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Research Papers

Casing Treatment for Desensitization of Compressor Performance and Stability to Tip Clearance

[+] Author and Article Information
Mert Cevik

Department of Mechanical Engineering,
École Polytechnique de Montréal,
2900 boulevard Edouard-Montpetit,
2500 chemin de Polytechnique,
Montreal, QC H3T 1J4, Canada
e-mail: mert.cevik@polymtl.c

Huu Duc Vo

Mem. ASME
Department of Mechanical Engineering,
École Polytechnique de Montréal,
2900 boulevard Edouard-Montpetit,
2500 chemin de Polytechnique,
Montreal, QC H3T 1J4, Canada
e-mail: huu-duc.vo@polymtl.ca

Hong Yu

Pratt and Whitney Canadal,
1801 Courtneypark Drive East,
Mississauga, ON L5T 1J3, Canada
e-mail: hong.yu@pwc.ca

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 1, 2015; final manuscript received April 12, 2016; published online June 22, 2016. Assoc. Editor: John Clark.

J. Turbomach 138(12), 121008 (Jun 22, 2016) (16 pages) Paper No: TURBO-15-1242; doi: 10.1115/1.4033420 History: Received November 01, 2015; Revised April 12, 2016

This paper presents the development of a novel casing treatment to reduce compressor performance and stall margin sensitivities to tip clearance increase. A linked research project on blade design strategies for desensitization had discovered two flow features that reduce sensitivity to tip clearance, namely increased incoming meridional momentum in the rotor tip region and reduction/elimination of double tip leakage flow. Double tip leakage flow is the flow that exits one tip clearance and enters the tip clearance of the circumferentially adjacent blade instead of convecting downstream out of the blade passage. A new and practical casing treatment was developed and analyzed through Reynolds-averaged Navier–Stokes (RANS) computational fluid dynamics (CFD) simulations to decrease double tip leakage and reduce or even eliminate performance and stall margin sensitivity to tip clearance size. The casing treatment design consists of sawtooth-shaped circumferential indentations placed on the shroud over the rotor with a depth on the order of the tip clearance size. A detailed analysis of the flow field allowed for the elucidation of the flow mechanism associated with this casing treatment. A computational parametric study gave preliminary design rules for minimizing both performance/stall margin sensitivity to tip clearance and nominal performance loss. An improved casing indentation design was produced for which CFD simulations showed a complete desensitization of pressure ratio and stall margin while reducing efficiency sensitivity significantly for the tip clearance range studied with only a very small penalty in nominal pressure ratio. Further simulations showed that this casing treatment can be combined with desensitizing blade design strategies to further reduce tip sensitivity and reduce/eliminate/reverse nominal performance penalty. Lastly, preliminary CFD simulations on an axial compressor stage indicate that this shallow indentations' casing treatment strategy remains effective in a stage environment.

Copyright © 2016 by ASME
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References

Figures

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Fig. 1

Velocity components of regular tip leakage flow (black) versus double tip leakage flow (red) at a particular blade chord position [19]

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Fig. 2

3D view (top) and cross-sectional view schematic (bottom) of proposed nominal casing treatment design for tip desensitization

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Fig. 3

Proposed mechanism for tip desensitization by circumferential shallow indentations casing treatment

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Fig. 4

Radial and meridional view of computational domain with boundary conditions

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Fig. 5

Rotor mesh at blade tip [19]

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Fig. 6

Casing indentation shape and mesh

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Fig. 7

Definition of interface position for stall margin [19]

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Fig. 8

Tip leakage flow streamlines released from the suction surface side of the tip gap of BASE rotor at maximum t.c. size in relative frame for smooth and nominal negative sawtooth indentations casings

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Fig. 9

Variation of double tip leakage proportion with tip clearance size for BASE rotor with smooth casing versus nominal negative sawtooth casing indentations

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Fig. 10

Spanwise distribution of (a) blade loading and (b) inlet meridional momentum for BASE rotor at nominal t.c. size with smooth casing versus nominal negative sawtooth casing indentations

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Fig. 11

Sensitivity analysis results for BASE rotor with smooth casing versus nominal negative sawtooth casing indentations

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Fig. 12

Static entropy distribution at tip clearance entrance for small (0.47% tip chord) and maximum (1.41% tip chord) for BASE rotor with smooth casing versus with nominal negative sawtooth casing indentations

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Fig. 13

BASE rotor radial velocity contours at shroud plane for nominal negative sawtooth casing indentations at nominal tip clearance seen in (a) top view and (b) at the outer span of the 0.62cx axial plane

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Fig. 14

Contours of turbulence kinetic energy (TKE) (left) and entropy (right) for outer 20% span at 0.62cx axial plane for smooth casing versus nominal negative sawtooth casing indentations at nominal tip clearance

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Fig. 15

Variation of the injected mass flow rate from nominal negative sawtooth indentation grooves with tip clearance size

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Fig. 16

Chordwise distribution of nondimensional streamwise (top) and normal components (bottom) of t.c. flow velocity at tip gap exit, mass-averaged over the t.c. height for the smooth casing and with nominal negative sawtooth casings (at nominal t.c.)

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Fig. 17

Comparison of the four flow parameters for BASE rotor with smooth casing versus with nominal negative sawtooth casing indentations at minimum tip clearance

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Fig. 18

Final casing treatment design for BASE rotor

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Fig. 19

Sensitivity analysis results for BASE rotor with smooth casing, nominal and final casing indentation designs

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Fig. 20

Flow parameters comparison at nominal t.c. size for final versus nominal casing indentation

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Fig. 21

Final casing indentation design on the FFCS rotor

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Fig. 22

Sensitivity analysis of the BASE and FFCS rotors without and with final casing indentation design

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Fig. 23

Sensitivity analysis for the axial compressor stage with smooth casing versus with final casing indentation design over the rotor

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Fig. 24

Change of performance with tip clearance size for the BASE rotor at design corrected mass flow with smooth casing versus with nominal casing indentation using steady and unsteady simulations

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Fig. 25

Radial velocity contours at shroud plane for nominal casing indentation at nominal tip clearance for steady and unsteady simulations

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Fig. 26

Change of total pressure ratio for the BASE rotor versus number of spanwise (left) and streamwise (axial) (right) number of nodes per casing indentation

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