Energy & Fuels, Vol.29, No.10, 6815-6822, 2015
Effect of Pressure Oscillations on Flashback Characteristics in a Turbulent Channel Flow
A flashback phenomenon is reproduced by a direct numerical simulation (DNS) of a premixed hydrogen-air flame in a turbulent channel flow, and effects of the pressure oscillation, is caused by a virtual combustion instability on the flashback characteristics, are investigated. In addition, the interaction between the flashback flame structure and the turbulent flow structure is examined in detail. For the hydrogen air reaction, a chemical reaction model, which considers 9 chemical species and 20 reactions, is employed. The results show that the pressure oscillation strongly affects the flashback characteristics, such as the flashback speed and heat flux on the wall, and is at risk for increasing the flashback speed, because the acceleration of the flashback speed by the pressure oscillation is greater than the deceleration of it. Independent of the pressure oscillation, the turbulent eddies passing through the flame tend to be suppressed and vanish by the acceleration of the streamwise flow caused by thermal expansion. However, other turbulent eddies are generated again in a form of longitudinal eddies behind the flame only at the cusps and center of the channel where the upper and lower flames meet, because of the strong fluid shear owing to the thermal expansion.