Flame transfer functions and flame dynamics of premixed swirling flames*

Predicting the flame response of a premixed swirling flame poses a major challenge as it is highly dependent on the level of swirl and the geometry of the configuration. In swirling flames, characteristic troughs on the gain of the flame transfer function (FTF) can be observed at certain frequencies. While past experiments have focused on the FTF of swirling flames, a very limited number involve Computational Fluid Dynamics (CFD) and there is not sufficient understanding of the flame dynamics during the forcing cycles. In this work, we perform experiments and Large Eddy Simulations (LES) of lean premixed ethylene flames on a bluff body burner with a blockage ratio of 50%, using two swirlers with 45° and 60° vane angles. The agreement between experiments and LES is observed to be good. The level of swirl can significantly affect the flame behaviour and when the swirl number is increased the FTF trough is shifted to a higher frequency. The flame dynamics are further analysed by considering the effects of wrinkling.