Numerical simulation of hydrogen-air flame acceleration and detonation initiation in tubes equipped with arc obstacles of different chord lengths

Numerical simulation of hydrogen-air detonation characteristics in tubes equipped with arc obstacles of different chord lengths is carried out by using OpenFoam package. The results show the optimal chord length is half the diameter, in which the detonation wave propagates at a high velocity while maintaining small deflagration-to-detonation transition distance. Three different regimes were found in the flame acceleration and detonation initiation for different chord length: (1) For the small chord length, the flame experienced the transition from fingertip to tulip flame, then recovered to fingertip flame again until initiation. The detonation is caused by the hot spot formed by the spontaneous combustion of unburned premixed gas. (2) For the intermediate chord length, the tulip flame quenched by reverse flow will turn into fingertip flame under the jet effect of obstacles. Then, the fingertip flame is transformed into tulip flame again under the action of flow instability. The detonation is initiated by the fusion of two local hot spots produced by the coupling of tulip flame and diffraction wave. (3) For the large chord length, the flame propagates as a fingertip flame. The detonation is initiated by the explosion of the flame surface compressed by reflected wave and shock wave.