The combined dynamics of swirler and turbulent premixed swirling flames

Combining a Helmholtz solver with the flame describing function to assess combustion instability in a premixed swirled combustor

“…The local minimum, on the other hand, is seen at 60 Hz for flame A and at 98 Hz for flame B. It was shown by Palies et al (2010Palies et al ( , 2011c) that these minimum and maximum are associated to interfering acoustic and vorticity waves featuring a different propagation velocity between the plenum and the flame (perturbations in flow rate propagate at the speed of sound but also generate perturbations in the swirl number which are convected by the mean flow). When the ratio û ū b increases, the gain decreases and the two maxima slightly shift to higher or lower frequencies.…”

“…The experimental combustor designed and built at EM2C laboratory has been thorougly used to study the dynamics of turbulent swirled flames (Palies et al, 2009(Palies et al, , 2010(Palies et al, , 2011a. It comprises an upstream manifold of variable length, an axisymmetric convergent duct and a cylindrical combustion chamber of variable size schematically represented in Fig.…”

“…The interaction between combustion and acoustics is modeled by making use of a FDF determined experimentally (Palies et al, 2010). The data are expressed in terms of a gain G and a phase φ as follows:…”

“…In the work of Palies et al (2010), six different ratios of û ū b were considered as displayed in Fig. 3.…”

“…The linear behavior of the phase φ = ωτ implies that the time delay τ taken by the incident perturbation to reach the reactive region is roughly constant for all frequencies. In Palies et al (2010) it is shown that τ is associated to the mean convection velocityū b of the flow at the injector. This FDF can now be used to analyze the system dynamics with usteady combustion.…”