• Hydrogen
• instabilities
• regimes
• thermoacoustic
• thermodiffusive

This study investigates the dynamic response of laminar premixed lean hydrogen flames under combined thermoacoustic and thermodiffusive instabilities, using two-dimensional Direct Numerical Simulations with sinusoidal inlet velocity perturbations. A range of excitation amplitudes and frequencies is explored, and the flame response is characterized through the Flame Describing Function (FDF). Three response regimes are identified: (i) low amplitudes where the flame is largely unaffected, (ii) intermediate amplitudes where thermodiffusive instabilities induce flame wrinkling and multiple frequency components, and (iii) high amplitudes where imposed oscillations dominate the flame dynamics. A comparison between the time evolution of the integrated fuel reaction rate and that of the flame surface area reveals weak correlation in the first two regimes and strong correlation in the third. The study also highlights the dependence of instability dominance on forcing frequency and amplitude.