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Research Papers

Detached-Eddy Simulation Applied to Aeroelastic Stability Analysis in a Last-Stage Steam Turbine Blade

[+] Author and Article Information
Tianrui Sun

School of Energy and Power Engineering,
Beihang University,
Beijing 100191, China;
Department of Energy Technology,
Royal Institute of Technology,
100 44 Stockholm, Sweden
e-mail: mengzhuanjingshi@yeah.net

Paul Petrie-Repar

Department of Energy Technology,
Royal Institute of Technology,
100 44 Stockholm, Sweden
e-mail: paul.petrie-repar@energy.kth.se

Damian M. Vogt

ITSM – Institute of Thermal Turbomachinery and Machinery Laboratory,
University of Stuttgart,
Stuttgart 70569, Germany
e-mail: damian.vogt@itsm.uni-stuttgart.de

Anping Hou

School of Energy and Power Engineering,
Beihang University,
Beijing 100191, China
e-mail: houap@buaa.edu.cn

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Turbomachinery. Manuscript received October 1, 2018; final manuscript received March 30, 2019; published online May 29, 2019. Assoc. Editor: Rakesh Srivastava.

J. Turbomach 141(9), 091002 (May 29, 2019) (11 pages) Paper No: TURBO-18-1274; doi: 10.1115/1.4043407 History: Received October 01, 2018; Accepted April 02, 2019

Blade flutter in the last stage is an important design consideration for the manufacturers of steam turbines. Therefore, the accurate prediction method for blade flutter is critical. Since the majority of aerodynamic work contributing to flutter is done near the blade tip, resolving the tip leakage flow can increase the accuracy of flutter predictions. The previous research has shown that the induced vortices in the tip region can have a significant influence on the flow field near the tip. The structure of induced vortices due to the tip leakage vortex cannot be resolved by unsteady Reynolds-averaged Navier–Stokes (URANS) simulations because of the high dissipation in turbulence models. To the best of author’s knowledge, the influence of induced vortices on flutter characteristics has not been investigated. In this paper, the results of detached-eddy simulation (DES) and URANS flutter simulations of a realistic-scale last-stage steam turbine are presented, and the influence of induced vortices on the flutter stability has been investigated. Significant differences for the predicted aerodynamic work coefficient distribution on the blade surface, especially on the rear half of the blade suction side near the tip, are observed. At the least stable interblade phase angle (IBPA), the induced vortices show a destabilizing effect on the blade aeroelastic stability. The motion of induced vortices during blade oscillation is dependent on the blade amplitude, and hence, the aerodynamic damping is also dependent on the blade vibration amplitude. In conclusion, the induced vortices can influence the predicted flutter characteristics of the steam turbine test case.

Copyright © 2019 by ASME
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References

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Figures

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Fig. 1

Schematic figure of the KTH steam turbine flutter test case

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Fig. 2

Normalized wave amplitude at 0.4 chords away from the rotor for the inlet and outlet boundaries

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Fig. 3

Five numerical steam turbine models with varied outlet boundary position; the number before ac represents the average distance away from rotor exit normalized by the average axial chord. The model 5.1ac uses the same outlet position as the diffusor outlet of the Durham test case [16], and the outlet for the KTH steam turbine flutter test case.

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Fig. 4

Predicted logarithmic decrement normalized by the results of model 5.1ac for the five models

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Fig. 5

Slices of CFD mesh in the rotor domain: (a) shroud and (b) mid chord

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Fig. 6

The first flap mode shape

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Fig. 7

Tip clearance flow structure shaded by normalized helicity

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Fig. 8

Development of tip clearance vortices in the streamwise direction: the positive value of normalized helicity represents the core of induced vortices and the negative value of normalized helicity represents the core of the tip leakage vortex

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Fig. 9

Helicity contour at 98% span: the positive value of normalized helicity represents the core of induced vortices and the negative value of normalized helicity represents the core of the tip leakage vortex

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Fig. 10

Comparison of blade loading between URANS and DES cases at 98% span

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Fig. 11

Logarithmic decrement versus IBPA plot calculated by URANS and DES, together with the reference results obtained from LUFT [6]

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Fig. 12

Distribution of normalized aerodynamic damping in the spanwise direction in URANS and DES results: (a) IBPA = 0 deg, (b) IBPA = 180 deg, (c) IBPA = −45 deg

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Fig. 13

Aerodynamic work coefficient distribution at 90% and 98% span of blade by URANS and DES, IBPA = 0 deg: (a) 90% span and (b) 98% span

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Fig. 14

Aerodynamic work coefficient distribution at 90% and 98% span of blade by URANS and DES, IBPA = 180 deg: (a) 90% span and (b) 98% span

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Fig. 15

Aerodynamic work coefficient distribution at 90% and 98% span of blade by URANS and DES, IBPA = −45 deg: (a) 90% span and (b) 98% span

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Fig. 16

Tip clearance vortex structure in a blade vibration period resolved by URANS at 98% span, IBPA = −45 deg

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Fig. 17

Tip clearance vortex structure in a blade vibration period resolved by DES at 98% span, IBPA = −45 deg

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Fig. 18

Logarithmic decrement with various maximum blade vibration amplitude, IBPA = 0 deg

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Fig. 19

Aerodynamic damping distribution in spanwise with different vibration amplitudes, IBPA = 0 deg: (a) URANS and (b) DES

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Fig. 20

Aerodynamic work coefficient distribution at 90% and 98% span with various maximum blade vibration amplitudes, IBPA = 0 deg: (a) URANS and (b) DES

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Fig. 21

Tip clearance vortex structure in a blade vibration period resolved by DES with amplitude equals 0.3% chord at 98% span, IBPA = 0 deg

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Fig. 22

Tip clearance vortex structure in a blade vibration period resolved by DES with amplitude equals 3.675% chord at 98% span, IBPA = 0 deg

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