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Wednesday, July 10 • 15:50 - 16:10

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For non-isothermal jets, both the mean flow sound propagation, such as sound refraction or scattering by the jet mean flow velocity, and the effect of the jet temperature gradient on sound propagation are important. This is because in addition to the appearance of new noise sources due to enthalpy fluctuations of heated jet noise, an increase in jet temperature leads to a non-uniform distribution of the sound speed in jet flow. Neglect of the sound speed variation across the jet thermal layer leads to an error in the far-field noise levels, which error tends to increase for high-frequencies and small polar angles to the jet flow. The error increase is due to a longer time spent by the high-frequency waves in the jet and also by that of all sound waves at small polar angles in comparison with the low-frequency and 90o sound propagation, respectively. In this work, far-field noise radiated by an analytical ring source model is calculated in accordance with the Goldstein generalised acoustic analogy. The source model is representative of fluctuating Reynolds sources of various directivities from the static heated transonic SILOET jet flow at temperature ratio 2.5 as extracted from a Large Eddy Simulation. For a reference solution, we consider sound propagation in a locally parallel mean flow model with taking into account the non-uniform (also locally parallel) distribution of the sound speed in the jet. The approximate solution corresponds to the locally parallel jet flow without considering the temperature variation. The far-field noise predictions of these two models are compared for a range of the ring source locations in the shear layer, sound frequencies, and observer angles to answer the question when the neglect of the sound speed variation in a heated jet can be justified and when it can lead to a notable error in the far-field sound levels or (for solving the noise source identification problem) a misinterpretation of the noise source location in the jet.


Gwenael Gabard

Dr., LAUM, Le Mans Université


Wednesday July 10, 2019 15:50 - 16:10 EDT
Outremont 5
  T03 Aero… aircrft noise & vibr., SS02 Computational Aeroac