Research Papers: Gas Turbines: Turbomachinery

The Effect of Rotor Casing on Low-Pressure Steam Turbine and Diffuser Interactions

[+] Author and Article Information
Gursharanjit Singh

GE Power,
Rugby CV212NH, UK
e-mail: singh.gursharanjit1@gmail.com

Andrew P. S. Wheeler

Department of Engineering,
University of Cambridge,
Cambridge CB30DY, UK

Gurnam Singh

GE Power,
Rugby CV212NH, UK

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received May 9, 2016; final manuscript received July 11, 2016; published online September 20, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(2), 022607 (Sep 20, 2016) (12 pages) Paper No: GTP-16-1174; doi: 10.1115/1.4034417 History: Received May 09, 2016; Revised July 11, 2016

The present study aims to investigate the interaction between a last-stage steam turbine blade row and diffuser. This work is carried out using computational fluid dynamics (CFD) simulations of a generic last-stage low-pressure (LP) turbine and axial–radial exhaust diffuser attached to it. In order to determine the validity of the computational method, the CFD predictions are first compared with data obtained from an experimental test facility. A computational study is then performed for different design configurations of the diffuser and rotor casing shapes. The study focuses on typical flow features such as effects of rotor tip leakage flows and subsequent changes in the rotor–diffuser interactions. The results suggest that the rotor casing shape influences the rotor work extraction capability and yields significant improvements in the diffuser static pressure recovery.

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Fig. 1

Computational mesh (a) full domain, (b) rotor, (c) rotor trailing edge, and (d) tip-gap

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Fig. 2

Diffuser casing/hub profiling

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Fig. 3

(a) Test rig representative layout, (b) nonaxisymmetric diffuser (labeled as “D”), and (c) position of probes on diffuser casing [30]

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Fig. 4

Pitchwise mass-averaged absolute Mach number computed (using SA model) in the meridional plane

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Fig. 5

Rotor exit and diffuser casing flow comparisons results

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Fig. 6

Rotor and system efficiencies for testcases described in Table 1

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Fig. 7

Diffuser performance factors at SysPr = 3.92

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Fig. 8

Diffuser performance factors at SysPr = 4.40

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Fig. 9

Slice plane of static pressure contour at 97.50% span

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Fig. 10

Pitchwise average absolute Mach number (tip-gap = 1% span for C and D cases)

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Fig. 11

Local CP values computed on diffuser casing

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Fig. 12

One-dimensional performance factors along diffuser length

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Fig. 13

Rotor hade angles configurations

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Fig. 14

Diffuser performance factors for hade angle variation

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Fig. 15

Spanwise pressure and temperature distribution at rotor exit/diffuser inlet

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Fig. 16

Pitchwise absolute Mach number at different hade angles

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Fig. 17

Change in the rotor and system efficiencies with variation in hade angle

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Fig. 18

Variation in the tip leakage mass flow as a proportion of mainstream mass flow at various hade angles

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Fig. 19

Pressure difference between rotor pressure and suction surfaces indicating changes in the blade loading as hade angle is varied




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