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Improvement of Steam Turbine Stage efficiency by Controlling Rotor Shroud Leakage Flows: Part II ? Effect of Axial Distance between a Swirl Breaker and Rotor Shroud on Efficiency Improvement

[+] Author and Article Information
Chongfei Duan

Research & Innovation Center, Mitsubishi Heavy Industries, Ltd., 1-1 Shinhama, 2-chome, Arai-cho, Takasago City, Hyogo, 676-8686, Japan
chongfei_duan@mhi.co.jp

Hisataka Fukushima

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

Kiyoshi Segawa

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

Takanori Shibata

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

Hidetoshi Fujii

Turbomachinery Headquarters, Mitsubishi Hitachi Power Systems, Ltd., 3-1, Minatomirai 3-chome, Nishi-ku, Yokohama, Kanagawa, 220-8401, Japan
hidetoshi1_fujii@mhps.com

1Corresponding author.

ASME doi:10.1115/1.4041648 History: Received August 10, 2018; Revised September 09, 2018

Abstract

The basic principle of a distinct idea to reduce an aerodynamic mixing loss induced by the difference in tangential velocity between mainstream flow and rotor shroud leakage flow is presented in "Part I -- Design Concept and Typical Performance of a Swirl Breaker". When the swirl breaker is installed in the circulating region of leakage flow at the rotor shroud exit cavity, the axial distance between the swirl breaker and rotor shroud is a crucial factor to trap the leakage flow into the swirl breaker cavity. In Part II, five cases of geometry with different axial distances between the swirl breaker and rotor shroud, which covered a range for the stage axial distance of actual high and intermediate pressure (HIP) steam turbines, were investigated using an single-rotor computational fluid dynamics (CFD) analysis and verification tests in a 1.5-stage air model turbine. By decreasing the axial distance between the swirl breaker and rotor shroud, the tangential velocity and the mixing region in the tip side which is influenced by the rotor shroud leakage flow were decreased and the stage efficiency was increased. The case of the shortest axial distance between the swirl breaker and rotor shroud increased turbine stage efficiency by 0.7% compared to the conventional cavity geometry. In addition, the measured maximum pressure fluctuation in the swirl breaker cavity was only 0.7% of the entire flow pressure. Consequently, both performance characteristics and structural reliability of swirl breaker were verified for application to real steam turbines.

Copyright (c) 2018 by ASME
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