Large eddy simulation study on the tempered turbulent boundary layer

This study employs the large eddy simulation (LES) method combined with the flamelet generated manifold (FGM) combustion model to numerically investigate the phenomenon of boundary layer flashback in hydrogen/air mixtures within an unconfined space. The simulation results show that when the unconfined space boundary layer flashback occurs, the flame needs to overcome the wall heat loss to enter the burner interior. Moreover, before the flame enters the upstream pipe in the unconfined space, the interaction between the flame, the incoming flow, and the wall is weak, and there is no near-wall recirculation zone mechanism to promote the occurrence of flashback, which may lead to the fact that the unconfined space boundary layer flashback is more difficult to occur compared to the confined space. Meanwhile, due to the absence of boundary closure and the presence of complex non-equilibrium effects, the current LES models for unconfined spaces remain insufficient. Based on the numerical research results and further theoretical analysis, a Damköhler number correction model was proposed in this study. This model comprehensively considers the influence of a series of parameters, such as the burner edge temperature, laminar flame speed, and mixture properties on the boundary layer flashback. By comparing with the experimental data, the prediction results of the Damköhler number correction model are in good agreement with the experimental data in the literature, indicating that this correction model has an accurate prediction ability for the unconfined space turbulent boundary layer flashback.