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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

A Systematic Approach to Estimate the Impact of the Aerodynamic Force Induced by Rotating Stall in a Vaneless Diffuser on the Rotordynamic Behavior of Centrifugal Compressors

[+] Author and Article Information
Alessandro Bianchini

e-mail: bianchini@vega.de.unifi.it

Davide Biliotti

e-mail: biliotti@vega.de.unifi.it

Giovanni Ferrara

e-mail: giovanni.ferrara@unifi.it
Department of Industrial Engineering,
University of Florence,
Via di Santa Marta 3,
Firenze 50139, Italy

Lorenzo Ferrari

CNR-ICCOM,
National Research Council of Italy,
Via Madonna del Piano 10,
Sesto Fiorentino 50019, Italy
e-mail: lorenzo.ferrari@iccom.cnr.it

Elisabetta Belardini

e-mail: elisabetta.belardini@ge.com

Marco Giachi

e-mail: marco.giachi@ge.com

Libero Tapinassi

e-mail: libero.tapinassi@ge.com

Giuseppe Vannini

e-mail: giuseppe.vannini@ge.com
GE Oil & Gas,
Via Felice Matteucci 2,
Florence 50127, Italy

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 17, 2013; final manuscript received July 22, 2013; published online September 17, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(11), 112502 (Sep 17, 2013) (9 pages) Paper No: GTP-13-1170; doi: 10.1115/1.4025065 History: Received June 17, 2013; Revised July 22, 2013

One of the main challenges of the present industrial research on centrifugal compressors is the need for extending the left margin of the operating range of the machines. As a result, interest is being paid to accurately evaluating the amplitude of the pressure fluctuations caused by rotating stall, which usually occurs prior to surge. The related aerodynamic force acting on the rotor can produce subsynchronous vibrations, which can prevent the machine's further operation, in case their amplitude is too high. These vibrations are often contained due to the stiffness of the oil journals. Centrifugal compressor design is, however, going towards alternative journal solutions having lower stiffness levels (e.g., active magnetic bearings or squeeze film dampers), which will be more sensitive to this kind of excitation: consequently, a more accurate estimation of the expected forces in the presence of dynamic external forces such as those connected to an aerodynamically unstable condition is needed to predict the vibration level and the compressor operability in similar conditions. Within this scenario, experimental tests were carried out on industrial impellers operating at high peripheral Mach numbers. The dedicated test rig was equipped with several dynamic pressure probes that were inserted in the gas flow path; moreover, the rotor vibrations were constantly monitored with typical vibration probes located near the journal bearings. The pressure field induced by the rotating stall in the vaneless diffuser was reconstructed by means of an ensemble average approach, thus defining the amplitude and frequency of the external force acting on the impeller. The calculated force value was then included in the rotordynamic model of the test rig: the predicted vibrations on the bearings were compared with the measurements, showing satisfactory agreement. Moreover, the procedure was applied to two real multistage compressors, showing notable prediction capabilities in the description of rotating stall effects on the machine rotordynamics. Finally, the prospects of the proposed approach are discussed by investigating the response of a real machine in high-pressure functioning when different choices of journal bearings are made.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Schematic view of the tested configuration

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Fig. 2

Circumferential positioning of the dynamic pressure sensors

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Fig. 3

Joint time-frequency graph of the test

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Fig. 4

Evolution of the area subtended to the stall frequency versus the flow coefficient

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Fig. 5

Power spectrum of the pressure probes at Section 20 at the beginning of the analysis window

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Fig. 6

Pressure signal of Probe 1 at Section 20 and its autocorrelation function

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Fig. 7

Pressure signals of Probes 1 and 2 at Section 20 and their cross correlation function

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Fig. 8

Calculated circumferential pressure distribution due to rotating stall (with standard deviation)

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Fig. 9

Polar representation of the single-lobe stall pattern

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Fig. 10

The rotor's numerical model and mechanical drawing

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Fig. 11

Comparison between the experimental power spectrum of the vibration probe near the impeller and the predicted value using the rotordynamic model

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Fig. 12

Measured vibrations of the whole compressor during the experimental tests

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Fig. 13

Comparison between the determined vibrations and experiments (vibration probe nearest to the impeller)

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Fig. 14

Predicted vibrations in the real compressor at the nearest bearing to the stalling impeller with conventional journal bearings

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Fig. 15

Predicted vibrations in the real compressor at the nearest bearing to the stalling impeller with SFDs

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