Large eddy simulation and calculation of propagation characteristics of hydrogen flame under obstacle conditions

Abstract

[Objective] Compared with conventional gas fuel, hydrogen is more susceptible to explosion. Meanwhile, the existence of obstacles notably stimulates hydrogen combustion and accelerates flame propagation, causing more serious consequences of accidents. To reduce destructive damage caused by hydrogen combustion under obstacle conditions, it is particularly important to reveal the influences of different obstacle conditions on the characteristics of flame propagation of hydrogen. [Methods] Based on large eddy simulation, the hydrogen/air combustion and explosion processes under different obstacle shapes and blockage rate conditions were numerically simulated.Focus was given to the research on different flame propagation velocities caused by different obstacle shapes and the sensitivity to blockage rate changes. [Results] Under low blockage rate, grid-type obstacles had a stronger destructive effect on the regular flow field at the flame front than single-side obstacles, and as the number of voids in grid-type obstacles increased, their destructive effect on the flow field motion further intensified, making it difficult for the flame front to recover to a regular state. When the blockage rate went up, the difference of the shapes of obstacles became insignificant in causing damage to the regular flow field, and the flame front was continuously distorted under all obstacle conditions. As the blockage rate continued to increase, single-side obstacles brought higher peak flame propagation velocity than grid-type obstacles. At the same blockage rate, the mechanism of flame acceleration by grid-type obstacles can be changed by adjusting the single void area to enhance the acceleration effect. [Conclusion] The shape and blockage rate of obstacles are the key factors influencing the state of flame front behind obstacles.The single-side obstacle is more sensitive to the blockage rate,while the grid-type obstacle has higher acceleration potential.The research results provide basic reference data for the prevention and control of hydrogen fire accidents and serve as a reference for the design of hydrogen power systems.

Keywords

• hydrogen
• combustion
• obstacle
• blockage rate
• flame propagation
• flow field change
• flow velocity change