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Measurements of the effect of boundary conditions on upstream and downstream noise arising from entropy spots

De Domenico, F and Rolland, EO and Hochgreb, S (2017) Measurements of the effect of boundary conditions on upstream and downstream noise arising from entropy spots. Proceedings of the ASME Turbo Expo, 2C-201.

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Abstract

Copyright © 2017 ASME. Pressure fluctuations in combustors arise either directly from the heat release rate perturbations of the flame (direct noise), or indirectly from the acceleration of entropy, vorticity or compositional perturbations through nozzles or turbine guide vanes (indirect noise). In this work, the generation of synthetic entropy spots via the Joule effect produces direct noise, and their acceleration through orifice plates and nozzles produces indirect noise. These acoustic waves reverberate, reflecting several times at the boundaries to add up to the measured pressure. Single travelling pulses are isolated by the introduction of a semiinfinite tube that acts as an anechoic termination for a limited time-window. It is shown how the shape of the converging nozzle does not affect the reflection of the direct noise wave, confirming the hypothesis of a compact nozzle. Further, it is demonstrated that the assumption of an isentropic nozzle does not hold, but that an alternative theory which takes into account the partial acoustic energy dissipation offers good agreement with the experiments. Finally, it is shown that the reflected indirect noise is underpredicted by isentropic theories. An extension of the present work is indicated for the measurement of the transmissivity of indirect noise.

Item Type: Article
Subjects: UNSPECIFIED
Divisions: Div A > Energy
Depositing User: Cron Job
Date Deposited: 17 Jul 2017 19:54
Last Modified: 21 Nov 2017 03:08
DOI: