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SUMMARY:Combustion Dynamics of Swirling Flames
DTSTART:20120327T131500
DTEND:20120327T141500
DTSTAMP:20260916T043430Z
UID:95ed32c6e5b55571425c06995fac287e975a137e58c498f6c0785075
CATEGORIES:Conferences - Seminars
DESCRIPTION:Sébastien Candel\, Ecole Centrale Paris\, France\nInstability
  analysis of swirling flames is of importance in the design of advanced co
 mbustor concepts for aircraft propulsion and gas turbines for electricity 
 production. A few of the many issues arising in such flows are considered 
 in this seminar. It is first shown that the swirler plays an important rol
 e in the dynamics of the flow. Acoustic waves impinging on the swirler giv
 e rise to a convective vorticity mode inducing azimuthal velocity perturba
 tions and swirl number fluctuations. This mode conversion process is brief
 ly explained and illustrated by numerical simulations and validated with e
 xperimental data. It is then shown that the flame is submitted to a transm
 itted axial acoustic perturbation which propagates at the speed of sound a
 nd to an azimuthal velocity perturbation which is convected at the flow ve
 locity. The net result is that the dynamical response and unsteady heat re
 lease are determined by the combined effects of these axial and induced az
 imuthal velocity perturbations. This can then be used to determine the fla
 me transfer function. Results obtained from the model are in agreement wit
 h experiments. It is also shown that large eddy simulations of the perturb
 ed swirling flame can retrieve dynamical features observed experimentally.
  Instability analysis of a generic combustor including a swirling flame is
  then investigated by making use of a nonlinear representation of flame dy
 namics relying on the describing function. In this framework\, the flame r
 esponse is determined as a function of frequency and amplitude of perturba
 tions impinging on the combustion region. The flame describing function (F
 DF) is experimentally determined and is combined with an acoustic transfer
  matrix representation of the system to provide growth rates and oscillati
 on frequencies as a function of perturbation amplitude. These data can be 
 used to determine regions of instability\, frequency shifts with respect t
 o the acoustic eigenfrequencies and they also yield amplitude levels when 
 self-sustained oscillations of the system have reached a limit cycle. The 
 application of the FDF framework in a generic configuration indicates that
  this can be used in more general situations of technological interest.
LOCATION:ME B3 31 http://plan.epfl.ch/?lang=fr&room=me+b3+31
STATUS:CONFIRMED
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