Influence of Bend Structure on Air ShockwaveGenerated from Gas Explosion in theStraight Tunnel before the Bend

The bend structure is one of the most basic building elements of a coal tunnel.A good understanding of its influence on the gas explosion is essential for estimating the tunnel's blast resistance and thus for optimizing the tunnel's design.In the present work, we studied the influence of the bend structure on shockwaves in the straight tunnel before and at the bend under premixed methane-air explosion using numerical simulations.The shockwave propagation in the straight tunnel before the bend was analyzed.For a one-bend tunnel, the closer to the bend, the more obvious the difference between the impulse at this location and that at the same location in a straight tunnel.For tunnels with different bend angles, the larger the bend angle, the greater the change in the impulse compared with that at the corresponding location in a straight tunnel.Based on the influence of the reflected shockwave on the original shockwave in the straight tunnel before the bend, the relation of the critical scaled distance with the bend angle was established.At the bend, as the bend angle increases, the impulse here increases, and its increase percentage compared with that at the corresponding location in a straight tunnel changes as well, whose relation was also proposed.