Numerical Investigation of the Effects of Blockage Ratio and Obstruction Geometry on Flame Acceleration and Overpressure of Gas Explosion

The aim of the present paper is to investigate the effects of obstacles with different blockage ratio and geometry on flame acceleration and overpressure of premixed flame propagation using large eddy simulation. The subgrid-scale reaction rate is represented by the Flame-wrinkling combustion model developed by Weller. For the purposes of this paper, three different obstacles with circular, triangular and square cross-sections are studied here covering blockage ratios ranging from 10% to 72%. It is found that square and circular obstacles, result the fastest and the slowest flame acceleration, respectively. Velocity of jet-like flow around the obstacles and the level of turbulence generated by obstacles are increased with increasing blockage ratio and caused an increase in flame speed. The amount of unburned mixture trapped behind the obstacles, that plays a significant role in the overpressure, is found to be the highest for triangular obstacles.The maximum overpressure increases with increasing blockage ratio, but the rate of increase depends on the obstacle geometry. The square obstacles lead to highest overpressures while the circular ones produce the lowest overpressure. The time needed to reach the maximum overpressure decreases with increasing blockage ratio and depends on the obstacle geometry.