. Howard)

• Rotordynamics model of T700-700 createdcreated

– Supporting assessment of component test capability

Critical speed map showing first four critical speeds of PT-shaft in LCTR2 operating range

(A. Howard)

Integrated Aero/Propulsion system (IAPS) FY25

SRW.100Integrated

FY20-25FY11 FY12 FY13 FY14 FY15 FY16 FY17 FY18 FY19

SRW.111I d l i

SRW.107VSPT Component

T t

SRW.109Integrated fixed engine/variable

SRW.102Plan for

SRW.103Plan for HPC follow-on

SRW.108Axi-centrifugal teg ated

Aeromechanics/Propulsion System

(IAPS)

Integrated propulsion system demo, phase 1

SRW.101V i bl d SRW 10

Test engine/variable transmission demo

Propulsion/Aero Demos

SRW.104TTR installation checkout (T18)

activity in CE-18Axi centrifugal

compressor experiment SRW.113Simulation of controls for

variable speed rotor

SRW.112Integrated propulsion SRW.106

SRW.110Variable speed engine Variable speed

engine/gearbox system analysis 2

SRW.105Advanced drive concepts

g p psystem demo, phase 2 with shifting controls

Slowed rotor aeromechanics/dynamics demo

Variable speed engine demo

T700 engine

Inletplenum

2-speedtransmission Flywheel

Torquemeter

WaterbrakeLube package

20Notional layout for integrated engine/transmission demo

(M. Stevens)

VSPT component testing – first steps

• Assessment of in-house VSPT test capability (G. Skoch)

– T700-700 engine in the Engine Component Research Laboratory (ECRL)

• Engine and power absorption capability• Engine controls• Integration of rating / survey instrumentation• PT rotordynamics / shaft mode interactions

– NASA GRC warm turbine test facility (W-6)

• RTAPS study contracts– Williams International

Notional instrumentation layout for VSPT component test in T700 (M. Stevens)

• 4-stage VSPT in W-6• Match first and last stage Re

– Rolls-Royce• Growth AE1107Growth AE1107• 3.5 stage VSPT/EGV in W-6• Match Re at take-off & cruise

• External options being exploredPl d AATD 6 2 t– Planned AATD 6.2 component program

21

Williams Int. VSPT for LCTR(M. Suchezky & Scott Cruzen)

Summary

• Key aerodynamic challenges of VSPT– Attainment of high efficiency (> 0.88) at high work factors (2.5 to 3.5)

Wid i id i ti i i hi h ti i id– Wide incidence variation over mission - high negative incidence– Low unit Reynolds numbers (30 < Re/cx < 50k /in.)

Shared by variable-speed PT and fixed-speed PTsShared by variable speed PT and fixed speed PTs

• Needs: – Low-loss, incident-tolerant vane, blade, and EGV blading, , , g– Ability to manage / avoid engine shaft critical speeds during VSPT speed change

• VSPT research effort at NASA GRC– Develop experimentally validated design methods and computational tools/modeling

for design/optimization of low-loss, incidence tolerant blading– Continue work with industry and DoD partners to refine VSPT design / blading, and

path to component and engine testpath to component and engine test

22

Acknowledgements

• Mr. Robert J. Boyle (former Distinguished Research Associate, NASA GRC) for early assistance in formulation of VSPT research effort

• Dr. Rodrick V. Chima (NASA GRC) for assistance with rvcq3d code

• Dr. John P. Clark (AFRL) for providing the AFRL Turbine Design and Analysis SystemSystem

• Dr. Lisa W. Griffin (NASA MSFC) for permission to use the Huber meanlinecodes

NASA Fundamental Aeronautics program Subsonic Rotary Wing project

23

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NASA GRC warm turbine test facility

Turbine Test Article

work platform forsecondary air circuits

air heaters

gearbox

sync.machineflow

flow measurement t Altit d

flow

air supply;40 psig Combustion Air(clean, dry, ambient temperature)

flow measurementventuri

to AltitudeExhaustat 26” Hg

26