The current centrifugal compressor design for the oil & gas market is more and more challenging, and the presence of many competitors is pushing technology towards both a casing size reduction and a rotational speed increase. The first point is leading to an increase in the number of wheels per rotor (to do the same service), and the second point is forcing to cross two or even three rotor modes (hence a higher control of rotor damping is necessary). The two points together are leading to increase the rotor “flexibility ratio” (defined as the ratio between the maximum continuous speed and the first critical speed at infinite support stiffness according to API standard, and finally the rotordynamic stability is very much challenged. The centrifugal compressor's rotordynamic stability is strongly related to the internal seals' dynamic behavior, and for this reason, the authors' company decided several years ago to develop internally a high pressure seal test rig to measure internal seals stiffness and damping. The rig is now in operation, and in a previous paper the authors described its main capabilities, the applied identification procedures, and the preliminary test results captured for a long labyrinth seal (smooth rotor, straight toothed stator) tested up to 200 bar. This paper is intended to show more data for the same long Laby with special focus on some peculiar test as negative preswirl test, single frequency versus multifrequency test, offset versus centered seal test. The negative preswirl test shows a drastic change in the effective damping (from destabilizing to stabilizing) and provides a support in favor of the selection of swirl reversal devices at seals upstream. The multifrequency excitation test approach (based on the concurrent presence of several frequencies not multiples at each other) is compared with a single frequency excitation providing similar results and thus confirming the soundness of the multiple effects linear superimposition assumption. The effect of a static offset (simulating the real position of a rotor inside an annular seal) is also investigated proving that the relevant impact is negligible within the range of eccentricity explored (10% of seal clearance). Moreover, a pocket damper seal (PDS) with the same nominal diameter, clearance, and effective length has been tested (up to 300 bar) and compared with the Laby. As expected, the PDS shows both a higher effective stiffness and damping at the same test conditions, so the promising results already collected in a previous test campaign which was performed on a smaller scale and lower pressure test rig were mostly confirmed with the only exception for the effective damping crossover frequency which was lower than expected.

References

References
1.
Smith
,
K. J.
,
1975
, “
An Operation History of Fractional Frequency Whirl
,”
Proceedings of the 4th Turbomachinery Symposium, Turbomachinery Laboratory
,
Texas A&M University
,
College Station, TX
, October 14–16, pp.
115
125
.
2.
Cochrane
,
1976
, “
New Generation Compressor Injecting Gas at Ekofisk
,”
OilGas J.
,
74
, pp.
63
70
.
3.
Iwatsubo
,
T.
,
Takahara
,
K.
, and
Kawai
,
R.
,
1984
, “
A New Model of Labyrinth Seal for Prediction of the Dynamic Force
,” Rotordynamic Instability Problems in High-Performance Turbomachinery, College Station, TX, May 28–30.
4.
Childs
,
D.
, and
Scharrer
,
J.
,
1986
, “
An Iwatsubo Based Solution for Labyrinth Seals: Comparison to Experimental Results
,”
ASME J. Eng. Gas Turbine Power
,
108
(2), pp.
325
331
.10.1115/1.3239907
5.
Picardo
,
A.
, and
Childs
,
D.
,
2005
, “
Rotordynamic Coefficients for a Teeth-on-Stator Labyrinth Seals at 70 bar Supply Pressures: Measurements Versus Theory and Comparisons to a Hole-Pattern Stator Seal
,”
ASME J. Eng. Gas Turbines and Power
,
127
(4), pp.
843
855
.10.1115/1.1924634
6.
Wagner
,
N. G.
, and
Steff
,
K.
,
1996
, “
Dynamic Labyrinth Coefficients From a High Pressure Full Scale Test Rig Using Magnetic Bearings
,” Rotordynamic Instability Problems in High-Performance Turbomachinery, College Station, TX, May 6–8,
NASA Conference Publication No. 3344
, pp.
95
112
.
7.
Wagner
,
N. G.
,
Steff
,
K.
,
Gausmann
,
R.
, and
Schmidt
,
M.
,
2009
, “
Investigations on the Dynamic Coefficients of Impeller Eye Labyrinth Seals
,”
Proceedings of the 38th Turbomachinery Symposium, Turbomachinery Laboratory
,
Texas A&M University
,
College Station, TX
, September 14–17, pp.
53
70
.
8.
Baumann
,
U.
,
1999
, “
Rotordynamic Stability Test on High Pressure Radial Compressors
,”
Proceedings of the 28th Turbomachinery Symposium, Turbomachinery Laboratory
,
Texas A&M University
,
College Station, TX
, September 12–15, pp.
115
122
.
9.
Moore
,
J.
,
Walker
,
S.
, and
Kuzdzal
,
M.
,
2002
, “
Rotordynamic Stability Measurement During Full Load
,”
Proceedings of the 31st Turbomachinery Symposium, Turbomachinery Laboratory
,
Texas A&M University
,
College Station, TX
, September 9–12, pp.
