The understanding of the formation of self excited pressure oscillations in technical combustion systems depends on the knowledge of the dynamical behaviour of the flame used. As an important mechanism driving these combustion instabilities the formation and reaction of coherent large-scale ring-vortices has been indentified. The phenomenon is investigated with numerical simulations using “Unsteady Reynolds-Averaged Navier-Stokes” (URANS)-methods, applying the k-ε turbulence model and a “Turbulent-Flamespeed-Closure” (TFC) combustion model. Firstly, a premixed turbulent axial methane jet flame with a thermal load of 40 kW was calculated using steady-state flow conditions. The axial distibutions of the measured radiation of OH-radicals and the calculated reaction rate show good agreement, if the turbulent burning velocity is reduced versus the original formulation. The axial positions of the maxima of the curves coincide and are applied to define a characteristic overall time delay. Secondly, a pulsed flame with a forcing frequency of 100 Hz was calculated. An additional transport equation for the residence time of fuel was solved. The analysis of the distribution of the residence time showed, that the characteristic overall time delay of the steady-state flame is a good approximation for the overall time delay of the pulsed flame. Thirdly, the flame frequency response of the pulsed flame was calculated up to frequencies of 200 Hz. For the calculation with reduced burning velocity the phase angle function of the flame coincides with the measurement and shows the typical behaviour of an ideal idle-time model.

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