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On the response of a rectangular supersonic jet to a near-field located parallel flat plate
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.ORCID iD: 0000-0001-7330-6965
2017 (English)In: 23rd AIAA/CEAS Aeroacoustics Conference, 2017, American Institute of Aeronautics and Astronautics, 2017Conference paper (Refereed)
Abstract [en]

In this paper, the flow and acoustic fields of a rectangular over-expanded supersonic jet interacting with a parallel plate are investigated using compressible LES. The jet exits from a converging diverging rectangular nozzle of aspect ratio 2 and of design Mach number 1.5. Four simulations with four different distances between the lower inner lip of the minor axis of the rectangular jet and the plate ranging from 0 to 3 equivalent diameters are performed. The geometry of the nozzle, the positions of the plate, and the exit conditions are chosen in order to match those in an experimental study conducted at the University of Cincinnati. Snapshots and mean velocity fields are first presented. A good agreement with the PIV experimental measurements is found. The Overall Sound Pressure Levels are then plotted along the minor and major axis. In a previous paper, the corresponding free jet has been found to undergo a strong flapping motion along the minor axis due to the screech feedback mechanism. In the present study, it is seen that the intensity of the screech feedback mechanism increases for some distances and decreases for some others compared to the one in the corresponding free jet. A study of the jets shear-layers is then proposed first by looking at two points space-time cross correlation of the axial velocity. The convection of the turbulent is thus studied. Then, two points space-time cross correlation of the pressure along the jets shear-layers are proposed and an amplification of the aeroacoustic feedback mechanism leading to screech noise is observed in the lower jet shear-layers for two cases. It is also observed that the screech feedback mechanism establishes mainly between the nozzle lips and the end of the tenth shock cell. The acoustic loading on the plate is finally studied. As pointed out in a previous study, the flapping motion of the jet at the screech frequency seems to yield to an asymmetric organization of the Mach wave radiation also at the screech frequency. Those organized Mach waves impinge in the plate and propagate back to the jet, exciting the shear-layer at the screech frequency. This will amplify the screech mechanism in the lower jet shear-layer. However, this amplification happens only for some nozzle-to-plate distances. Indeed, the screech mechanism leads to the formation of a standing wave pattern in terms of pressure loading at the screech frequency on the plate. There are regions with high amplitude, meaning the acoustic loading is organized mainly at the screech frequency, and regions with low amplitude, which means the acoustic loading is not organized mainly at the screech frequency. The amplification then depends on the location of the standing wave compared to the overall acoustic loading on the plate. If a region of high amplitude of the standing wave pattern coincide with the region of maximal acoustic loading, there is amplification of the screech mechanism.

Place, publisher, year, edition, pages
American Institute of Aeronautics and Astronautics, 2017.
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-211965Scopus ID: 2-s2.0-85023625337ISBN: 9781624105043 OAI: oai:DiVA.org:kth-211965DiVA, id: diva2:1133623
Conference
23rd AIAA/CEAS Aeroacoustics Conference, 2017, Denver, United States, 5 June 2017 through 9 June 2017
Note

QC 20170816

Available from: 2017-08-16 Created: 2017-08-16 Last updated: 2017-08-16Bibliographically approved

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