Supplementary information files for "Turbulent flame–wall interaction of thermodiffusively unstable lean premixed hydrogen flames"

For hydrogen, the wall heat flux is found to increase by approximately an order of magnitude with dimensionality and turbulence intensity (Karlovitz number), accompanied by a corresponding decrease in quenching distance. In contrast, large-scale flame wrinkling (Damköhler number) has no discernible effect on the quenching process under the conditions investigated. Furthermore, the effects of the TD response on the quenching behavior are consistent between maintained- and decaying-HIT cases.

Finally, wall heat fluxes and quenching distances are normalized using freely propagating (turbulent) flame properties (instead of 1D laminar values) to account for TD effects, enabling a more meaningful comparison of key quenching parameters (normalized quenching wall heat flux and Péclet number) between hydrogen and methane.</p><p dir="ltr"><i>Novelty and significance statement:</i> This work provides the first systematic 3D DNS study of the interplay between thermodiffusive (TD) effects and turbulence in lean premixed H₂ head-on quenching, varying Karlovitz (<i>K</i><i>a</i>) and Damköhler (<i>D</i><i>a</i>) numbers.

It is the first study to show that increasing <i>K</i><i>a</i> strongly amplifies wall heat flux and reduces the quenching distance, whereas <i>D</i><i>a</i> variations have negligible influence; unity-Lewis-number CH₄ reference flames exhibit no comparable turbulence sensitivity. Notably, these results establish that conventional normalization of quenching metrics (e.g., wall heat flux) with 1D laminar flame quantities is inadequate for lean turbulent H₂ flames; instead, freely propagating turbulent flame properties (e.g., mean local flame speed and thickness) should be used.

This proposed normalization is particularly relevant for the design of practical combustors, which typically operate under turbulent flow conditions and are confined by walls, since the strong increase in heat flux and the reduced quenching distance directly affect durability and thermal management.<br><br>© The Author(s), CC BY 4.0</p>