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Research Papers

Experimental and Numerical Investigation of a Circumferential Groove Casing Treatment in a Low-Speed Axial Research Compressor at Different Tip Clearances

[+] Author and Article Information
Matthias Rolfes

Chair of Turbomachinery and Flight Propulsion,
Institute of Fluid Mechanics,
Technische Universität Dresden,
Dresden 01062, Germany
e-mail: Matthias.Rolfes@tu-dresden.de

Martin Lange, Konrad Vogeler, Ronald Mailach

Chair of Turbomachinery and Flight Propulsion,
Institute of Fluid Mechanics,
Technische Universität Dresden,
Dresden 01062, Germany

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 21, 2017; final manuscript received August 29, 2017; published online October 3, 2017. Editor: Kenneth Hall.

J. Turbomach 139(12), 121009 (Oct 03, 2017) (10 pages) Paper No: TURBO-17-1125; doi: 10.1115/1.4037822 History: Received August 21, 2017; Revised August 29, 2017

The demand of increasing pressure ratios for modern high pressure compressors leads to decreasing blade heights in the last stages. As tip clearances (TC) cannot be reduced to any amount and minimum values might be necessary for safety reasons, the TC ratios of the last stages can reach values notably higher than current norms. This can be intensified by a compressor running in transient operations where thermal differences can lead to further growing clearances. For decades, the detrimental effects of large clearances on an axial compressor's operating range and efficiency are known and investigated. The ability of circumferential casing grooves in the rotor casing to improve the compressor's operating range has also been in the focus of research for many years. Their simplicity and ease of installation are one reason for their continuing popularity nowadays, where advanced methods to increase the operating range of an axial compressor are known. In the authors' previous paper, three different circumferential groove casing treatments were investigated in a single-stage environment in the low-speed axial research compressor at TU Dresden. One of these grooves was able to notably improve the operating range and the efficiency of the single stage compressor at very large rotor TC (5% of chord length). In this paper, the results of tests with this particular groove type in a three stage environment in the low-speed axial research compressor are presented. Two different rotor TC sizes of 1.2% and 5% of tip chord length were investigated. At the small TC, the grooves are almost neutral. Only small reductions in total pressure ratio and efficiency compared to the solid wall can be observed. If the compressor runs with large TC, it notably benefits from the casing grooves. Both, total pressure and efficiency can be improved by the grooves in a similar extent as in single stage tests. Five-hole probe measurements and unsteady wall pressure measurements show the influence of the groove on the flow field. With the help of numerical investigations, the different behavior of the grooves at the two TC sizes will be discussed.

Copyright © 2017 by ASME
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References

Figures

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Fig. 1

LSRC Dresden—cross section of three stage build and reference parameters

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Fig. 2

Geometry of circumferential casing groove

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Fig. 3

Arrangement of pressure transducers over rotor—left: groove; right: SolidWall

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Fig. 4

Compressor speedlines for small tip clearance: (top) total pressure ratio and efficiency of the entire compressor, (bottom) static pressure ratio of second stage

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Fig. 5

Mass flow through tip gap of second rotor (solid lines) and groove (dashed line) at ξ = 1.00 for small tip clearance—CFD results

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Fig. 6

Static pressure on a plane in midgap height over second rotor at ξ = 1.00 for small tip clearance: (top) SolidWall, (bottom) groove—CFD results

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Fig. 7

Streamlines through the tip gap of second rotor near blade tip (8% of TC) at ξ = 1.00 for small tip clearance: (top) SolidWall, (bottom) groove

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Fig. 8

Compressor speed lines for large tip clearance: (top) total pressure ratio and efficiency of the entire compressor, (bottom) static pressure ratio of second stage

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Fig. 9

Pitch averaged 5HP results in MP6 downstream rotor 2 at ξ = 0.925 for large tip clearance

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Fig. 10

Static Wall pressure over second rotor at ξ = 0.925 for large tip clearance

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Fig. 11

Mass flow through rotor tip gap of second rotor and groove at ξ = 0.925 for large tip clearance—CFD results

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Fig. 12

Streamlines through the tip gap of second rotor near blade tip (8% of TC) at ξ = 0.925 for large tip clearance

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Fig. 13

Streamlines through the tip gap of second rotor near casing (83% of TC) at ξ = 0.925 for large tip clearance

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Fig. 14

Relative total pressure loss over axial chord length in second rotor at ξ = 0.925 for large tip clearance—CFD results

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Fig. 15

Streamlines through the tip gap of second rotor near casing (83% of TC) and contour of relative total pressure loss at ξ = 0.925 for large tip clearance

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