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National Aeronautics and Space Administration

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Aerodynamic Performance of a Compact, High Work-Factor Centrifugal Compressor

at the Stage and Subcomponent LevelEdward P. Braunscheidel & Gerard E. Welch - NASA Glenn Research Center

Gary J. Skoch – Army Research LaboratoryGorazd Medic and Om P. Sharma – United Technologies Research Center

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50th AIAA/ASME/SAE/ASEE Joint Propulsion ConferenceJuly 28-30, 2014, Cleveland, OH

https://ntrs.nasa.gov/search.jsp?R=20140017398 2020-04-04T01:15:51+00:00Z


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Aerodynamic Performance of a Compact, High Work-FactorCentrifugal Compressor at the Stage and Subcomponent Level

• Background and Scope• Test Article and Facility Description• Key Instrumentation• Stage and Subcomponent Results• Performance Assessment vs. Pre-test CFD• Summary

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Background and Scope

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• NASA/UTRC High Efficiency Centrifugal Compressor (HECC) NRA cost-share contract– Develop HPC technologies for

advanced turboshaft engines for rotorcraft

– Challenging goal set for centrifugal compressors

– Maintain similitude between engine scale and rig scale hardware

– Design/Analysis, fab, assembly, test

Metric Intent (rig scale,2x engine scale) CFD*

Exit-corr. flow 2.1 < �c,ex < 3.1 lbm/s 2.98

Work factor 0.60 < �H0/U22 < 0.75 0.7905

�p,tt (poly) � 0.88 0.888

Diam. ratio Dmax / D2 � 1.45 1.45

Design SM 13% 12%

Mex 0.15 0.15

�ex 15� 14�

*Medic, G., et al., “High Efficiency Centrifugal Compressor for Rotorcraft Applications,” NASA/CR—2014-218114, Sept., 2014.


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HECC Stage OverviewDesign speed = 21,789 ft/s (Exit tip speed = 1615 ft/s)

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– Impeller: 15 blade/splitter pairs, spanwise varying backsweep, lean, elliptical leading and trailing edges

– Diffuser: 20 vane/splitter pairs, with splitters offset to maximize pressure recovery– EGVs: 60 cascade-style airfoils


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Small Engine Component Test Facility (CE-18)

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• 6000 hp / 60,000 rpm / 30:1 PR / Max 20� diameter • Inlet pressures 2-45 psia / Inlet air -20 ºF to ambient• Inlet flow 60 lbm/s / Exhaust to ambient or 26 in-hg

Air supply

Air Exhaust

Inlet Fine Control Valve

Plenum (Station 0, Inlet Reference)

Mass Flow Orifice

Test articleInlet Coarse Control Valve

Gearbox


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Tip Clearance System

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��/b of 0.5%, � 0.12 pt. impact on �tt

Impeller Translates Axially

Tip Clearance Variations @ Nc = 100%

• 4 rub probes at each station used for tip clearance calibration/alignment

• �/b = 2% (0.012�) design tip clearance, no step in flowpath at impeller/diffuser interface

0.0094

0.0111

0.0095

0.0118

0.00900.00960.0127

0.0092

Impeller�TEImpeller�LE


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Diffuser LE and “Rake” Instrumentation

• Vane Leading Edge (2.4)– Two vanes with 7 Kiel head p0 ports – Key measurements for impeller and

diffuser performance

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• Vane Trailing Edge (2.7)– 6 locations resolve one main-to-

main diffuser passage– Miniature Cobras at immersions

of 15-85%, calibrated for � and p0

Passage�APassage�B


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Surveys3-Port Cobra Probe

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• Vaneless Space (2.2) & Diffuser Exit (2.7)– Traversable spanwise, manually aligned to

flow– Calibrated to M=0.84 (Cal. Facility limit)

Station 2.2

Station 2.7


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EGV Exit/Stage Rating (Station 3)• 12 Rakes indexed to resolve one main-to-main diffuser pitch• Kiel head p0 and T0 ports on area centroids

