Large-eddy simulations of a lean hydrogen premixed turbulent jet flame with tabulated chemistry

Abstract

Large-eddy simulations (LES) of a planar turbulent lean hydrogen-air jet flame at Re = 11000 are performed using a tabulated flamelet model based on mixture-averaged diffusion that incorporates detailed transport, including differential and preferential diffusion, wall heat loss, and thermodiffusion. The approach is extended to turbulent combustion in LES using a presumed-shape probability density function formulation that accounts for sub-filter effects. The flame exhibits a highly corrugated front, driven by local variations of mixture fraction induced by strong thermodiffusive transport. These effects significantly alter both the flame structure and morphology. The LES results are systematically compared to a reference direct numerical simulation across varying LES filters through different mesh resolutions to evaluate the predictive capability of the model. The LES accurately reproduces instantaneous flow structures and thermodiffusive effects. Global flame characteristics including flame length, surface area, and consumption speed, are well captured and show limited sensitivity to mesh resolution. The role of thermodiffusion is also examined, showing that its incorporation leads to a more reactive flame and should not be neglected in the formulation. Heat losses are incorporated into the tabulated chemistry framework for completeness but are found to have a negligible impact, consistent with the walls weak influence in the present configuration. Overall, the results demonstrate that the proposed approach provides reliable predictions of the main flame characteristics, with remaining discrepancies primarily associated with unresolved sub-filter effects that deserve further investigation.

Figures (12)

• Figure 1: Instantaneous snapshots of mixture fraction (first two rows), temperature (rows three and four), and heat release rate (rows five and six) for the DNS and the LES M4 (upper and lower plots of each pair, respectively). Level curves of scaled temperature $T_s$=0.6 from Eq. \ref{['eq:norm_T']} are included on the first two rows to aid the visualisation.
• Figure 2: Instantaneous snapshots of the $Z$ for the DNS and $\widetilde{Z}$ for LES for each mesh resolution.
• Figure 3: Mean fields of the mixture fraction (first two rows), progress variable (rows three and four), and hydrogen source term (rows five and six) for the filtered DNS and the LES M4 (upper and lower plots of each pair, respectively). Level curves of scaled temperature $\langle T_s\rangle_{t,z}=0.6$ from Eq. \ref{['eq:norm_T']} are included to aid the visualisation.
• Figure 4: $\langle \widetilde{T} \rangle_{t,z}$ field for the DNS (first panel), the LES with different resolutions and all physics (second to fifth panels), the LES without Soret effect (sixth panel) and the LES without heat losses (seventh panel). Isocontours of $sT = 0.6$ from Eq.\ref{['eq:norm_T']} (cyan lines) and the DNS flame length $h_T$ are included for reference.
• Figure 5: of temperature (first row), hydrogen source term (second row) and mixture fraction (third row) with respect to the progress variable for the DNS (first column), LES with resolutions M4 and M1 (columns two and three), LES without Soret effect (column four) and LES without wall heat losses (column five). A maroon ellipse is added to the first row to aid visualisation and highlight the region affected by heat losses.