Explicit Simulation of Small Scales in Chemically Reacting Turbulent Flows using the Two-Level Simulation Model

Numerical investigation of chemically reacting turbulent flows tends to be computationally expensive due to the need to capture the multiscale flame turbulence interactions. Although significant advancements have been made in model-based approaches, there is still a need for a robust and predictive model for such flows under different operating regimes and conditions. In this study, we examine the capabilities of the two-level simulation (TLS) model. The model relies on a scale-decomposition strategy to obtain large-scale (LS) and small-scale (SS) governing equations, which is followed by simplification of the SS equations to express them on one-dimensional domains leading to an efficient simulation strategy. Unlike other models where the effects of unresolved SS dynamics are parametrized, in the TLS model, the SS flow field is explicitly simulated in a coupled manner with the LS flow field, thus leading to unique capabilities to capture the SS dynamics. We evaluate the performance of the TLS model by considering two challenging test cases, namely, a freely propagating turbulent premixed flame in the thin reaction regime and a temporally evolving non-premixed jet flame exhibiting local extinction and re-ignition events. First, we assess the validity of the SS modeling assumptions and the ability of the model to capture SS physics such as anisotropy, counter-gradient transport, scalar dissipation rate, etc. Afterward, we perform a posteriori assessment in terms of the evolution of SS quantities.