Journal
JOURNAL OF FLUID MECHANICS
Volume 824, Issue -, Pages 202-229Publisher
CAMBRIDGE UNIV PRESS
DOI: 10.1017/jfm.2017.336
Keywords
acoustics; aeroacoustics; jet noise
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Funding
- industrial Chair ADOPSYS - Safran Aircraft Engine
- ANR [ANR-13-CHIN-0001-01]
- Labex CeLyA of the Universite de Lyon, within the programme 'Investissements d'Avenir' [ANR-10-LABX-0060/ANR-11-IDEX-0007]
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Near-field acoustic measurements and time-resolved schlieren visualisations are performed on 10 round jets with the aim of analysing the different parts of the feedback loop related to the screech phenomenon in a systematic fashion. The ideally expanded Mach number of the studied jets ranges from M-j = 1.07 to M-j = 1.50. The single source of screech acoustic waves is found at the fourth shock tip for A1 and A2 modes, and at either the third or the fourth shock tip for the B mode, depending on the Mach number. The phase of the screech cycle is measured throughout schlieren visualisations in the shear layer from the nozzle to the source. Estimates of the convective velocities are deduced for each case, and a trend for the convective velocity to grow with the axial distance is pointed out. These results are used together with source localisation deduced from a two-microphone survey to determine the number of screech periods contained in a screech loop. For the A1 and B modes, four periods are contained in a loop for cases in which the radiating shock is the fourth, and three periods when the radiating shock tip is the third, whereas the loop of the A2 mode contains five periods.
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