• 3 adjacent EGVs have LE Kiel head p0 (25-75% span)

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po x3

To�x2


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Stage and Subcomponent Results

• Compressor Maps• Design point performance - comparison of measured vs. predicted• Representative subcomponent measurements at Nc = 100%

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Stage Pressure Ratio vs. Inlet Corrected Mass Flow Rate

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1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

4 5 6 7 8 9 10 11 12 13

Total�Pressure�Ra

tio,�p

0,3.0/p 0

,0

Inlet�Corrected�Mass�Flow�Rate,�lbm/s

Stall�Boundary

3.0�lbm/s�op�line

Design Point

105%

100%

95%

90%85%

75%70%


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0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0

Efficiency,�%�

Inlet�Corrected�Mass�Flow�Rate,��lbm/s

Design Intent

Adiabatic

Polytropic

105%100%95%90%85%75%70%

Efficiency vs. Inlet Corrected Mass Flow Rate

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Metric Design�GoalRig�Scale�

Design�Intent�p0,0=14.7�psia

Rig�Scale��Design�Intent�

p0,0=11�psia

Measuredp0,0=11�psia

Uncertainty�(95%�Confidence)

Pressure�ratio,��p0,3/p0,0 4.85 4.80 4.68�± 0.0074

Inlet�flow�rate,��c,in ,�lbm/s 11.2 11.1 10.85�± 0.1

Exit flow�rate,��c,ex ,�lbm/s 2.1�<��c,ex <�3.1 2.98 2.98 2.98

Adiabatic�efficiency�, �tt ,��% 0.862 0.8495 0.822�± 0.011

Polytropic efficiency, �p,tt ,�% > 0.88 0.888 0.879 0.855

Adiabatic,�total�pressure�to�static�pressure,��ts , %

0.852 0.8396 0.805

Exit�Mach�number,��Mex 0.15 0.15 0.15 0.18

Exit�flow�angle,��ex ,�deg 15o 14o 14o 34.3o

Stability�Margin,��SM,��% 13 12 12 7.5

Work factor 0.60�<��H0/U22 <�0.75 0.7905 0.793 0.81

Diameter�ratio Dmax/D2 < 1.45 1.45 1.45 1.45

Measured vs. Predicted Performance(Nc = 100%, �c,ex = 3.0 lbm/s, design tip clearance)

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Impeller Exit (2.2) and Diffuser Vane LE (2.4)(Nc = 100%, �c,ex = 3.0 lbm/s)

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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

50 60 70 80 90 100

Fractio

n�of�sp

an�from

�hub

Swirl�angle��2.2,�deg.

100% Nc

Probe�at�2.2

Pre�test�CFD

• Measured swirl angle in relatively good agreement

• Vane to vane agreement very good• Vane LE and CFD in good agreement• Probe p0 (at 2.2) lower than vane LE, probe does not

adequately resolve the pressure flow field • Probe (2.2 vaneless space) data only used qualitatively

ur

u�

�u

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

3 3.5 4 4.5 5 5.5 6

Fractio

n�of�sp

an�from

�hub

Local�p0,2.2(z)/p0,0

100% Nc

Probe�at�2.2

Vane�LE�

Pre�test�CFD


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Diffuser Exit Probe Survey Data (2.7)(Nc = 100%, �c,ex = 3.0 lbm/s)

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�

B

p0,2.7/p0,0

Flow�Angle,�Deg.

SS��PSsplitter

SS��PSmain

PSmain

SS��PSsplitter

SS��PSmain

%�Span�Hub�to�Tip

%�Pitch,�Main�to�Main

%�Span�Hub�to�Tip

A

TE�Mean�Camber�AngleMain�=�51�degSplitter�=�52�deg

0%

100% 200%

100%

0%

ur

u�

�u

AB


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Diffuser Exit Survey Results vs. Operating Condition (Nc = 100%, Choke, Design, Near-Stall)

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• Flow redistributes as stage is throttled• High swirl angles at SS main vane could indicate

separated flow


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Pressure Contours at Stations 2.7, 2.8, 3.0(Nc = 100%, �c,ex = 3.0 lbm/s)

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po,x/po,0


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Diffuser Vanes Loading Diagrams-Shroud Static Pressures (Nc=100, near design point CFD)

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2.5

3

3.5

4

4.5

5

Normalize

d�static�pressure,�p/p

0,0

1.5

2

2.5

3

3.5

4

4.5

5

8.5 9 9.5 10 10.5 11 11.5

Normalize

d�static�pressure,�p/p

0,0

Radius,�in.

