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Communication Dans Un Congrès Année : 2023

Tone generation in impinging jets with laminar and highly-disturbed nozzle-exit boundary layers

Résumé

The tone generation in jets with laminar and highly-disturbed nozzle-exit boundary layers impinging on a plate is investigated. Seven initially laminar jets and seven jets with a nozzle-exit turbulent intensity of 9% are considered. The jets all impinge on a plate located at a distance of 8 nozzle radii from the nozzle and have Mach numbers M ranging from 0.6 to 1.3. For M ≤ 0.8 for the laminar jets and for M = 0.6 for the highly-disturbed jets, the sound radiation is broadband. For higher Mach numbers, tones emerge by more than 10 dB in the near-nozzle pressure spectra for both exit boundary-layer states. The tones are produced by feedback loops establishing between the nozzle and the plate, involving downstream-travelling Kelvin-Helmholtz instability waves and upstream-travelling guided jet waves. The tone frequencies do not depend on the state of the boundary layer. They are organized into stages as the Mach number increases and they fall in the frequency bands of the guided jet waves closing the feedback loop. Moreover, for both initially laminar and highly-disturbed jets, the dominant tone is related to an axisymmetric oscillation mode, except for M = 1.1. In the latter case, tones of similar amplitudes are linked to the axisymmetric and the first helical modes. Therefore, the azimuthal structure of the jet is not significantly affected by the nozzle-exit turbulent intensity. This is not the case for the levels and prominence of the tones, which are lower for the initially laminar jets than for the other ones, suggesting a weaker resonance in the former case. This weaker resonance appears to be due to a lower amplification of the shear-layer instability waves between the nozzle and the plate at the tone frequencies.
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Dates et versions

hal-04122925 , version 1 (08-06-2023)

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Mathieu Varé, Christophe Bogey. Tone generation in impinging jets with laminar and highly-disturbed nozzle-exit boundary layers. 29th AIAA/CEAS Aeroacoustics Conference, Jun 2023, San Diego, United States. pp.3745, ⟨10.2514/6.2023-3745⟩. ⟨hal-04122925⟩
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