Stabilization of premixed hydrogen–air flames in a trapped vortex combustor

This study investigates flame stabilization and flashback in a trapped vortex combustor operating on a lean premixed hydrogen–air mixture at an equivalence ratio of ϕ=0.35. The combustor geometry features a U-bend in conjuction with a liner plate that aerodynamically stabilizes the flame. Particle Image Velocimetry (PIV) was used to study the (reacting) flow in detail at two Reynolds numbers: Re=9.68×10³ (case R-1, marginally stable flame) and Re=13.55×10³ (case R-2, highly stable flame). Within the U-bend, the flame front shows steady laminar-like behaviour where the velocity is primarily tangential to the flame front. Downstream of the U-bend, the shear layer weakens and the flame front becomes more intermittent. This intermittency may cause flame bulges to reach low-velocity zones near the U-bend wall, increasing the possibility of flame flashback through the boundary layer that wall. An analysis of the strain rate tensor shows that within the U-bend, the angle between the flame front normal and the most extensive strain rate direction remains close to 45°, indicating the dominance of shear straining in this region. Further downstream, alignment with the most extensive strain rate increases, indicating that combustion-induced expansion becomes more dominant.