Pressure�side��pre�test�CFDSuction�side��pre�test�CFDPressure�side��dataSuction�side��data

AB

SS Main

PS Main

PS Splitter

SS Splitter

• Overall pressure rise lower than predicted• Negative loading on splitter indicates

operating at large negative incidence vs. lightly loaded design intent


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60

65

70

75

80

85

90

95

10 10.5 11 11.5 12 12.5

Impe

ller�a

nd�stage�efficiency,�%

Inlet�corrected�flow,�lbm/s

Impeller�(Sta.�0�to�2.4)Stage�(Sta.�0�to�3)Impeller��pre�test�CFDStage��pre�test�CFD

Stage and Impeller Adiabatic Efficiency

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100% Nc

Impeller CFD

Stage CFD


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Diffusion System Static Pressure Rise

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�0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

10 10.5 11 11.5 12

Static�pressure�rise�coefficient


Diffuser90�deg.�bend�+�EGVDiffuser�+�90�deg.�bend�+�EGV

100% Nc

Design�intent�(�c,ex =�3�lbm/s)

Stall

Choke

• Static pressure rise increases from choke to stall (Diffuser and Diffuser+Bend+EGV)

• Static pressure rise across 90� bend and EGV is relatively constant

� � inininexp ppppc � ,0/


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Diffuser Loss Bucket

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0

5

10

15

20

25

30

35

10 10.5 11 11.5 12 12.5

�p 0/p

0of�diffuser,�%



100% Nc

Expt.stall�boundary

Data

CFD

Test results show a minimum loss at a lower flow rate than design intent


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Diffuser Corrected Flow Characteristic

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2

2.2

2.4

2.6

2.8

3

3.2

2 2.5 3 3.5 4

Impe

ller�e

xit�corrected

�flow

,�lb m

/s

Stage�exit�corrected,�lbm/s

NASA�HECC�12�mil��coarse�grid��mixing�planeNASA�HECC�12�mil��fine�grid��mixing�planeHECC�test�data

Design�intent�100% Nc

Diffuser processes flow as per design intent @ �c,ex=3.0 lbm/s


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Impeller Corrected Flow Characteristic

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2

2.2

2.4

2.6

2.8

3

3.2

10 10.5 11 11.5 12 12.5

Impe

ller�e

xit�corrected

�flow

,�lb m

/s

Stage�(impeller)�inlet�corrected�flow,�lbm/s

Data CFD


100% Nc

• Impeller is operating at a lower �c,in at the design intent impeller exit correct flow rate


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Summary

• Aerodynamic performance of an advanced, compact, high work-factor centrifugal compressor stage was presented

• Stage performance and stability were lower than design intent– Adiabatic Efficiency by 2.75 pts., mass flow by 2.25%, and

Stability Margin by 4.5 pts. • Differences in predicted and measured impeller efficiency,

impeller flow characteristics, and diffuser loss buckets were observed.

• Root-cause-analysis of the performance shortfall was initiated within the NRA contract. Analyses continue with intent to guide future design efforts.

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Comprehensive data sets and geometry to be made publically available


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Acknowledgements

Drs. Joo JongwookLarry HardinDuane McCormickWilliam CousinsBrian HolleyPaul Van SlootenElizabeth LurieAamir Shabbir

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Dr. Michael HathawayMark StevensJonathon MitchelJozsef PuskasAdam ReddingDavid HayduRichard Senyitko

Design Review Team

aerodynamic performance of a compact, high work-factor ... · • aerodynamic performance of an...

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