Research Papers

The Impact of Inlet Distortion and Reduced Frequency on the Performance of Centrifugal Compressors

[+] Author and Article Information
A. Grimaldi

Baker Hughes, a GE company (BHGE),
Florence 50127, Italy
e-mail: angelo.grimaldi@bhge.com

V. Michelassi

Baker Hughes, a GE company (BHGE),
Florence 50127, Italy
e-mail: vittorio.michelassi@bhge.com

Manuscript received June 29, 2018; final manuscript received July 9, 2018; published online October 1, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(2), 021012 (Oct 01, 2018) (9 pages) Paper No: GTP-18-1401; doi: 10.1115/1.4040907 History: Received June 29, 2018; Revised July 09, 2018

This paper discusses the impact of inlet flow distortions on centrifugal compressors based upon a large experimental data base in which the performance of several impellers in a range of corrected flows and corrected speeds have been measured after been coupled with different inlet plenums technologies. The analysis extends to centrifugal compressor inlets including a side stream, typical of liquefied natural gas applications. The detailed measurements allow a thorough characterization of the flow field and associated performance. The results suggest that distortions can alter the head by as much as 3% and efficiency of around 1%. A theoretical analysis allowed to identify the design features that are responsible for this deviation. In particular, an extension of the so-called “reduced-frequency,” a coefficient routinely used in axial compressors and turbine aerodynamics to weigh the unsteadiness generated by upstream to downstream blade rows, allowed to determine a plenum-to-impeller reduced frequency that correlates very well with the measured performance. The theory behind the new coefficient is discussed together with the measurement details and validates the correlation that can be used in the design phase to determine the best compromise between the inlet plenum complexity and impact on the first stage.

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Fig. 1

First stage configuration (a), intermediate stage configuration (b), intermediate stage with side stream configuration (c)

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Fig. 2

Flow distortions in terms of inlet absolute flow angle associated with different plenum types

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Fig. 3

Impeller inlet vector diagram; C+ is the absolute velocity in the left half of the plenum, C refers to the right half

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Fig. 4

Typical deviations of polytrophic efficiency (left), and work coefficient (right), solid line = intermediate stage, dashed line = first stage

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Fig. 6

Sketch of the impeller parameters

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Fig. 7

Deviation from expected work coefficient as a function of reduced frequency, Fred. Different symbols refer to different configurations listed in Table 3.

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Fig. 8

Yaw angle (above) and relative angle (below) as seen by the impeller at the plenum exit section, 90% span along the circumference: (a) no IGV, (b) straight IGV, and (c) cambered IGV. (y-axis scale in common for the three plots).

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Fig. 9

FFT of the yaw angle at the plenum exit along the circumference at 90% span: (a) no IGV, (b) straight IGV, and (c) cambered IGV

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Fig. 10

Incidence at impeller tip

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Fig. 11

Computed versus measured work coefficient as a function of the inlet contribution only

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Fig. 12

Meridional section in the proximity to the impeller leading edge. Solid line = first stage with inlet plenum, dot-dash line = intermediate stage.

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Fig. 13

Relative Mach number at blade tip. Solid line = low curvature inlet with 16 IGV, dashed line = intermediate stage with high curvature.

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Fig. 14

Relative Mach number and Incidence at blade tip. Same meridional curvature and different number of upstream vanes.

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Fig. 15

Deviation from expected polytrophic efficiency as a function of reduced frequency, Fred

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Fig. 16

Expected impact on stage performance



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