A centrifugal compressor requires a wide operating range as well as a high efficiency. At high pressure ratios, the impeller discharge velocity becomes transonic and effective pressure recovery in a vaned or vaneless diffuser is necessary. At high pressure ratios, a vaned diffuser is used as it has high pressure recovery, but may have a narrow operating range. At low flow, diffuser stall may trigger surge. At high flow, choking in the throat of the vanes may limit the maximum flow rate. A low solidity diffuser allows a good pressure recovery because it has vanes to guide the flow and a wide operating range as there is no geometrical throat to limit the maximum flow. In experimental studies at a pressure ratio around 4:1, the author has replaced vaned diffusers with a range of low solidity diffusers to try to broaden the operating range. The test results showed that the low solidity diffuser also chokes. In this paper, a virtual throat is defined and its existence is confirmed by flow visualization and pressure measurements. A method to select low solidity diffusers is proposed based on test data and the fundamental nature of the flow. The extension of the proposed method to the selection of a vaneless diffuser is examined and a design approach for a vaneless diffuser system to minimize surge flow rate without limiting the attainable maximum flow rate is proposed.

References

References
1.
Tamaki
,
H.
,
2015
, “
Experimental Study on Matching of Low Solidity Diffuser With High Pressure Ratio Centrifugal Compressor
,” 7th International Conference on Pumps and Fans (ICPF 2015), Hangzhou, China, Oct. 18–21.
2.
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
.
3.
Casey
,
M.
, and
Rusch
,
D.
,
2014
, “
The Matching of a Vaned Diffuser With a Radial Compressor Impeller and Its Effect on the Stage Performance
,”
ASME J. Turbomach.
,
136
(
12
), p.
121004
.
4.
Casey
,
M. V.
,
Dalbert
,
P.
, and
Shurter
,
E.
,
1990
, “
Radial Compressor Stage for Low Flow Coefficients
,” 4th European Congress on Fluid Machinery for Oil, Petrochemical and Related Industries, The Hague, The Netherlands, May 21–23, IMechE Paper No. C403/004.
5.
Rusch
,
D.
, and
Casey
,
M.
,
2012
, “
The Design Space Boundaries for High Flow Capacity Centrifugal Compressors
,”
ASME
Paper No. GT2012-68105
.
6.
Dixon
,
S. L.
, and
Hall
,
C.
,
2014
,
Fluid Mechanics and Thermodynamics of Turbomachinery
,
7th ed.
,
Butterworth-Heinemann
,
Oxford, UK
, pp.
53
61
: 80–83.
7.
Whitfield
,
A.
, and
Baines
,
N. C.
,
1990
,
Design of Radial Turbomachines
,
Longman Scientific and Technical
,
Harlow, Essex, UK
, pp.
94
99
.
8.
Senoo
,
Y.
,
Hayami
,
H.
, and
Ueki
,
H.
,
1983
, “
Low-Solidity Tandem-Cascade Diffusers for Wide-Flow-Range Centrifugal Blowers
,”
ASME
Paper No. 83-GT-3
.
9.
Osbone
,
C.
, and
Sorokes
,
J.
,
1988
, “
The Application of Low Solidity Diffusers in Centrifugal Compressors
,” Flow in Non-Rotating Turbomachinery Component,
ASME FED
, Vol. 69, pp.
89
101
.
10.
Sorokes
,
J.
,
1995
, “
Industrial Centrifugal Compressors—Design Considerations
,” ASME
Paper No. 95-WA/PID-2
.
11.
Hayami
,
H.
,
Research and Development of a Transonic Turbo Compressor, Turbomachinery Fluid Dynamics and Heat Transfer
,
Marcel Dekker, Inc
,
New York
, pp.
69
77
.
12.
Oh
,
J. S.
, and
Agrawal
,
G. L.
,
2007
, “
Numerical Investigation of Low Solidity Vaned Diffuser Performance in a High-Pressure Centrifugal Compressor Part I: Influence of Vane Solidity
,”
ASME
Paper No. GT2007-27260
.
13.
Tamaki
,
H.
,
Kawakubo
,
T.
,
Unno
,
M.
,
Abe
,
S.
, and
Majima
,
K.
,
2014
, “
Performance Improvement of Multistage Centrifugal Compressor With Low Flow-Rate Stages Based on Factory Acceptance Test Data
,”
ASME
Paper No. GT2014-25156
.
14.
Tamaki
,
H.
, and
Yamaguchi
,
S.
,
2007
, “
The Experimental Study of Matching Between Centrifugal Compressor Impeller and Vaneless Diffusers for Turbochargers
,”
ASME
Paper No. GT2007-28300
.
15.
Denton
,
J. D.
,
1993
, “
Loss Mechanism in Turbomachines
,”
ASME J. Turbomach.
,
115
(
4
), pp.
621
656
.
You do not currently have access to this content.