Skip to Main content Skip to Navigation
Theses

Développement d'une méthode de mesure de la masse volumique par diffusion Rayleigh appliquée à l'étude du bruit de jets, et contribution à l'étude du screech dans les jets supersoniques sous détendus

Abstract : In this research study, developments of optical diagnosis techniques are presented, and are put into practice in an aeroacoustics study of high speed and high Reynolds jets. The results described here are obtained from Schlieren visualization, and in the majority from density measurements through Rayleigh scattering. These measurement methods are applied for subsonic and supersonic jets, and associated with far field acoustics measurements. Rayleigh scattering measurements rely on laser light scattered by the molecules constituting the flow, thus they are non-intrusive. However, some difficulties in interpreting the results arise when the flow contains dust particles. This problem is partly solved by using air filters in the wind tunnel, but some residual dust particles remain, thus a software based signal cleaning method has been developed and is applied to the signals during post-processing. Besides, the signals obtained from Rayleigh scattering are very weak, and dominated by a shot noise. The noise level has been significantly reduced following the optimization of the chain of acquisition in comparison with actual apparatus. Moreover, a method to compute spectra despite the shot noise level has been adapted from a classic method to be usable with a single sensor instead of two. The analysis of radial profiles of density measured with the Rayleigh scattering apparatus shows that a similarity law allows to superimpose radial profiles measured in jets exhausted from three different nozzles at Mach 0.9 and Mach 0.7. Another similarity law is observed for radial profiles of 0 rms when they are measured far enough form the nozzle. The analysis of density spectra in the mixing layer points out the presence of a local maximum of central frequency found between St = 0:2 and St = 2 depending on the probed location, which is not as clearly observed in velocity spectra. The spatial evolution of this maximum is found different whether the flow is initially laminar or turbulent at the nozzle exit. The dependence of spectra to the Mach number, and to the difference of density between the jet and the surrounding is also studied. A scaling law is empirically determined for the scope of the study. Simultaneous measurements of density and farfield acoustic acquired in a Mach 0.9, and a supersonic ideally expanded Mach 1.32 jets are processed to obtain coherence, and conditional averaging. The results emphasis the role of large structures downstream the end of the potential core in acoustic radiations. Finally, the screech in underexpended jets is studied. This work results in the identification of the acoustic feedback source location for A1, A2 and B modes, and in the characterization of the changes in the loop structure associated with mode switching.
Keywords : Shot noise
Document type :
Theses
Complete list of metadatas

Cited literature [152 references]  Display  Hide  Download

https://tel.archives-ouvertes.fr/tel-02611970
Contributor : Abes Star :  Contact
Submitted on : Monday, May 18, 2020 - 6:15:16 PM
Last modification on : Wednesday, July 8, 2020 - 12:42:09 PM

File

TH_2607_bmercier_versiondéfin...
Version validated by the jury (STAR)

Identifiers

  • HAL Id : tel-02611970, version 1

Citation

Bertrand Mercier. Développement d'une méthode de mesure de la masse volumique par diffusion Rayleigh appliquée à l'étude du bruit de jets, et contribution à l'étude du screech dans les jets supersoniques sous détendus. Autre. Université de Lyon, 2017. Français. ⟨NNT : 2017LYSEC061⟩. ⟨tel-02611970⟩

Share

Metrics

Record views

59

Files downloads

156