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Research Papers: Gas Turbines: Turbomachinery

Three-Dimensional Blade Stacking Strategies and Understanding of Flow Physics in Low-Pressure Steam Turbines—Part II: Stacking Equivalence and Differentiators

[+] Author and Article Information
Said Havakechian

Alstom,
Baden 5401, Switzerland
e-mail: said.havakechian@power.alstom.com

John Denton

Emeritus Professor
Whittle Laboratory,
Department of Engineering,
University of Cambridge,
North Yorkshire DL84LG, UK
e-mail: jdd1@cam.ac.uk

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 20, 2015; final manuscript received September 10, 2015; published online November 17, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(6), 062601 (Nov 17, 2015) (13 pages) Paper No: GTP-15-1352; doi: 10.1115/1.4031642 History: Received July 20, 2015; Revised September 10, 2015

Optimization of blade stacking in low-pressure (LP) steam turbine development constitutes one of the most delicate and time-consuming parts of the design process. This is the second part of two papers focusing on stacking strategies applied to the last stage guide vane and represents an attempt to discern the aerodynamic targets that can be achieved by each of the well-known and most often used basic stacking schemes. The effects of lean and twist have been investigated through an iterative process, involving comprehensive 3D computational fluid dynamics (CFD) modeling of the last two stages of a standard LP, where the basic lean and twist stacking schemes were applied on the last stage guide vanes while keeping the throat area (TA) unchanged. It has been found that it is possible to achieve the same target value and pattern of stage reaction by applying either tangential lean or an equivalent value of twist. Moreover, the significance of axial sweep on hub reaction has been found to become pronounced when the blade sweep is carried out at constant TA. The importance of hub-profiling has also been demonstrated and assessed. Detailed analysis of the flow fields has provided an overall picture, revealing the differences in the main flow parameters as produced by each of the alternative basic stacking schemes.

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References

Figures

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Fig. 4

Impacts of uniform G0 restaggering on static pressure distribution at the trailing and LEs of G0

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Fig. 5

Illustration of the applied change in gauge angle for the hub only and tip only twist stacking at constant TA

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Fig. 8

Impact of hub stacking on the radial distributions of stage degree of reaction—comparison of hub only twists and the corresponding equivalent hub only lean

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Fig. 9

Comparison of impact of hub only twist/lean on spanwise variation of Mach number at G0 TE

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Fig. 6

Illustration of the applied hub only and tip only lean stacking (black: PS convexing and gray: SS convexing)

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Fig. 7

Illustration of the applied full-span lean stacking and their equivalent full-span twist (G0 gauge angle change) stacking

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Fig. 10

Impact of not keeping the G0 TA constant on the G0 inlet flow angle

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Fig. 11

Impact of tip stacking on the radial distributions of stage degree of reaction—comparison of tip only twists and the corresponding equivalent tip only lean

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Fig. 12

Comparison of impact of tip only twist/lean on spanwise variation of Mach number at G0 TE

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Fig. 14

Comparison of impact of full-span twist/lean on spanwise variation of Mach number at G0 TE

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Fig. 15

Illustration of the applied sweep change on G0: thin black—datum and beaded line—pronounced forward sweep (orthogonal stacking at the casing)

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Fig. 13

Impact of full-span stacking on the radial distributions of stage degree of reaction—comparison of full-span twists and the corresponding equivalent full-span lean

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Fig. 3

Impacts of uniform G0 restaggering on L0 radial distribution of stage reaction

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Fig. 20

Impacts of G0 hub-profiling on the radial distributions of L0 stage reaction

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Fig. 2

Example of advanced 3D G0 design

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Fig. 21

Comparisons of spanwise variations of meridional pitch angle at G0 TE (hub lean only stacking versus hub twist only stacking)

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Fig. 22

Comparisons of spanwise variations of meridional pitch angle at L0 TE (hub lean only stacking versus hub twist only stacking)

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Fig. 1

Meridional view of the standard LP last two stages employed for the 3D numerical investigations

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Fig. 16

Impacts of the applied sweep change datum to orthogonal sweep (tram lines) and orthogonal sweep at constant TA on G0 (dashed line)—illustration of spanwise distributions of L0 stage reaction

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Fig. 17

Spanwise variation of exit Mach number at the G0 TE—impacts of the applied sweep change at constant TA on G0

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Fig. 19

Illustrations of stream surface twist and streamline pattern in the casing zone for (a) datum G0 and (b) orthogonal swept G0

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Fig. 23

Comparisons of spanwise variations of mass flow density at G0 TE (hub lean only stacking versus hub twist only stacking)

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Fig. 24

Impact of various stacking schemes on percentage change in averaged leaving energy at the L0 TE for the five considered stacking schemes

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Fig. 25

Impact of various stacking schemes on tangentially averaged relative inlet Mach number to L0 at 10% blade height for the five considered stacking schemes

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Fig. 26

Impact of various stacking schemes on tangentially averaged relative inlet Mach number to L0 at 90% blade height for the five considered stacking schemes

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Fig. 18

Comparisons of spanwise variations of mass flow density at G0 TE (datum, orthogonal sweep, and tip only twist)

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