Grégoire Varillon, Thomas Ludwig Kaiser, Philipp Brokof, Dominik Weißbach, Kilian Oberleithner, et al.. Couplings in a non-uniform compressible swirling jet with a modelled swirler. Journal of Fluid Mechanics, 2026, pp.A61. ⟨10.1017/jfm.2026.11497⟩. ⟨hal-05674153⟩ Plus de détails...
We give evidence of non-modal amplification mechanisms driven by swirl intensity from a bi-global linear analysis of a cold swirling flow representative of a premixed swirl burner: non-uniform, compressible, turbulent, enclosed and subject to vortex breakdown passed the expansion. The monolithic computational approach embeds a realistic axisymmetric swirler model in the computational domain. The amplification mechanisms are identified by stability and resolvent analysis under variations of the length of the annular duct section and combustion chamber, the swirl intensity and the swirler position. While the spectrum is affected by changes in the length only, the gain of the resolvent strongly depends on the swirl intensity. The results suggest an acoustically dominated amplification in the combustion chamber and a non-modal hydrodynamic-dominated process driven by the swirl intensity. Inertial waves carrying swirl fluctuations play a key role in the latter. The results are complemented by a resolvent sensitivity analysis that identifies the tip of the inner recirculation region and the surrounding shear layer as a wavemaker region that drives at high swirl numbers the non-modal amplification. The sensitivity of that region also enables the transfer of azimuthal momentum perturbations to axial momentum, hence activating a longitudinal acoustic resonance from azimuthal fluctuations.
Grégoire Varillon, Thomas Ludwig Kaiser, Philipp Brokof, Dominik Weißbach, Kilian Oberleithner, et al.. Couplings in a non-uniform compressible swirling jet with a modelled swirler. Journal of Fluid Mechanics, 2026, pp.A61. ⟨10.1017/jfm.2026.11497⟩. ⟨hal-05674153⟩
Grégoire Varillon, Wolfgang Polifke. Amplification of perturbations in a laminar premixed swirl flame with the resolvent analysis. International Journal of Spray and Combustion Dynamics , 2026, 18 (2), pp.133-144. ⟨10.1177/17568277261449897⟩. ⟨hal-05674680⟩ Plus de détails...
The global linear stability of a swirl-stabilized laminar flame is analyzed with a monolithic approach based on linearized reactive flow equations. The computational set-up is axisymmetric with an embedded and spatially resolved swirler model to circumvent the use of ad-hoc swirl profile and fluctuation at the inlet. An input–output analysis reveals that the azimuthal and axial components of inertial waves dominate the contribution of inertial waves in gain modulation at low and high frequencies, respectively. A resolvent analysis then identifies the optimal amplification mechanism, which is found to correspond to the flame angle oscillation mechanism observed in experiments. The large gain separation explains why this optimal mechanism also appears in experiments or simulations with acoustic forcing at the inlet. Finally, flame displacement is correlated with radial velocity fluctuations at the base of the flame, which are quasi-normal to the flame sheet. This component of the fluctuating velocity is amplified along the flame sheet until it reaches its tip only if flame-flow feedback is active.
Grégoire Varillon, Wolfgang Polifke. Amplification of perturbations in a laminar premixed swirl flame with the resolvent analysis. International Journal of Spray and Combustion Dynamics , 2026, 18 (2), pp.133-144. ⟨10.1177/17568277261449897⟩. ⟨hal-05674680⟩
Journal: International Journal of Spray and Combustion Dynamics
