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Research Papers: Flows in Complex Systems

Experimental and Computational Study of Oscillating Turbine Cascade and Influence of Part-Span Shrouds

[+] Author and Article Information
X. Q. Huang1

 University of Durham, Durham DH1 3LE, UK

L. He2

 University of Durham, Durham DH1 3LE, UK

David L. Bell

 Alstom Power Ltd., Rugby CV21 2NH, UK

1

Present address: Northwestern Polytechnical University, China.

2

Corresponding author. Present address: Dept. of Engineering Science, Oxford University, Oxford OX1 3PJ, UK.

J. Fluids Eng 131(5), 051102 (Apr 10, 2009) (11 pages) doi:10.1115/1.3111254 History: Received September 10, 2006; Revised December 08, 2008; Published April 10, 2009

This paper presents a combined experimental and computational study of unsteady flows in a linear turbine cascade oscillating in a three-dimensional bending/flapping mode. Detailed experimental data are obtained on a seven-bladed turbine cascade rig. The middle blade is driven to oscillate and oscillating cascade data are obtained using an influence coefficient method. The numerical simulations are performed by using a 3D nonlinear time-marching Navier–Stokes flow solver. Single-passage domain computations for arbitrary interblade phase angles are achieved by using the Fourier shape correction method. Both measurements and predictions demonstrate a fully 3D behavior of the unsteady flows. The influence of the aerodynamic blockage introduced by part-span shrouds on turbine flutter has been investigated by introducing flat plate shaped shrouds at 75% span. In contrast to practical applications, in the present test configuration, the mode of vibration of the blades remains unchanged by the introduction of the part-span shroud. This allows the influence of the aerodynamic blockage introduced by the part-span shroud to be assessed in isolation from the change in mode shape. A simple shroud model has been developed in the computational solver. The computed unsteady pressures around the shrouds are in good agreement with the experimental data, demonstrating the validity of the simple shroud model. Despite of notable variations in local unsteady pressures around the shrouds, the present results show that the blade aerodynamic damping is largely unaffected by the aerodynamic blockage introduced by part-span shrouds.

Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Low-speed turbine cascade rig

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Figure 2

Pressure tappings

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Figure 3

Steady pressure distributions at six spanwise sections on three central blades. (a) Blade −1, (b) blade 0, (c) blade 1, and (d) midspan section

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Figure 4

Unsteady pressure amplitudes on five central blades

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Figure 5

Experimental test for pitchwise convergence: aerodamping contribution from five central blades (k=0.4, IBPA=0 deg)

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Figure 6

Experimental test for linearity: first harmonic pressure coefficient at 50% span section on blade 0 at two bending amplitudes (k=0.4)

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Figure 7

Experimental test for linearity: relative amplitudes of the second harmonic pressure coefficient at different spanwise sections

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Figure 8

Amplitudes of first harmonic pressure at IBPA=−60 deg: (a) suction surface and (b) pressure surface

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Figure 9

Phase angles of first harmonic pressure at IBPA=−60 deg: (a) suction surface (b) and pressure surface

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Figure 10

Global aerodynamic damping at three reduced frequencies (bold line: trend of the least stable IBPA with regard to reduced frequency)

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Figure 11

Single-passage computational domain

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Figure 12

Steady pressure distributions

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Figure 13

Amplitude and phase of unsteady pressure at k=0.4 and the least stable IBPA (σ=−60 deg): (a) 10% span section, (b) 50% span section, and (c) 95% span section

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Figure 14

Amplitude and phase of unsteady pressure at k=0.4 and the most stable IBPA (σ=120 deg): (a) 10% span section, (b) 50% span section, and (c) 95% span section

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Figure 15

Aerodamping variation along blade span (k=0.4)

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Figure 16

Overall aerodynamic damping prediction (k=0.4)

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Figure 17

Part-span shrouded linear turbine cascade (endwall on the blade tip side is removed for clarity)

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Figure 18

Mesh used for computation with part-span shrouds

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Figure 19

Effects of part-span shrouds on amplitude of the unsteady pressure response. Left: experiment. Right: calculation (k=0.4, σ=−60 deg): (a) 50% span section, (b) 70% span section, (c) 80% span section, and (d) 95% span section.

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Figure 20

Phase angle of first harmonic pressure for settings with and without part-span shrouds: (a) 50% span section, (b) 70% span section, (c) 80% span section, and (d) 95% span section

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