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SUMMARY:Standing and spinning waves in axisymmetric annular combustors - G
 iulio Ghirardo\, CUED
DTSTART:20140307T130000Z
DTEND:20140307T140000Z
UID:TALK47454@talks.cam.ac.uk
CONTACT:Dr Henry Burridge
DESCRIPTION:Combustors are prone to thermoacoustic instabilities\, resulti
 ng from the coupling between acoustic modes and flame response. In the cas
 e of axisymmetric annular combustors\, the excited acoustic modes are ofte
 n of azimuthal type\, with two azimuthal modes becoming linearly unstable 
 at the same time\, sharing the same growth-rate and oscillating frequency.
  This makes the problem quite different from longitudinal instabilities\, 
 where often only one mode is unstable. Annular combustors can saturate non
 linearly to a spinning acoustic wave\, rotating in the chamber in clockwis
 e/anticlockwise direction\, or a standing wave pattern\, with fixed pressu
 re and velocity nodes at certain azimuthal positions. I’ve been investig
 ating why some combustors prefer standing to spinning or viceversa\, or ca
 n converge to both solutions. Existing literature can explain stable spinn
 ing modes. I will present 2 different mechanisms that can explain stable s
 tanding modes as well: 1) the effect of transverse forcing on the flames\,
  sweeping the flames back and forth in the azimuthal direction\; 2) the ef
 fect of a weak flame response at small amplitudes\, and strong response at
  large amplitudes.\n\nThe focus will be on unveiling the fundamental physi
 cal phenomena of the problem\, and on providing new mathematical tools to 
 study thermoacoustic problems. On the way\, you will be entertained with m
 ulti-stability\, double-hopf bifurcations (sub/supercritical)\, thermoacou
 stic triggering.\n
LOCATION:CUEd
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