Numerical simulations of premixed hydrogen-air flame propagation in a pipe with different contraction or expansion angles are carried out in this study. The effects on the flame propagation characteristics are investigated, including flame shape, the speed of flame front and overpressure. Results show that the flame propagation at different contraction angles experiences 6 flame stages: spherical flame stage, finger-shaped flame stage, stage of flame front touching the sidewalls, classic tulip flame stage, dissipation stage of tulip flame and its re-formation stage. The formation of tulip flame and the following stages are promoted by the contraction structure. Meanwhile, the development of the flow and pressure fields near the contraction are analyzed and it is found that the paraclinical effects induced by the contraction angle enhance the tulip re-formation. In the sudden expansion pipes, a triple flame stage appears in the pipes. The flame front remains relatively static for a period of time. However, the flame would continue to propagate when the expansion angle becomes larger and the flame propagation distance in the ducts increased obviously with the larger expansion angle. Baroclinic effect can inhibit the intensity of the vortex in the flow field, and hence weaken the forward transport of fuel. This inhibit effects decrease with the expansion angle becomes larger. The results of this study have implications concerning designs for pipe geometry of hydrogen and may help get better hydrogen transportation.

在这项研究中进行了预混合氢-空气火焰在不同收缩或膨胀角的管道中传播的数值模拟。研究了对火焰传播特性的影响，包括火焰形状，火焰前沿速度和超压。结果表明，不同收缩角下的火焰传播经历了6个火焰阶段：球形火焰阶段，指状火焰阶段，接触侧壁的火焰前沿阶段，经典的郁金香火焰阶段，郁金香火焰的消散阶段及其再形成阶段。收缩结构促进了郁金香火焰的形成和随后的阶段。同时，分析了收缩附近流场和压力场的发展，发现收缩角引起的旁临床效应增强了郁金香的重组。在突然膨胀的管道中，管道中出现了三重火焰阶段。火焰前沿在一段时间内保持相对静止。然而，当膨胀角变大时，火焰将继续传播，并且随着膨胀角的增大，管道中的火焰传播距离明显增加。斜压效应可以抑制流场中涡流的强度，从而削弱燃料的向前输送。随着膨胀角变大，该抑制效果降低。这项研究的结果对氢气管道几何形状的设计有影响，并可能有助于获得更好的氢气运输。