The measured aerodynamic performance of a compact, high work factor, single-stage centrifugal compressor, comprising an impeller, diffuser, 90-bend, and exit guide vane (EGV), is reported. Performance levels are based on steady-state total-pressure and total-temperature rake and angularity-probe data acquired at key machine rating planes during recent testing at NASA Glenn Research Center. Aerodynamic performance at the stage level are reported for operation between 70 to 105 of design corrected speed, with subcomponent (impeller, diffuser, and exitguide-vane) detailed flow field measurements presented and discussed at the 100 design-speed condition. Individual component losses from measurements are compared with pre-test predictions on a limited basis

Braunscheidel, Edward P.

Medic, Gorazd

Sharma, Om P.

Skoch, Gary J.

Welch, Gerard E.

The measured aerodynamic performance of a compact, high work-factor, single-stage centrifugal compressor, comprising an impeller, diffuser, 90-bend, and exit guide vane is reported. Performance levels are based on steady-state total-pressure and total-temperature rake and angularity-probe data acquired at key machine rating planes during recent testing at NASA Glenn Research Center. Aerodynamic performance at the stage level is reported for operation between 70 to 105% of design corrected speed, with subcomponent (impeller, diffuser, and exit-guide-vane) flow field measurements presented and discussed at the 100% design-speed condition. Individual component losses from measurements are compared with pre-test CFD predictions on a limited basis

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

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Aerodynamic Performance of a Compact, 
High Work-Factor Centrifugal Compressor 
at the Stage and Subcomponent Level
Edward P. Braunscheidel & Gerard E. Welch - NASA Glenn Research Center
Gary J. Skoch – Army Research Laboratory
Gorazd Medic and Om P. Sharma – United Technologies Research Center
1
50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference
July 28-30, 2014, Cleveland, OH
https://ntrs.nasa.gov/search.jsp?R=20140017398 2019-08-31T14:54:50+00:00Z
National Aeronautics and Space Administration
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Aerodynamic Performance of a Compact, High Work-Factor
Centrifugal 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
2
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Background and Scope
3
• 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.
National Aeronautics and Space Administration
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HECC Stage Overview
Design speed = 21,789 ft/s   (Exit tip speed = 1615 ft/s)
4
– 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)
5
• 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 article
Inlet Coarse 
Control Valve
Gearbox
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Tip Clearance System
6
/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
ImpellerTE
ImpellerLE
National Aeronautics and Space Administration
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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
7
• 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 
PassageAPassageB
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Surveys
3-Port Cobra Probe
8
• 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)
9
po x3
Tox2
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Stage and Subcomponent Results
• Compressor Maps
• Design point performance - comparison of measured vs. predicted
• Representative subcomponent measurements at Nc = 100% 
10
National Aeronautics and Space Administration
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Stage Pressure Ratio vs. Inlet Corrected 
Mass Flow Rate
11
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
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p
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InletCorrectedMassFlowRate,lbm/s
StallBoundary
3.0lbm/sopline
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
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%

InletCorrectedMassFlowRate,lbm/s
Design Intent
Adiabatic
Polytropic
105%100%95%90%85%75%70%
Efficiency vs. Inlet Corrected Mass Flow Rate
12
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Metric DesignGoal
RigScale
DesignIntent
p0,0=14.7psia
RigScale
Design
Intent
p0,0=11psia
Measured
p0,0=11psia
㼼Uncertainty
(95%Confidence)
Pressureratio,p0,3/p0,0 4.85 4.80 4.68± 0.0074
Inletflowrate, c,in ,lbm/s 11.2 11.1 10.85± 0.1
Exit flowrate, c,ex ,lbm/s 2.1< c,ex <3.1 2.98 2.98 2.98
Adiabaticefficiency, tt ,% 0.862 0.8495 0.822± 0.011
Polytropic efficiency, p,tt ,% > 0.88 0.888 0.879 0.855
Adiabatic,totalpressuretostatic
pressure,ts , %
0.852 0.8396 0.805
ExitMachnumber,Mex 0.15 0.15 0.15 0.18
Exitflowangle,ex ,deg 15o 14o 14o 34.3o
StabilityMargin,SM,% 13 12 12 7.5
Work factor 0.60<H0/U22 <0.75 0.7905 0.793 0.81
Diameterratio 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)
13
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Impeller Exit (2.2) and Diffuser Vane LE (2.4)
(Nc = 100%, c,ex = 3.0 lbm/s)
14
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
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Swirlangle2.2,deg.
100% Nc
Probeat2.2
PretestCFD
• 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
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Localp0,2.2(z)/p0,0
100% Nc
Probeat2.2
VaneLE
PretestCFD
National Aeronautics and Space Administration
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Diffuser Exit Probe Survey Data (2.7)
(Nc = 100%, c,ex = 3.0 lbm/s)
15

