2022 **Abstract:** Direct numerical simulation data obtained from two turbulent, lean hydrogen-air flames propagating in a box are analyzed to explore the influence of combustion-induced thermal expansion on turbulence in unburned gas. For this purpose, Helmholtz-Hodge decomposition is applied to the computed velocity fields. Subsequently, the second-order structure functions conditioned to unburned reactants are sampled from divergence-free solenoidal velocity field or irrotational potential velocity field, yielded by the decom…

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“…As the DNS attributes and data were reported earlier, 11,15,[46][47][48] only a brief description is given below, with more details being reported in Appendix A. Unconfined statistically 1D and planar, lean (the equivalence ratio Φ=0.7) H 2 -air turbulent flames were investigated by (i) adopting a detailed (9 species, 23 reversible reactions) chemical mechanism 49 with the mixture-averaged transport model and (ii) numerically solving unsteady three-dimensional governing equations, written in compressible form. Note that while differential diffusion effects are well known to be highly pronounced in very lean H 2 -air flames and to significantly increase turbulent burning velocity, as reviewed elsewhere, 38 differential diffusion was shown 50,51 to weakly affect a mean bulk burning rate at Φ=0.7.…”

confidence: 78%

“…As the DNS attributes and data were reported earlier, 11,15,[46][47][48] only a brief description is given below, with more details being reported in Appendix A. Unconfined statistically 1D and planar, lean (the equivalence ratio Φ=0.7) H 2 -air turbulent flames were investigated by (i) adopting a detailed (9 species, 23 reversible reactions) chemical mechanism 49 with the mixture-averaged transport model and (ii) numerically solving unsteady three-dimensional governing equations, written in compressible form. Note that while differential diffusion effects are well known to be highly pronounced in very lean H 2 -air flames and to significantly increase turbulent burning velocity, as reviewed elsewhere, 38 differential diffusion was shown 50,51 to weakly affect a mean bulk burning rate at Φ=0.7.…”

confidence: 78%

“…Accordingly, substantial influence of combustion-induced thermal expansion on turbulent eddies from the inertial range is expected. Indeed, two-point secondorder structure functions for the potential velocity field, which (i) were sampled from flame B, (ii) were conditioned to unburnt mixture, and (iii) were reported in a recent paper, 15 do show such an influence even at small distances 𝑟 between two points where velocity is picked.…”

confidence: 96%