Scale effect of spherical projectiles for stabilization of oblique detonation waves
Scale effect of spherical projectiles for stabilization of oblique detonation waves
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DOI：
10.1007/s00193-015-0549-4
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发表时间：
2015-02
期刊：
影响因子：
2.2
通讯作者：
S. Maeda;S. Sumiya;J. Kasahara;A. Matsuo
中科院分区：
文献类型：
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作者：
S. Maeda;S. Sumiya;J. Kasahara;A. Matsuo
通过以1.2-1.4倍查普曼-朱盖（C-J）速度向静止的可爆混合物发射球形弹丸来稳定倾斜爆轰波（ODW）。我们使用更小的弹丸（3.18毫米直径）比那些（4.76毫米直径）在我们以前的研究和研究的影响，弹丸规模上的稳定ODWs。我们进行了高时间分辨率纹影可视化使用高速相机。所用的可引爆混合物是化学计量的氧与乙炔、乙烯或氢的混合物。将它们用50%体积分数的氩气稀释，并且还测试了含有75%氩气的稀释混合物的乙炔/氧气混合物。在这里，我们讨论了爆轰稳定性的曲率效应所产生的三维性质的稳定ODW周围的弹丸。曲率效应使爆轰波在弹丸附近衰减到C-J速度以下，然后爆轰波在远场渐近达到C-J速度。我们以前的研究表明，曲率效应的传播极限是负责稳定的临界爆轰波。通过获得稳定临界点处的波传播速度和曲率半径的详细分布，我们发现波传播速度的局部极小点处的曲率半径代表弯曲自持爆轰所需的临界曲率半径。在这项研究中，我们专注于这种临界模式的稳定ODW的小弹丸（3.18毫米直径）。得到了稳定ODW临界模态下的波速和曲率半径分布。我们比较这些分布与一个更大的弹丸（4.76毫米直径），并讨论了稳定的临界。对于小弹丸，所观察到的燃烧制度有定性相同的趋势，为大弹丸所观察到的混合物的初始压力。然而，每个燃烧制度的初始压力是定量不同的不同的弹丸规模。小弹丸比大弹丸需要更高的初始压力来稳定ODW。对于稳定ODW的临界模式，由于曲率效应，波速分布存在局部极小值（C-J速度的0.8-0.9倍）。无论混合物的成分如何，在这个特征点的曲率半径大约是射弹半径的五倍。对于用50%和75%氩气稀释的混合物，由单元尺寸归一化的曲率半径分别为约8-10和15，与射弹直径无关。这些结果意味着，弹丸半径（直径）成比例地影响波周围的弹丸的几何尺度，和用于稀释的气体的分数影响维持弯曲的爆震波所需的细胞大小。用无量纲射弹直径（射弹直径由单元尺寸归一化）表示的稳定临界性对于用50%和75%氩气稀释的混合物分别为约3.5和5.5。这些临界值与先前研究的大型射弹的临界值一致。这表明，无量纲弹丸直径是一个唯一的参数稳定临界，无论弹丸直径。
Oblique detonation waves (ODWs) were stabilized by launching a spherical projectile with 1.2–1.4 times the Chapman–Jouguet (C–J) velocity into detonable mixtures at rest. We used smaller projectiles (3.18 mm diameter) than those (4.76 mm diameter) in our previous studies and investigated the effect of the projectile scale on the stabilization of ODWs. We carried out high time resolution schlieren visualization using a high-speed camera. The detonable mixtures used were stoichiometric oxygen mixtures with acetylene, ethylene or hydrogen. They were diluted with argon with a 50 % volumetric fraction, and a dilute mixture containing 75 % argon was also tested for the acetylene/oxygen mixture. Here, we discuss the detonation stability in terms of the curvature effect arising from the three-dimensional nature of a stabilized ODW around a projectile. The curvature effect attenuated the detonation wave to below its C–J velocity in the vicinity of the projectile before the wave velocity asymptotically reached the C–J velocity in the far field. Our previous study showed that the propagation limit of the curvature effect is responsible for the stabilizing criticality of detonation waves. By obtaining detailed distributions of the wave propagation velocity and radius of curvature at the stabilizing criticality, we showed that the radius of curvature at the local minimum point of the wave propagation velocity represents the critical radius of curvature required for curved self-sustained detonation. In this study, we focused on this critical mode of the stabilized ODW for a small projectile (3.18 mm diameter). Distributions of the wave velocity and radius of curvature were obtained in the critical mode of the stabilized ODW. We compare these distributions with those for a larger projectile (4.76 mm diameter) and discuss the stabilizing criticality. For the small projectile, the observed combustion regimes had qualitatively the same trend for the initial pressure of the mixture as that observed for the large projectile. However, the initial pressure for each combustion regime was quantitatively different for the different projectile scales. The small projectile required a higher initial pressure to stabilize the ODW than the large projectile. For the critical mode of the stabilized ODW, the wave velocity distribution had a local minimum value (0.8–0.9 times the C–J velocity) due to the curvature effect. The radius of curvature at this characteristic point was about five times the projectile radius, regardless of the mixture composition. The radius of curvature normalized by the cell size was about 8–10 and 15 for mixtures diluted with 50 and 75 % argon, respectively, regardless of the projectile diameter. These results mean that the projectile radius (diameter) proportionally affects the geometrical scale of the wave around the projectile, and the fraction of the gas used for dilution affects the cell size required to sustain a curved detonation wave. The stabilizing criticality, expressed as the dimensionless projectile diameter (projectile diameter normalized by cell size), was about 3.5 and 5.5 for mixtures diluted with 50 and 75 % argon, respectively. These criticalities agreed with those of the large projectile of the previous study. This indicates that the dimensionless projectile diameter is a unique parameter for the stabilizing criticality regardless of the projectile diameter.