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SUMMARY:Jet-edge interaction tones - Dr Peter Jordan (University of Poitie
 rs)
DTSTART:20190301T130000Z
DTEND:20190301T140000Z
UID:TALK117661@talks.cam.ac.uk
CONTACT:Joseph Ibrahim
DESCRIPTION:Motivated by the problem of jet–edge interaction noise\, we 
 study the tonal dynamics that occurs when an isothermal turbulent jet graz
 es a sharp edge. We perform hydrodynamic and acoustic pressure measurement
 s to characterise the tones as a function of Mach number and streamwise ed
 ge position. The observed distribution of spectral peaks cannot be explain
 ed 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 ton
 es are due to coupling between Kelvin–Helmholtz wavepackets and a family
  of trapped\, upstream-travelling acoustic modes in the potential core\, r
 ecently studied by Towne et al. (J. Fluid Mech. vol. 825\, 2017) and Schmi
 dt 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 freque
 ncy\, whereas at low Mach number they become progressively trapped with in
 creasing frequency\, which inhibits their reflection in the nozzle plane.
LOCATION:JDB Seminar Room\, CUED
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