Simulations of Boundary Layer Flashback in Hydrogen Flames

Hydrogen fuel has rapidly become a frontrunner in the search for carbon-free fuels. However, use of hydrogen in practical combustors is currently limited by several challenges including boundary layer flashback. A recent study has developed a critically-strained flashback model that accurately predicts the onset of boundary layer flashback using strained premixed flame properties at the extinction limit. However, the fundamental physical mechanism linking boundary layer flashback with strained flames at their extinction limit remains unclear. This work seeks to better understand this link by performing Direct Numerical Simulations of turbulent lean hydrogen at flashback conditions. In particular, simulations are performed at equivalence ratios just below and just above the flashback limits to understand how flame front behavior differs between stable flames and flashback. Analysis of these simulations provides insight into the relevance of strained flame extinction to flashback.