Flame instability and heat transfer effect during deflagration of premixed hydrogen in tunnel

Abstract

In the process of hydrogen deflagration, thermal diffusion and fluid dynamics instability lead to the instability of premixed flames. With the enhancement of instability, the behavior of the flame front becomes unstable, leading to an increase in flame surface area and flame speed. This study used the three-dimensional full-speed CFD code GASFLOW-MPI to perform numerical simulations of tunnel model deflagration experiments based on the compressible Navier-Stokes equations. The turbulent combustion model used in the study takes into account the effects of thermal diffusion instability, fluid dynamics instability, and local turbulent disturbances. This paper quantitatively calculates the thermal diffusion and fluid dynamics instability to explore their effects on developing tunnel premixed hydrogen deflagration flames. Based on the effective Lewis number of the unburned premixed gas of the flame front and the ratio of thermal expansion to the flame thickness, the interaction behavior between them is analyzed. Additionally, this paper explores in depth the influence of heat transfer boundary conditions on the propagation of flame instability. Results show that the calculation results of the combustion model considering heat transfer effects are highly consistent with the experimental values, demonstrating the importance of heat loss in the overpressure peak and pressure decay process. During the deflagration process, thermal radiation plays a leading role, while heat convection makes the main contribution to heat loss during pressure decay. As the flame evolves, the destabilizing effect of fluid dynamics instability first increases and then decreases, while the stabilizing effect of thermal diffusion instability gradually weakens and transitions to a destabilizing effect, with both effects mutually reinforcing each other. Heat transfer effects delay mixing hydrogen-premixed gases with fresh air, slowing the transition of thermal diffusion instability from stability to instability, weakening the destabilizing effect of fluid dynamics instability, and thereby delaying the evolution process from competition to promotion between the two.