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Research Papers

Experimental Analysis of the Pressure Field Inside a Vaneless Diffuser From Rotating Stall Inception to Surge

[+] Author and Article Information
Alessandro Bianchini

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

Davide Biliotti

GE Oil & Gas,
Via Felice Matteucci 10,
Firenze 50127, Italy
e-mail: davide.biliotti@ge.com

Dante Tommaso Rubino

GE Oil & Gas,
Via Felice Matteucci 10,
Firenze 50127, Italy
e-mail: dantetommaso.rubino@ge.com

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

Giovanni Ferrara

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

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received June 22, 2015; final manuscript received June 30, 2015; published online September 16, 2015. Editor: Kenneth C. Hall.

J. Turbomach 137(11), 111007 (Sep 16, 2015) (10 pages) Paper No: TURBO-15-1117; doi: 10.1115/1.4031354 History: Received June 22, 2015; Revised June 30, 2015

An accurate estimation of rotating stall is one of the key points for high-pressure centrifugal compressors, as it is often connected with the onset of detrimental subsynchronous vibrations which can prevent the machine from operating beyond this limit. With particular reference to vaneless diffuser rotating stall, the most common practice in industrial machines is to make use of a limited number of dynamic pressure probes to reconstruct the stall characteristics after an ensemble averaging approach. In this study, a 1:1 model of an industrial compressor stage was tested in a dedicated test rig and equipped with 24 pressure probes properly distributed along the diffuser circumference with the scope of providing a real-time visualization of the spatial pressure distribution within the diffuser. The results allowed the assessment of some important characteristics of the stall cells that were historically supposed based on averaged data, e.g., the cells rigidity. Moreover, the present study confirmed the existence of a stall pattern with two almost axisymmetric lobes. Finally, the transient analysis of both the stall inception (SI) and the surge onset (SO) was carried out, highlighting the flow field evolution in the diffuser under these conditions.

Copyright © 2015 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

Dynamic pressure sensors distribution

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Fig. 3

Joint time–frequency graph of the test

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Fig. 4

Dimensionless head coefficient versus dimensionless flow coefficient (i.e., φ* = φ/φstall) for the tested stage with stall inception and surge limits

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Fig. 5

Power spectrum of Probe 1 at Section 20 at the beginning of the analysis window

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Fig. 6

Circumferential pressure distribution during rotating stall at Section 20 obtained with an ensemble average approach locked at fs = 0.095 f1xREV

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Fig. 7

Time-raw signal versus filtered

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Fig. 8

Differential pressure evolution in half diffuser as a function of time

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Fig. 10

Differential pressure evolution in the diffuser during a stall period

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Fig. 11

Analysis windows for SI and SO

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Fig. 12

Joint time–frequency graph of the SI analysis window

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Fig. 13

Stall pattern inception and evolution in a half diffuser for the four investigated points

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Fig. 14

Joint time–frequency graph of the SO analysis window

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Fig. 15

Differential pressure evolution in a half diffuser during approaching surge (six equivalent stall periods)

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Fig. 16

Differential pressure evolution in a half diffuser from rotating stall to surge

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Fig. 17

Joint time–frequency graph of the test at Mu = 0.85

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Fig. 18

Local pressure pattern within half diffuser at Mu = 0.85 (three equivalent stall cycles)

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Fig. 19

Differential pressure evolution in a half diffuser toward surge at Mu = 0.85

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