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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Interaction Between the Acoustic Pressure Fluctuations and the Unsteady Flow Field Through Circular Holes

[+] Author and Article Information
Jochen Rupp1

Department of Aeronautical and Automotive Engineering, Loughborough University, Leicestershire LE11 3TU, UK

Jon Carrotte, Adrian Spencer

Department of Aeronautical and Automotive Engineering, Loughborough University, Leicestershire LE11 3TU, UK

1

On secondment from Rolls-Royce plc.

J. Eng. Gas Turbines Power 132(6), 061501 (Mar 17, 2010) (9 pages) doi:10.1115/1.4000114 History: Received March 31, 2009; Revised May 16, 2009; Published March 17, 2010; Online March 17, 2010

Gas turbine combustion systems are prone to thermo-acoustic instabilities, and this is particularly the case for new low emission lean burn type systems. The presence of such instabilities is basically a function of the unsteady heat release within the system (i.e., both magnitude and phase) and the amount of damping. This paper is concerned with this latter process and the potential damping provided by perforated liners and other circular apertures found within gas turbine combustion systems. In particular, the paper outlines experimental measurements that characterize the flow field within the near field region of circular apertures when being subjected to incident acoustic pressure fluctuations. In this way the fundamental process by which acoustic energy is converted into kinetic energy of the velocity field can be investigated. Experimental results are presented for a single orifice located in an isothermal duct at ambient test conditions. Attached to the duct are two loudspeakers that provide pressure fluctuations incident onto the orifice. Unsteady pressure measurements enable the acoustic power absorbed by the orifice to be determined. This was undertaken for a range of excitation amplitudes and mean flows through the orifice. In this way regimes where both linear and nonlinear absorption occur along with the transition between these regimes can be investigated. The key to designing efficient passive dampers is to understand the interaction between the unsteady velocity field, generated at the orifice and the acoustic pressure fluctuations. Hence experimental techniques are also presented that enable such detailed measurements of the flow field to be made using particle image velocimetry. These measurements were obtained for conditions at which linear and nonlinear absorption was observed. Furthermore, proper orthogonal decomposition was used as a novel analysis technique for investigating the unsteady coherent structures responsible for the absorption of energy from the acoustic field.

Copyright © 2010 by Rolls-Royce plc
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Figures

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Figure 1

Schematic of the experimental test rig, dimensions in millimeters not to scale

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Figure 2

Upstream and downstream traveling wave components

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Figure 3

Schematic of PIV measurement section, dimensions in millimeters not to scale

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Figure 4

Acoustic absorption without mean flow

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Figure 5

Acoustic energy loss

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Figure 6

Acoustic absorption with mean flow

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Figure 7

Transition from linear to nonlinear absorption

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Figure 8

Linear versus nonlinear absorption

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Figure 9

Rayleigh conductivity of a thin aperture (4)

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Figure 10

Schematic of aperture velocities and vena contracta

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Figure 11

Linear model comparison with experiment

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Figure 12

Nonlinear acoustic absorption dependent on the Strouhal number

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Figure 13

Cumulative energy distribution for each POD mode

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Figure 14

Example of temporal coefficients

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Figure 15

Comparison of POD modes 2 and 10

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Figure 16

Velocity spectra for POD modes 1–6

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Figure 17

Power spectral density (PSD) comparison

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Figure 18

Phase averaged reconstructed velocity field including the mean flow field (45 deg phase angle)

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Figure 19

Phase averaged reconstructed velocity field including the mean flow field (90 deg phase angle)

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Figure 20

Mean flow field comparison with and without excitation

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Figure 21

Phase averaged reconstructed velocity field including the mean flow field (45 deg phase angle)

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Figure 22

Phase averaged reconstructed velocity field including the mean flow field (180 deg phase angle)

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