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Jet mixing noise model based on geometrical acoustics for the prediction of installation effects

Abstract : A jet mixing noise prediction model is developed with the objective of obtaining an accurate estimate of installation effects while maintaining a low computing time. The Tam and Auriault prediction model is used as a starting point for the source term of the new formulation. The base flow is simplified by modelling the jet as a uniform medium connected to a uniform external medium through an infinitely thin mixing layer. The propagation of sound waves from the jet to an observer located in the far field is here simulated using geometrical acoustics. The new model developed is called TAGA for Tam Auriault - Geometrical Acoustics.The TAGA model is first applied to an academic configuration, a single jet without temperature gradient placed near a flat plate. Jet noise is predicted over the entire azimuth range, at an axial plane coinciding with the nozzle outlet. With an absolute level correction, the results obtained for the microphones under the plate match the experimental data. For observer positions above the plate, the predictions are close to measurements for the frequency range corresponding to the maximum of the spectrum. The shielding effect of the plate is however overestimated for the highest frequencies. The TAGA results are then reported in a different way. The difference between the installed and isolated spectra is added to the measured isolated spectrum. This scaling method allows a more accurate spectrum shape to be obtained. A maximum deviation, between predictions and experimental data, of 1 dB for all frequencies above 1 kHz is then obtained. The study also allows to understand a secondary peak observed in the measurements. This phenomenon is indeed explained by the interference between refracted and reflected rays. A second study is conducted on a coaxial jet. The cone of silence due to refraction effects is observed at a value close to its theoretical position. Despite the differences between the jet flow and its modelling in TAGA, encouraging results are observed for a large part of the polar angle range. The scaling method is also used to predict chevrons effects. The increase in high frequency noise is well estimated by the TAGA model. The reduction at low frequency is not found by the current formulation of the model.
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Submitted on : Monday, July 13, 2020 - 11:14:11 AM
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  • HAL Id : tel-02897958, version 1

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Yann Martelet. Jet mixing noise model based on geometrical acoustics for the prediction of installation effects. Other. Université de Lyon, 2020. English. ⟨NNT : 2020LYSEC012⟩. ⟨tel-02897958⟩

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