Jet–flap interaction tones. (23rd August 2018)

• Record Type: Journal Article
• Authors: Jordan, Peter; Jaunet, Vincent; Towne, Aaron; Cavalieri, André V. G.; Colonius, Tim; Schmidt, Oliver; Agarwal, Anurag
• Is Part Of: Journal of fluid mechanics. Volume 853(2018)
• Page Start: 333
• Page End: 358
• Publication Date: 2018-08-23
• Subjects: aeroacoustics, -- instability, -- jet noise; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2018.566
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract : Motivated by the problem of jet–flap interaction noise, we study the tonal dynamics that occurs when an isothermal turbulent jet grazes a sharp edge. We perform hydrodynamic and acoustic pressure measurements to characterise the tones as a function of Mach number and streamwise edge position. The observed distribution of spectral peaks cannot be explained using the usual edge-tone model, in which resonance is underpinned by coupling between downstream-travelling Kelvin–Helmholtz wavepackets and upstream-travelling sound waves. We show, rather, that the strongest tones are due to coupling between Kelvin–Helmholtz wavepackets and a family of trapped, upstream-travelling acoustic modes in the potential core, recently studied by Towne et al. ( J. Fluid Mech. vol. 825, 2017) and Schmidt et al. ( J. Fluid Mech. vol. 825, 2017). We also study the band-limited nature of the resonance, showing the high-frequency cutoff to be due to the frequency dependence of the upstream-travelling waves. Specifically, at high Mach number, these modes become evanescent above a certain frequency, whereas at low Mach number they become progressively trapped with increasing frequency, which inhibits their reflection in the nozzle plane.