B
p0,2.7/p0,0
FlowAngle,Deg.
SSPS
splitter
SSPS
main
PS
main
SSPS
splitter
SSPS
main
%Span
HubtoTip
%Pitch,MaintoMain
%Span
HubtoTip
A
TEMeanCamberAngle
Main=51deg
Splitter=52deg
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)
16
• Flow redistributes as stage is throttled
• High swirl angles at SS main vane could indicate 
separated flow
National Aeronautics and Space Administration
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Pressure Contours at Stations 2.7, 2.8, 3.0
(Nc = 100%, c,ex = 3.0 lbm/s)
17
po,x/po,0
National Aeronautics and Space Administration
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Diffuser Vanes Loading Diagrams-Shroud 
Static Pressures (Nc=100, near design point CFD)
18
2.5
3
3.5
4
4.5
5
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p
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1.5
2
2.5
3
3.5
4
4.5
5
8.5 9 9.5 10 10.5 11 11.5
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p
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Radius,in.
PressuresidepretestCFD
SuctionsidepretestCFD
Pressuresidedata
Suctionsidedata
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
I
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%
Inletcorrectedflow,lbm/s
Impeller(Sta.0to2.4)
Stage(Sta.0to3)
ImpellerpretestCFD
StagepretestCFD
Stage and Impeller Adiabatic Efficiency
19
100% Nc
Impeller CFD
Stage CFD
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Diffusion System Static Pressure Rise
20
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
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Inletcorrectedflow,lbm/s
Diffuser
90deg.bend+EGV
Diffuser+90deg.bend+EGV
100% Nc
Designintent
(c,ex =3lbm/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 
21
0
5
10
15
20
25
30
35
10 10.5 11 11.5 12 12.5

p
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%
Inletcorrectedflow,lbm/s
Designintent
(c,ex =3lbm/s)
100% Nc
Expt.
stallboundary
Data
CFD
Test results show a minimum loss at 
a lower flow rate than design intent
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Diffuser Corrected Flow Characteristic
22
2
2.2
2.4
2.6
2.8
3
3.2
2 2.5 3 3.5 4
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Stageexitcorrected,lbm/s
NASAHECC12milcoarsegridmixingplane
NASAHECC12milfinegridmixingplane
HECCtestdata
Designintent
100% Nc
Diffuser processes flow as per 
design intent @ c,ex=3.0 lbm/s
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Impeller Corrected Flow Characteristic
23
2
2.2
2.4
2.6
2.8
3
3.2
10 10.5 11 11.5 12 12.5
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Stage(impeller)inletcorrectedflow,lbm/s
Data CFD
Designintent
(c,ex =3lbm/s)
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. 
24
Comprehensive data sets and geometry to be made publically 
available
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Acknowledgements
Drs. Joo Jongwook
Larry Hardin
Duane McCormick
William Cousins
Brian Holley
Paul Van Slooten
Elizabeth Lurie
Aamir Shabbir
25
Dr. Michael Hathaway
Mark Stevens
Jonathon Mitchel
Jozsef Puskas
Adam Redding
David Haydu
Richard Senyitko
Design Review Team


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

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