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Research Papers

Stability Enhancement by Casing Grooves: The Importance of Stall Inception Mechanism and Solidity

[+] Author and Article Information
Tim Houghton, Ivor Day

Whittle Laboratory, Cambridge University, Cambridge CB3 0DY, UK

Some cases were not tested due to a blade failure before tests were completed.

J. Turbomach 134(2), 021003 (Jun 21, 2011) (8 pages) doi:10.1115/1.4002986 History: Received July 01, 2010; Revised July 05, 2010; Published June 21, 2011; Online June 21, 2011

This paper concerns the optimization of casing grooves and the important influence of stall inception mechanism on groove performance. Installing casing grooves is a well known technique for improving the stable operating range of a compressor, but the wide-spread use of grooves is restricted by the loss of efficiency and flow capacity. In this paper, laboratory tests are used to examine the conditions under which casing treatment can be used to greatest effect. The use of a single casing groove was investigated in a recently published companion paper. The current work extends this to multiple-groove treatments and considers their performance in relation to stall inception mechanisms. Here it is shown that the stall margin gain from multiple grooves is less than the sum of the gains if the grooves were used individually. By contrast, the loss of efficiency is additive as the number of grooves increases. It is then shown that casing grooves give the greatest stall margin improvement when used in a compressor, that exhibits spike-type stall inception, while modal activity before stall can dramatically reduce the effectiveness of the grooves. This finding highlights the importance of being able to predict which stall inception mechanism might occur in a given compressor before and after grooves are added. Some published prediction techniques are therefore examined, but found wanting. Lastly, it is shown that casing grooves can, in some cases, be used to remove rotor blades and produce a more efficient, stable, and light-weight rotor.

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Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 2

Red compressor characteristics with and without casing grooves applied

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Figure 3

Layout of high-frequency response pressure transducers

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Figure 4

Graphs showing the SMI and MEI generated by a single groove as it is moved aft from the leading edge

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Figure 5

The SMI and MEI generated by multiple-groove treatments, with schematics of the groove locations

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Figure 6

Red compressor characteristics for the smooth wall and casing treatments containing one, two, and three grooves

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Figure 7

Red compressor characteristics at different IGV stagger angles with either a smooth wall or casing grooves installed

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Figure 8

High-frequency pressure measurements showing the three stall inception mechanisms observed during the IGV stagger tests

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Figure 9

The impact on casing treatment performance of changing the rotor tip incidence by restaggering the IGVs

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Figure 10

Red compressor characteristics at different rotor stagger angles with either a smooth wall or casing grooves installed

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Figure 11

Impact on casing treatment performance of changing the rotor tip incidence by restaggering the IGVs and rotor blades

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Figure 12

The axial velocity of the rotor outflow for spike and modal stalling cases (low axial velocity considered blockage)

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Figure 13

An analysis based on the model of Simpson (14) applied to cases from the IGV and rotor blade stagger experiments

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Figure 14

Red compressor characteristics showing the impact of adding a single groove with 58 and 55 blades installed

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Figure 1

The Red compressor configuration

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