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TECHNICAL PAPERS

Curtis Stage Nozzle/Rotor Aerodynamic Interaction and the Effect on Stage Performance

[+] Author and Article Information
Stephen Rashid

 Advanced Turbomachine, LLC, 261 N. Main Street, Wellsville, NY 14895srashid@advancedturbomachine.com

Matthew Tremmel

 ProAero Technology, 641 Nightingale Drive, Indialantic, FL 32903

John Waggott

Randall Moll

Steam Advanced Engineering, Dresser-Rand Company, 37 Coats Street, Wellsville, NY 14895

J. Turbomach 129(3), 551-562 (Jun 16, 2006) (12 pages) doi:10.1115/1.2720481 History: Received June 12, 2006; Revised June 16, 2006

Curtis, or velocity compounded, stages commonly don’t achieve the same accuracy of performance prediction expected of most other turbine stages. A review of Curtis stage design practices, field wear, and dirt patterns, in conjunction with performance testing and computational fluid dynamics (CFD) modeling, determined that the nozzle/rotor aerodynamic interaction is far more complex than typical design and performance calculations assume. Understanding this nozzle/rotor interaction is key to obtaining both improved performance, and a more accurate performance prediction. This paper discusses the nature of this interaction, and it’s implications to Curtis stage performance prediction.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Typical two row Curtis stage flowpath layout

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Figure 2

(a) test versus predicted efficiency comparison; and (b) Δη (test-predicted) versus predicted efficiency for Curtis and Rateau machines

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Figure 3

Normalized Curtis efficiency variation versus U∕C0

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Figure 4

Nozzle/rotor velocity triangle comparison between Curtis and Rateau stages

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Figure 5

Absolute/relative Mach number ratio as a function of U∕C0 and nozzle exit flow angle

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Figure 6

Rotor blades with a leading edge chamfer operating at a fixed incidence (3)

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Figure 7

Determination of unique incidence based on A∕A* or constant flow area

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Figure 8

Normalized efficiency variation versus U∕C0 for an individual turbine

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Figure 9

Nozzle exit static pressure tap locations

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Figure 10

Measured stage pressure reaction for Curtis stage testing

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Figure 11

Nozzle static pressure data versus U∕C0

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Figure 12

Overall nozzle pressure ratio versus U∕C0

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Figure 13

First rotor dirt patterns observed during a field inspection (mapped on a new blade for clarity)

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Figure 14

Radial location and extent of clean suction surface leading edge

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Figure 15

Typical areas of first rotor blade wear for long service units

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Figure 16

(a) Comparison of axial nozzle breakout area to equivalent annular height; and (b) streamtube and angle variation at the nozzle exit to maintain constant Mach number and unique rotor incidence with varying U∕C0

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Figure 17

Comparison of nozzle shape based on actual drilled-hole (left) and simulation-based adjustment (right)

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Figure 18

Actual flowpath (solid lines) versus modifications for CFD simulation (dashed lines)

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Figure 19

TCGRID-based smoothed H meshes used for TURBO (coarsened for clarity)

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Figure 20

Mesh details at interface plane

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Figure 21

Periodicity of unsteady blade surface pressure

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Figure 22

Rotor Mach contours at 50% span

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Figure 23

Rotor/nozzle wake interaction

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Figure 24

Mach contours interaction with separation region

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Figure 25

Time-averaged nozzle static pressure (left) and ideal Mach number (right)

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Figure 26

Time averaged rotor surface static pressure distributions at 15%, 50%, and 85% span

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Figure 27

Time-averaged nozzle inlet and exit flow angle and Mach number

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Figure 28

Time-averaged rotor inlet and exit flow angle and Mach number

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Figure 29

Time-averaged stage total pressure, total temperature, and efficiency distribution

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Figure 30

Time-averaged streamlines of the rotor

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