Variable inlet prewhirl is an effective way to suppress compressor flow instability. Compressors usually employ a high degree of positive inlet prewhirl to shift the surge line in the performance map to a lower mass flow region. However, the efficiency of a compressor at high inlet prewhirl is far lower than that at zero or low prewhirl. This paper investigates the performances of a centrifugal compressor with different prewhirls, discusses the mechanisms which are responsible for the production of extra loss induced by high inlet prewhirl and develops flow control methods to improve efficiency at high inlet prewhirl. The approach combines steady three-dimensional Reynolds average Navier–Stokes (RANS) simulations with theoretical analysis and modeling. In order to make the study universal to various applications with inlet prewhirl, the inlet prewhirl was imposed by modifying the velocity direction of inlet boundary condition. Simulation results show that the peak efficiency at high inlet prewhirl is reduced by over 7.6% points compared with that at zero prewhirl. The extra loss occurs upstream and downstream of the impeller. Severe flow separation, which reduces efficiency by 2.3% points, was found near the inlet hub. High inlet prewhirl works like a centrifuge gathering low-kinetic-energy fluid to hub, which induces the separation. A dimensionless parameter C was defined to measure the centrifugal trend of gas and indicate the flow separation near the inlet hub. As for the extra loss which is produced downstream of the impeller, the flow mismatch of impeller and diffuser at high prewhirl causes a violent backflow near the diffuser vanes' leading edges. An analytical model was built to predict diffuser choking mass flow. It proves that the diffuser has already operated unstably at high prewhirl. Based on these two loss mechanisms, the hub curve and the diffuser stager angle were modified and adjusted, respectively, for higher efficiency at high prewhirl. The efficiency improvement benefited from the modification of the hub is 1.1% points, and that benefited from the combined optimization is 2.4% points. During optimizing, constant distribution of inlet prewhirl was found to be another factor for inducing reverse flow at the leading edge of the impeller blade root, which turned out being blamed on the misalignment of the swirl angle and the blade angle.

References

References
1.
Botros
,
K. K.
, and
Henderson
,
J. F.
,
1994
, “
Developments in Centrifugal Compressor Surge Control—A Technology Assessment
,”
ASME J. Turbomach.
,
116
(
2
), pp.
240
249
.
2.
Lown
,
H.
, and
Wiesner
,
F. J.
,
1959
, “
Prediction of Choking Flow in Centrifugal Impellers
,”
ASME J. Basic Eng.
,
81
(1), pp.
29
36
.
3.
Wallace
,
F. J.
,
Whitfield
,
A.
, and
Atkey
,
R. C.
,
1975
, “
Experimental and Theoretical Performance of a Radial Flow Turbocharger Compressor With Inlet Prewhirl
,”
Proc. Inst. Mech. Eng. Part D
,
189
(
1
), pp.
177
186
.
4.
Simon
,
H.
,
Wallmann
,
T.
, and
Monk
,
T.
,
1987
, “
Improvements in Performance Characteristics of Single-Stage and Multistage Centrifugal Compressors by Simultaneous Adjustments of Inlet Guide Vanes and Diffuser Vanes
,”
ASME J. Turbomach.
,
109
(
1
), pp.
41
47
.
5.
Rodgers
,
C.
,
1991
, “
Centrifugal Compressor Inlet Guide Vanes for Increased Surge Margin
,”
ASME J. Turbomach.
,
113
(
4
), pp.
696
702
.
6.
Coppinger
,
M.
, and
Swain
,
E.
,
2000
, “
Performance Prediction of an Industrial Centrifugal Compressor Inlet Guide Vane System
,”
Proc. Inst. Mech. Eng. Part A
,
214
(
2
), pp.
153
164
.
7.
Mohtar
,
H.
,
Chesse
,
P.
,
Yammine
,
A.
, and
Hetet
,
J. F.
,
2008
, “
Variable Inlet Guide Vanes in a Turbocharger Centrifugal Compressor: Local and Global Study
,”
SAE
Paper No. 2008-01-0301.
8.
Mohseni
,
A.
,
Goldhahn
,
E.
,
Van den Braembussche
,
R. A.
, and
Seume
,
J. R.
,
2012
, “
Novel IGV Designs for Centrifugal Compressors and Their Interaction With the Impeller
,”
ASME J. Turbomach.
,
134
(
2
), p.
021006
.
9.
