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Research Papers: Gas Turbines: Turbomachinery

Direct and Indirect Noise Generated by Entropic and Compositional Inhomogeneities

[+] Author and Article Information
Erwan O. Rolland

Department of Engineering,
University of Cambridge,
Cambridge CB2 1PZ, UK
e-mail: eor21@cam.ac.uk

Francesca De Domenico, Simone Hochgreb

Department of Engineering,
University of Cambridge,
Cambridge CB2 1PZ, UK

1Corresponding author.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 16, 2017; final manuscript received September 21, 2017; published online May 4, 2018. Editor: David Wisler.

J. Eng. Gas Turbines Power 140(8), 082604 (May 04, 2018) (9 pages) Paper No: GTP-17-1458; doi: 10.1115/1.4039050 History: Received August 16, 2017; Revised September 21, 2017

Flow disturbances are generated inside a duct via pulsed injection of helium into a flow of air. This leads to the generation of an acoustic pulse (direct noise), as well as the production of entropic and compositional inhomogeneities, which are convected with the mean flow. As these inhomogeneities are convected through a choked nozzle, they generate indirect noise. The resulting acoustic pressure fluctuations are measured experimentally using pressure transducers upstream of the nozzle. Insight obtained from theoretical models and a time-delay analysis can be used to isolate and extract the contributions of direct and indirect noise in the experimental signal. These results are directly compared to existing one-dimensional (1D) direct and indirect noise models. The experimental measurement of indirect noise is found to be in good agreement with the theoretical models for entropy noise and compositional noise for a compact 1D isentropic nozzle.

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Figures

Grahic Jump Location
Fig. 1

Schematic of the direct acoustic wave, entropy wave, and compositional wave generated at the jump location, and indirect acoustic wave generated at the outlet

Grahic Jump Location
Fig. 2

Acoustic pressure resulting from a reverberated square acoustic pulse in a one-dimensional cavity

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Fig. 3

Experimental setup: flow circuit with: 1—pressure indicators, 2—valves, 3—air tank, 4—helium tank, 5—pressure regulator, 6—mass flow controller, 7—mass flow meter, and 8—fast solenoid valve

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Fig. 4

Acoustic pressure p′2 (case A2) as a function of time t for five different helium flow rates

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Fig. 5

Acoustic pressure pulse amplitude p′2 as a function of injected energy flux Φe (cases A1 and A2), compared with the theoretical 1D direct noise model

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Fig. 6

Experimental acoustic pressure p′2 (cases B1, B2, and B3) as a function of time t for a range of helium flow rates

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Fig. 7

Experimental acoustic pressure (case B1) and theoretical acoustic decay model as a function of time t for different values of R1R2 (left) and for R1R2=0.983 (right)

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Fig. 8

Reconstructed experimental direct noise (p′d) and indirect noise (p′d) (cases B1, B2, and B3)

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Fig. 9

Experimental acoustic pressure p′2 (cases C1, C2, C3) as a function of time t for a range of helium flow rates

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Fig. 10

Reconstructed experimental direct noise (p′d) and indirect noise (p′d) (cases C1, C2, and C3)

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Fig. 11

Block diagram representing the equations composing the analytical model

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Fig. 12

Experimental acoustic pressure p′2 (cases B1, B2, and B3) for a range of helium flow rates (left), analytical acoustic pressure p′ (middle), analytical acoustic pressure contributions of direct noise (p′d) and indirect noise (p′i) (right)

Grahic Jump Location
Fig. 13

Experimental acoustic pressure p′2 (cases C1, C2, and C3) for a range of helium flow rates (left), analytical acoustic pressure p′ (middle), analytical pressure contributions of direct noise (p′d) and indirect noise (p′i) (right)

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Fig. 14

Entropic (p′σ) and compositional (p′ξ) contributions to indirect noise for cases C1, C2, and C3

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Fig. 15

Comparison of experimental and theoretical peak pressures for direct noise (cases B1, B2, and B3, left) and indirect noise (cases C1, C2, and C3, right)

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