29
38
.
10.
Camatti
,
M.
,
Vannini
,
G.
,
Fulton
,
J. W.
, and
Hopenwasser
,
F.
,
2003
, “
Instability of a High Pressure Compressor Equipped With Honeycomb Seals
,”
Proceedings of the 32nd Turbomachinery Symposium, Turbomachinery Laboratory
,
Texas A&M University
,
College Station, TX
, September 8–11, pp.
39
48
.
11.
Kocur
,
J.
,
Nicholas
,
J.
, and
Lee
,
C.
,
2007
, “
Surveying Tilting Pad Journal Bearing and Gas Labyrinth Seal Coefficients and Their Effect on Rotor Stability
,”
Proceedings of the 36th Turbomachinery Symposium, Turbomachinery Laboratory
,
Texas A&M University
,
College Station, TX
, September 11–13, pp.
1
10
.
12.
API Standard 617 (R2009)
, July 2002, “Axial and Centrifugal Compressors and Expander-Compressors for Petroleum, Chemical and Gas Service Industry,” 7th ed., American Petroleum Institute, Washington, DC.
13.
Vannini
,
G.
,
Cioncolini
,
S.
,
Calicchio
,
V.
, and
Tedone
,
F.
,
2011
, “
Development of an Ultra-High Pressure Rotordynamic Test Rig for Centrifugal Compressors Internal Seals Characterization
,”
Proceedings of the 40th Turbomachinery Symposium, Turbomachinery Laboratory
,
Texas A&M University
,
College Station, TX
, September 12–15, pp.
46
59
.
14.
Ertas
,
B.
,
Delgado
,
A.
, and
Vannini
,
G.
,
2012
, “
Rotordynamic Force Coefficients for Three Types of Annular Gas Seals With Inlet Preswirl and High Differential Pressure Ratio
,”
ASME J. Eng. Gas Turbine Power
,
134
(4), p.
042503
.10.1115/1.4004537
15.
Picardo
,
A.
,
2003
, “
High Pressure Testing of See-Through Labyrinth Seals
,” Masters thesis, Texas A&M University, College Station, TX.
16.
Kirk
,
G.
, and
Simpson
,
M.
,
1985
, “
Full Load Shop Testing of 18000 hp Gas Turbine Driven Centrifugal Compressor for Offshore Platform Service: Evaluation of Rotor Dynamics Performance
,”
NASA Conference Publication 2409, Proceeding of Instability in Rotating Machinery Symposium
,
Carson City, NV
, June 10–14.
17.
Brown
,
P.
, and
Childs
,
D.
,
2012
, “
Measurement Versus Predictions of Rotordynamic Coefficients of a Hole-Pattern Gas Seal With Negative Preswirl
,”
ASME J. Eng. Gas Turbine Power
,
134
(
12
), p.
122503
.10.1115/1.4007331
18.
Thorat
,
M.
, and
Childs
,
D.
,
2009
, “
Predicted Rotordynamic Behavior of a Labyrinth Seal as Rotor Surface Velocity Approaches Mach 1
,”
Proceedings of ASME International Gas Turbine Institute
,
Turbo Expo
,
Orlando, FL
, June 8–12,
ASME
Paper No. GT2009-59256.10.1115/GT2009-59256
19.
Rouvas
,
C.
, and
Childs
,
D.
,
1993
, “
A Parameter Identification Method for the Rotordynamic Coefficients of a High Reynolds Number Hydrostatic Bearing
,”
ASME J. Vibr. Acoust.
,
115
(3), pp.
264
270
.10.1115/1.2930343
20.
Childs
,
D.
, and
Hale
,
K.
,
1994
, “
A Test Apparatus and Facility to Identify the Rotordynamic Coefficients of High-Speed Hydrostatic Bearings
,”
ASME J. Tribol.
,
116
(2), pp.
337
344
.10.1115/1.2927226
21.
Holt
,
C.
, and
Childs
,
D.
,
2002
, “
Theory Versus Experiment Results for the Dynamic Impedances of Two Hole-Pattern Annular Gas Seals
,”
ASME J. Tribol.
,
124
(1), pp.
137
143
.10.1115/1.1398297
22.
Weatherwax
,
M.
, and
Childs
,
D.
,
2003
, “
Theory Versus Experiment for the Rotordynamic Characteristics of a High Pressure Honeycomb Annular Gas Seal at Eccentric Positions
,”
ASME J. Tribol.
,
125
(2), pp.
422
429
.10.1115/1.1504093
23.
Nielsen
,
K. K.
, and
Underbakke
,
H.
,
2012
, “
Hole-Pattern and Honeycomb Seal Rotordynamic Forces: Validation of CFD-Based Prediction Techniques
,”
Proceedings of ASME International Gas Turbine Institute
,
Turbo Expo
,
Copenhagen, Denmark
, June 11–15.
ASME
Paper No. GT2012-69878.10.1115/GT2012-69878
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