Séminaire de Mécanique d'Orsay

Le Jeudi 6 mai 2021 à 14h00 - Webinaire - le lien sera communiqué ultérieurement

Current approaches to linear instability analysis of jets and flames

Lutz Lesshafft
LadHyX, CNRS - École Polytechnique - Institut Polytechnique de Paris

Energetic structures in jet turbulence have long been modelled as linear instability wavepackets, typically in the form of Kelvin-Helmholtz structures that develop in an axisymmetric mean flow. However, it has recently been shown, both from LES and by linear analysis, that turbulent jets also contain streaks as another dominant type of coherent structures. Streaks are generated by the lift-up mechanism, and they have been widely studied in wall-bounded flows. We have investigated how the presence of streaks in a jet baseflow modifies the characteristics of the linear Kelvin-Helmholtz instability. Flames are another class of flows that are known to sustain strong instabilities, which may involve coupled effects of hydrodynamics, acoustics and chemical reaction. We apply the formalism of global resolvent analysis to a system of equations that include all these effects, in order to characterise the physical mechanisms that lead to flame instability. First results will be presented for the optimal forcing of instabilities in a laminar conical flame, including an advanced chemical reaction model.

Accès Webinaire - le lien sera communiqué ultérieurement