Interactions of turbulence and flame during turbulent boundary layer premixed flame flashback under isothermal and adiabatic wall conditions using direct numerical simulation

Abstract

In this work, lean hydrogen/air premixed flame flashback in a turbulent boundary layer along an isothermal wall and an adiabatic wall was simulated using direct numerical simulation. The general characteristics of flame flashback were analyzed. It was found that the propagating speed along the adiabatic wall is higher than that along the isothermal wall. The displacement speed near the isothermal wall is notably lower than that near the adiabatic wall, primarily due to the smaller value of the reaction component of the displacement speed near the isothermal wall. Furthermore, the properties of the boundary layer turbulence during flame flashback were examined in terms of the flow topology and the anisotropy of Reynolds stress. It was observed that the focal topologies tend to prevail near the adiabatic wall, and the volume fraction of stable topologies increases near the isothermal wall due to the increased compressed region caused by the wall heat loss. Finally, the influence of turbulence on the flame structure was highlighted. It was suggested that the unstable topologies dominate the heat release rate away from the wall. The proportion of heat release rate in focal topologies increases near the adiabatic wall, and the proportion in stable topologies increases near the isothermal wall. The impact of the low temperature wall on the flame structure is more pronounced in topologies with compression compared to those with expansion.