Kyrtatos
,
N.
, and
Watson
,
N.
,
1980
, “
Application of Aerodynamically Induced Prewhirl to a Small Turbocharger Compressor
,”
ASME J. Eng. Gas Turbines Power
,
102
(
4
), pp.
943
950
.
10.
Whitfield
,
A.
, and
Abdullah
,
A. H.
,
1998
, “
The Performance of a Centrifugal Compressor With High Inlet Prewhirl
,”
ASME J. Turbomach.
,
120
(
3
), pp.
487
493
.
11.
Galindo
,
J.
,
Serrano
,
J. R.
,
Margot
,
X.
,
Tiseira
,
A.
,
Schorn
,
N.
, and
Kindl
,
H.
,
2007
, “
Potential of Flow Pre-Whirl at the Compressor Inlet of Automotive Engine Turbochargers to Enlarge Surge Margin and Overcome Packaging Limitations
,”
Int. J. Heat Fluid Flow
,
28
(
3
), pp.
374
387
.
12.
Rodgers
,
C.
,
1977
, “
Impeller Stalling as Influenced by Diffusion Limitations
,”
ASME J. Fluids Eng.
,
99
(
1
), pp.
84
93
.
13.
Chen
,
Y. N.
,
Hagelstein
,
D.
,
Kassens
,
I.
,
Hasemann
,
H.
,
Haupt
,
U.
, and
Rautenberg
,
M.
,
1999
, “
Overshoot of the Rankine Vortex Formed in the Flow Field Behind the Inlet Guide Vane of Centrifugal Compressors
,”
ASME
Paper No. 99-GT-182.
14.
Jameson
,
A.
, and
Baker
,
T. J.
,
1984
, “
Multigrid Solution of the Euler Equations for Aircraft Configurations
,”
AIAA
Paper No. 84-0093.
15.
Jameson
,
A.
,
Schmidt
,
W.
, and
Turkel
,
E.
,
1981
Numerical Solutions of the Euler Equations by Finite Volume Methods Using Runge–Kutta Time-Stepping Schemes
,”
AIAA
Paper No. 81-1259.
16.
Spalart
,
P.
, and
Allmaras
,
S.
,
1992
, “
A One Equation Turbulence Model for Aerodynamic Flows
,”
AIAA
Paper No. 92-0439.
17.
Krain
,
H.
,
Hoffmann
,
B.
, and
Pak
,
H.
,
1995
, “
Aerodynamics of a Centrifugal Compressor Impeller With Transonic Inlet Conditions
,”
ASME
Paper No. 95-GT-079.
18.
Eisenlohr
,
G.
,
Krain
,
H.
,
Richter
,
F.-A.
, and
Tiede
,
V.
,
2002
, “
Investigations of the Flow Through a High Pressure Ratio Centrifugal Impeller
,”
ASME
Paper No. GT2002-30394.
19.
NUMECA
,
2010
, “
NUMECA FINE/Turbo User Manual 8.7
,” NUMECA International, Brussels, Belgium, http://www.numeca.com
20.
Zheng
,
X. Q.
,
Huenteler
,
J.
,
Yang
,
M. Y.
,
Zhang
,
Y. J.
, and
Bamba
,
T.
,
2010
, “
Influence of the Volute on the Flow in a Centrifugal Compressor of a High-Pressure Ratio Turbocharger
,”
Proc. Inst. Mech. Eng. Part A
,
224
(
8
), pp.
1157
1169
.
21.
Denton
,
J. D.
,
1993
, “
The 1993 IGTI Scholar Lecture: Loss Mechanisms in Turbomachines
,”
ASME J. Turbomach.
,
115
(
4
), pp.
621
656
.
22.
Cumpsty
,
N. A.
,
2004
,
Compressor Aerodynamics
,
Kreiger Publishing Company
,
Malabar, FL
, p.
99
.
23.
Greitzer
,
E. M.
,
Tan
,
C. S.
, and
Graf
,
M. B.
,
2004
,
Internal Flow: Concepts and Applications
,
Cambridge University Press
, New York, p.
57
.
24.
Tamaki
,
H.
,
Nakao
,
H.
, and
Saito
,
M.
,
1999
, “
The Experimental Study of Matching Between Centrifugal Compressor Impeller and Diffuser
,”
ASME J. Turbomach.
,
121
(
1
), pp.
113
118
.
You do not currently have access to this content.