Measurements of the effect of boundary conditions on upstream and downstream noise arising from entropy spots
Proceedings of the ASME Turbo Expo
The American Society of Mechanical Engineers
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De, D. F., Rolland, E., & 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-2017 https://doi.org/10.1115/GT2017-64378
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 semi-infinite tube that acts as an anechoic termination for a limited time-window. The experiments show 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, the experiments show that the assumption of an isentropic nozzle of Marble and Candel  does not hold, but that an alternative theory which takes into account the partial acoustic energy dissipation through an orifice  offers good agreement with the experiments. Finally, we show 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.
Francesca De Domenico is supported by the Honorary Vice-Chancellor’s Award and a Qualcomm/DTA Studentship (University of Cambridge). Erwan Rolland is supported by an EPSRC DTA studentship (University of Cambridge). Experiments were partly funded by EPSRC grant EP/K02924X/1.
External DOI: https://doi.org/10.1115/GT2017-64378
This record's URL: https://www.repository.cam.ac.uk/handle/1810/264957