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Research Papers

Improvement of Steam Turbine Stage Efficiency by Controlling Rotor Shroud Leakage Flows—Part I: Design Concept and Typical Performance of a Swirl Breaker

[+] Author and Article Information
Takanori Shibata

Research & Innovation Center,
Mitsubishi Heavy Industries, Ltd.,
2-1-1 Shinhama, Arai-cho,
Takasago 676-8686, Hyogo, Japan
e-mail: takanori_shibata@mhi.co.jp

Hisataka Fukushima

Turbomachinery Headquarters,
Mitsubishi Hitachi Power Systems, Ltd.,
2-1-1 Shinhama, Arai-cho,
Takasago 676-8686, Hyogo, Japan
e-mail: hisataka_fukushima@mhps.com

Kiyoshi Segewa

Turbomachinery Headquarters,
Mitsubishi Hitachi Power Systems, Ltd.,
3-1-1 Saiwai-cho, Hitachi,
Ibaraki 317-8585, Japan
e-mail: kiyoshi_segawa@mhps.com

1Corresponding author.

Manuscript received August 24, 2018; final manuscript received September 10, 2018; published online November 1, 2018. Editor: Jerzy T. Sawicki.

J. Eng. Gas Turbines Power 141(4), 041003 (Nov 01, 2018) (9 pages) Paper No: GTP-18-1578; doi: 10.1115/1.4041650 History: Received August 24, 2018; Revised September 10, 2018

In high and intermediate pressure (HIP) steam turbines with shrouded blades, it is well known that shroud leakage losses contribute significantly to overall losses. Shroud leakage flow with a large tangential velocity creates a significant aerodynamic loss due to mixing with the mainstream flow. In order to reduce this mixing loss, two distinct ideas for rotor shroud exit cavity geometries were investigated using computational fluid dynamics (CFD) analyses and experimental tests. One idea was an axial fin placed from the shroud downstream casing to reduce the axial cavity gap, and the other was a swirl breaker placed in the rotor shroud exit cavity to reduce the tangential velocity of the leakage flow. In addition to the conventional cavity geometry, three types of shroud exit cavity geometries were designed, manufactured, and tested using a 1.5-stage air model turbine with medium aspect ratio blading. Test results showed that the axial fin and the swirl breaker raised turbine stage efficiency by 0.2% and 0.7%, respectively. The proposed swirl breaker was judged to be an effective way to achieve highly efficient steam turbines because it not only reduces the mixing losses but also improves the incidence angle distribution onto the downstream blade row. This study is presented in two papers. The basic design concept and typical performance of the proposed swirl breaker are presented in this part I, and the effect of axial distance between a swirl breaker and rotor shroud on efficiency improvement is discussed in part II [8].

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References

Tanuma, T. , 2017, “ Chapter I: Introduction to Steam Turbines for Power Plants,” Advances in Steam Turbines for Modern Power Plants, Elsevier, Amsterdam, The Netherlands, pp. 3–9.
Denton, J. D. , 1993, “ Loss Mechanisms in Turbomachines,” ASME J. Turbomach., 115(4), pp. 621–656. [CrossRef]
Wallis, A. M. , Denton, J. D. , and Demargne, A. J. , 2001, “ The Control of Shroud Leakage Flows to Reduce Aerodynamic Losses in a Low Aspect Ratio,” ASME J. Turbomach., 123(2), pp. 334–341. [CrossRef]
Rosic, B. , and Denton, J. D. , 2006, “ The Control of Shroud Leakage Loss by Reducing Circumferential Mixing,” ASME Paper No. GT2006-90946.
Pfau, A. , Kalfas, A. I. , and Abhari, R. S. , 2004, “ Making Use of Labyrinth Interaction Flow,” ASME Paper No. GT2004-53797.
Rosic, B. , Denton, J. D. , Curtis, E. M. , and Perterson, A. T. , 2007, “ The Influence of Shroud and Cavity Geometry on Turbine Performance—An Experimental and Computational Study—Part 2: Exit Cavity Geometry,” ASME Paper No. GT2007-27770.
Barmpalias, K. G. , Kalfas, A. I. , Abhari, R. S. , Hirano, T. , Shibukawa, N. , and Sasaki, T. , 2011, “ Design Considerations for Axial Steam Turbine Rotor Inlet Cavity Volume and Length Scale,” ASME Paper No. GT2011-45127.
Duan, C. , Fukushima, H. , Segawa, K. , Shibata, T. , and Fujii, H. , 2018, “ Improvement of Steam Turbine Stage Efficiency by Controlling Rotor Shroud Leakage Flows—Part II: Effect of Axial Distance Between a Swirl Breaker and a Rotor Shroud on Efficiency Improvement,” ASME J. Eng. Gas Turbines Power (accepted).
Segawa, K. , Shikano, Y. , Tsubouchi, K. , and Shibashita, N. , 2002, “ Development of a Highly Loaded Rotor Blade for Steam Turbines,” JSME Int. J. Ser. B Fluids Therm. Eng., 45(4), pp. 881–890. [CrossRef]

Figures

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Fig. 1

Rotor shroud seal and cavity arrangement

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Fig. 2

Schematic illustration of the rotor shroud leakage flow (stream lines were calculated from the absolute flow velocity vectors)

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Fig. 3

Schematic diagram of air turbine test facility

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Fig. 4

Tested blade geometries: (a) meridional shape (base shroud cavity case), (b) stator blade shape and (c) rotor blade shape

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Fig. 5

Tested shroud cavity geometries: (a) case 1 (base), (b) case 2 (axial fin), and (c) case 3 (swirl breaker)

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Fig. 6

Five-hole probe for traversing a rotor outlet flow

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Fig. 7

Computational domain

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Fig. 8

Computational grid for a shroud leakage flow passage

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Fig. 9

Comparison of EFD and CFD results

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Fig. 10

Calculated flow patterns within the shroud leakage flow path for case 1 (U/C0 = 0.56)

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Fig. 11

Overall stage performance for three shroud cavity cases

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Fig. 12

Measured flow distributions at the rotor outlet traversing position for cases 1 and 2 (U/C0 = 0.56): (a) stage efficiency η/ηref(%), (b) difference of efficiency (%), (c) absolute tangential velocity (m/s), and (d) absolute outlet flow angle (deg)

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Fig. 13

Calculated flow patterns within the shroud leakage flow path for case 2 (U/C0 = 0.56)

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Fig. 14

Measured flow distributions at the rotor outlet traversing position for cases 1 and 3 (U/C0 = 0.56): (a) stage efficiency η/ηref(%), (b) difference of efficiency (%), (c) absolute tangential velocity (m/s), and (d) absolute outlet flow angle (deg)

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Fig. 15

Calculated flow patterns within the shroud leakage flow path for case 3 (U/C0 = 0.56)

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Fig. 16

Comparison of EFD and CFD results of flow pattern differences between case 1 and case 3 at the rotor outlet traversing position (U/C0 = 0.56)

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Fig. 17

Measured flow distributions at the rotor outlet traversing position for cases 1 and 3 (U/C0 = 0.60): (a) stage efficiency η/ηref (%), (b) difference of efficiency (%), (c) absolute tangential velocity (m/s), and (d) absolute outlet flow angle (deg)

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