CUED Publications database

Detection of direct and indirect noise generated by synthetic hot spots in a duct

De, DF and Rolland, E and Hochgreb, S (2016) Detection of direct and indirect noise generated by synthetic hot spots in a duct. In: Thermoacoustic Instabilities in Gas Turbines and Rocket Engines: Industry meets Academia, 2016-5-30 to 2016-6-2, Munich, Germany pp. 1-14..

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Indirect noise generated by the acceleration of entropy or vorticity perturbations through a nozzle is of interest both as an additional source of transmitted noise, but also as a source of combustion instabilities via backward propagating waves. There is a lack of experimental data, mostly due to difficulties in separating direct and indirect noise. Previous experiments attempted to isolate indirect noise by generating thermoacoustic hot spots electrically and measuring the transmitted acoustic waves, yet there is no data on the reflected or backward propagating acoustic waves. In this work, synthetic hot spots are generated by unsteady electrical heating of thin wires. These hot spots are accelerated through an orifice plate, producing a strong acoustic signature upstream of the orifice plate. Using a time separation argument, we identify the indirect noise signal, showing that its contribution to the overall noise is not negligible in either in subsonic or sonic throat conditions. However, the amplitude of direct noise is larger, making indirect noise difficult to identify if the two contributions are merged. We demonstrate the importance of appropriate pressure transducer instrumentation and accounting for the respective transfer functions in order to account for low frequency effects in the determination of pressure.

Item Type: Conference or Workshop Item (UNSPECIFIED)
Uncontrolled Keywords: indirect noise entropy spots pressure transducers
Divisions: Div A > Energy
Depositing User: Cron Job
Date Deposited: 17 Jul 2017 20:03
Last Modified: 22 May 2018 06:43