Influence of flame-to-flame interactions on statistical characteristics of premixed turbulent combustion

Journal article, 2026

This work aims to explore the influence of local flame-to-flame interactions on various statistical characteristics of premixed turbulent flames. For this purpose, a Direct Numerical Simulation (DNS) database obtained from 17 complex-chemistry lean hydrogen-air flames propagating in forced turbulence in a box is screened and a single case characterized by the largest magnitude of oscillations in turbulent burning velocity 𝑈_𝑇 with time 𝑡 is chosen for further analysis. This newly computed case is characterized by the equivalence ratio 𝜙 = 0.5, a high Karlovitz number, with Kolmogorov length scale being smaller than reaction zone thickness in the counterpart unperturbed laminar flame by an order of magnitude. Five different instants 𝑡𝑛 are selected around the highest peak of 𝑈_𝑇 (𝑡). Results obtained by analyzing these five snapshots show a rapid decrease in flame surface area and burning velocity from 𝑡₃ to 𝑡₅ due to local flame collisions, which mostly occur due to implosion of negatively curved flames (tunnel closure), with such events being mainly localized to the trailing zone of the mean flame brush. In addition to that decrease in the flame surface area and burning velocity, such flame
collisions (i) can result (with a low probability) in appearance of local flame zones characterized by highly negative curvature and very large displacement speed and (ii) significantly affect statistics of flame curvature and tangential-diffusion contribution 𝑆_𝑑,𝑡 to displacement speed 𝑆_𝑑 . On the contrary, the influence of flame collisions on the statistics of 𝑆_𝑑 , heat release and fuel consumption rates, temperature, and mass fractions of various species is minor (if any). While flame collisions can mimic appearance of thickened reaction zones when two reaction zones merge, the statistics of the absolute value |∇𝑐_𝐹| of the gradient of fuel-based combustion progress variable indicate predominant thinning of reaction zones.