Numerical Simulation on the Influence of Pipe Section Size on Hydrogen Flame Propagation Process in Closed Pipe

Abstract

ABSTRACT In order to reveal the influence of pipe section size effect on hydrogen detonation characteristics, Large Eddy Simulation (LES) model was used to numerically investigate the hydrogen/air detonation process in closed space of different size. The results show that in the process of flame propagation, the reflection frequency of the shear wave produced by the small cross-section pipeline is higher, which increases the probability of the tulip flame and flame structure distortion. For a 6-m-long square-closed pipe, the influence mechanism of the cross-section size on the flame propagation is different at different stages of flame propagation. In the early stage of flame propagation (that is, in the pipe segment 0–0.8 m away from the ignition end), the internal friction caused by the friction between the flame and the tube wall increases the turbulent intensity of the flammable cloud and accelerates the flame propagation. In a confined space with the cross-section edge length of 100 mm, the maximum flame propagation speed is 176.7 m/s, which is 48.5% faster than that in the confined space with the cross-section edge length of 250 mm. In the middle of the flame propagation (that is, in the pipe segment 0.8-5m away from the ignition end), the flame area increases sharply during combustion and releases more energy. Therefore, larger vortices are formed, and the flame propagation is accelerated by turbulence efficiency. The maximum flame propagation speed can reach 500 m/s when the cross-section edge length is 250 mm, which is 140.8% faster than that when the cross-section edge length is 100 mm. In the later stage of flame propagation (that is, in the pipe segment 0.8–5 m away from the ignition end), the pressure in the pipe increases sharply, and the reflected wave from the pipe end produces great resistance to the propagation of the flame front, and the flame propagation speed decreases sharply in the pipeline of various cross-sections.