Detonation diffraction has been extensively studied because it is a very fundamental problem and has broad practical applications. In this study, two-dimensional simulations considering detailed chemistry and transport are conducted to investigate the weakly unstable detonation diffracting through an obstacle. The emphasis is placed on assessing the effects of obstacle size and shape on detonation diffraction. For a semicircular obstacle, the subcritical, critical, and supercritical regimes are identified by increasing the obstacle radius. The competition between the energy release rate and expansion rate is analyzed; it interprets the regime distribution. Increasing the radius of a semicircular obstacle can reduce the curvature and thereby the expansion rate. The energy release rate dominates over the loss due to expansion during the diffraction process with a large obstacle radius. For triangular and rectangular obstacles, the supercritical regime without detonation quenching is not observed in the present simulations. Furthermore, the critical regime for transverse detonation formation is investigated and the critical obstacle sizes are compared for different obstacle geometries. It is found that the semicircular obstacle has the smallest critical size while the rectangular obstacle has the largest critical size. Unlike the critical obstacle size, the wall reflection distance of transverse detonation is independent of the obstacle geometry and it varies in the range of 10–15 times the detonation cell width. The characteristics of transverse detonation are compared for two weakly unstable mixtures, hydrogen/air without and with nitrogen dilution. A pair of transverse detonations induced by local explosion is observed in hydrogen/air with nitrogen dilution, which is quite different from the single transverse detonation in hydrogen/air. The comparison of the three regimes’ distributions for these two mixtures shows that a larger obstacle size is required for transverse detonation formation in hydrogen/air with nitrogen dilution. However, the critical obstacle size normalized by the corresponding detonation induction length becomes closer for two mixtures. This indicates that the formation of transverse detonation is nearly independent of nitrogen dilution for weakly unstable mixtures.

中文翻译：

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通过大小和形状不同的障碍物对弱不稳定爆炸的绕射

爆轰衍射已经被广泛研究，因为它是一个非常基本的问题，具有广泛的实际应用。在这项研究中，考虑到详细的化学和运输进行了二维模拟，以研究通过障碍物的弱不稳定爆轰衍射。重点放在评估障碍物尺寸和形状对爆炸衍射的影响。对于半圆形障碍物，通过增加障碍物半径来确定亚临界，临界和超临界状态。分析了能量释放率与膨胀率之间的竞争；它解释了政权的分布。增加半圆形障碍物的半径可以减小曲率，从而减小膨胀率。能量释放率在具有较大障碍物半径的衍射过程中的膨胀过程中占主导地位。对于三角形和矩形障碍物，在本模拟中未观察到没有爆震淬火的超临界状态。此外，研究了横向爆轰形成的临界状态，并比较了不同障碍物几何形状的临界障碍物尺寸。发现半圆形障碍物具有最小的临界尺寸，而矩形障碍物具有最大的临界尺寸。与临界障碍物尺寸不同，横向爆炸的壁反射距离与障碍物的几何形状无关，并且在爆炸单元宽度的10–15倍范围内变化。比较了两种弱不稳定混合物的横向爆震特性，氢气/空气，无氮气稀释和氮气稀释。在氢气/空气中，用氮气稀释后，观察到了由局部爆炸引起的一对横向爆炸，这与氢气/空气中的单个横向爆炸是完全不同的。对这两种混合物的三种态分布的比较表明，在氢气/空气中用氮气稀释形成横向爆轰时，需要更大的障碍物尺寸。但是，对于两种混合物，通过相应的爆轰诱导长度归一化的关键障碍物尺寸变得更近。这表明对于弱不稳定混合物，横向爆轰的形成几乎与氮稀释无关。这与氢气/空气中的单次横向爆轰有很大的不同。对这两种混合物的三种态分布的比较表明，在氢气/空气中用氮气稀释形成横向爆轰时，需要更大的障碍物尺寸。但是，对于两种混合物，通过相应的爆轰诱导长度归一化的关键障碍物尺寸变得更近。这表明对于弱不稳定混合物，横向爆轰的形成几乎与氮稀释无关。这与氢气/空气中的单次横向爆轰有很大的不同。对这两种混合物的三种态分布的比较表明，在氢气/空气中用氮气稀释形成横向爆轰时，需要更大的障碍物尺寸。但是，对于两种混合物，通过相应的爆轰诱导长度归一化的关键障碍物尺寸变得更近。这表明对于弱不稳定混合物，横向爆轰的形成几乎与氮稀释无关。对于两种混合物，由相应的爆轰诱导长度归一化的临界障碍物尺寸变得更近。这表明对于弱不稳定混合物，横向爆轰的形成几乎与氮稀释无关。对于两种混合物，由相应的爆轰诱导长度归一化的临界障碍物尺寸变得更近。这表明对于弱不稳定混合物，横向爆轰的形成几乎与氮稀释无关。