Abstract
Abstract
Highlights
Combustion noise is central to efforts to curb aircraft emissions
Given that the expected gas turbine mixture fraction fluctuations are of the order of 5–10 % (Magri 2017; Giusti et al 2019), which is similar to the experimental mass fractions used in this work, both entropic and compositional fluctuations can lead to indirect noise magnitudes of the same order as direct noise
910 A5-25 entropic waves generated at a wave generator, (ii) a generalisation of the non-isentropic low-order model developed by De Domenico et al (2019a) to multi-component gases to account for composition-to-sound conversion and (iii) the relationship between the acoustic sources in a reverberating system and the resulting pressure traces
Summary
Combustion noise is central to efforts to curb aircraft emissions. Noise originating in the combustor is an important contributor to overall aircraft noise, during approach and landing phases. In the Entropy Wave Generator (EWG) developed at Deutsches Zentrum für Luft- und Raumfahrt (DLR), entropic waves were generated in a duct using an electric heater, accelerated through a subsonic or supersonic nozzle, and the resulting pressure trace was measured further downstream of the nozzle (Bake et al 2009) In those experiments, the upstream-propagating entropy noise was not measured, even though it may play a role in thermoacoustic instabilities (Polifke et al 2001; Goh & Morgans 2013). These results are compared to simulations carried out with the predictions of the proposed physics-based low-order model for non-isentropic nozzle transfer functions
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