Twisted absolute instability in lifted flames

Abstract : The theory of resonant modes is extended to finite length systems containing pinch points of complex axial wavenumber k0 and frequency ω0 with arbitrary ω0kk=∂2ω/∂k2. The quantity ω0kk is shown to be an important indicator of how streamwise boundary conditions modify the local absolute mode at (k0,ω0). In particular, when Im(ω0kk)>0, the pinch point is twisted, and resonant modes owing to streamwise boundary conditions may then have growth rates greater than that of the unbounded absolute mode. In this case, global instability may occur while the flow is only convectively unstable. The premixing zone between the nozzle and a lifted flame on a variable-density jet is an example of a streamwise-confined system containing a twisted pinch point. For this system, linear stability analysis is employed to locate resonant modes along a solution curve in the complex k and ω planes. The orientation of the solution curve predicts destabilization owing to streamwise confinement as well as increasing global frequency with decreasing lift-off height as observed in previous direct numerical simulations. The theory also suggests that low-frequency fluctuations observed in the simulations may be explained by beating between two resonant modes of slightly differing frequencies. © 2009 American Institute of Physics.
Type de document :
Article dans une revue
Physics of Fluids, American Institute of Physics, 2009, 21 (1), pp.015110. 〈10.1063/1.3068758〉
Liste complète des métadonnées

Littérature citée [23 références]  Voir  Masquer  Télécharger
Contributeur : Denis Roura <>
Soumis le : lundi 7 juillet 2014 - 18:19:06
Dernière modification le : jeudi 10 mai 2018 - 02:03:38
Document(s) archivé(s) le : mardi 7 octobre 2014 - 10:45:57


Fichiers éditeurs autorisés sur une archive ouverte




Joseph Nichols, Jean-Marc Chomaz, Peter Schmid. Twisted absolute instability in lifted flames. Physics of Fluids, American Institute of Physics, 2009, 21 (1), pp.015110. 〈10.1063/1.3068758〉. 〈hal-01002605〉



Consultations de la notice


Téléchargements de fichiers