Numerical simulation of a muzzle flow field involving chemical reactions based on gridless method
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摘要: 基于无网格方法，对包含大位移运动边界和非平衡化学反应的膛口流场进行了数值模拟。所发展算法是基于线性基函数最小二乘显式无网格方法，忽略黏性及湍流的影响，对流场采用ALE(arbitrary Lagrangian-Eulerian)形式的Euler方程描述，对流通量和化学反应源项采用多组分HLLC(Harten-Lax-van Leer-Contact)格式和有限速率反应模型计算，对于运动边界造成的点云畸形采用局部点云重构方法处理，重构过程中采用虚拟边阵面推进。对圆柱绕流和激波诱导燃烧流场进行了数值模拟，验证了重构方法和化学反应计算的有效性。最后对12.7 mm口径机枪膛口流场进行了模拟，结果同实验照片、非结构网格方法结果吻合较好，数值结果清晰地再现了膛口初始冲击波、膛口冲击波、欠膨胀射流波系结构的动力学发展过程，以及膛口焰的时间、空间分布特征。Abstract: A gridless method for simulation of reactive flows involving moving boundaries was investigated based on the linear basis least-squares gridless method. The Euler equations of arbitrary Lagrangian-Eulerian form were employed as governing equations. The numerical flux and chemical sources were calculated by the multi-component HLLC ((Harten-Lax-van Leer-Contact) scheme and finite rate reaction model, respectively. An elevated restructuring technique of local cloud was adopted to deal with the moving boundaries. The front advance method of fictitious boundaries was used during the restructuring. The flow around the cylinder and the shock-induced combustion flow field were simulated to validate the accuracy firstly. The muzzle flow of a 12.7 mm machine gun was simulated. The computational shadowgraphs agree well with the experimental photographs, the density and pressure contours are in agreement with the results by the unstructured mesh method. The numerical results show the coupling and interaction progress in the initial muzzle flow field, the under-expanding jet of explosive gas and high-speed projectile clearly, and the temporal, spatial distribution characteristics of the muzzle flash are reappeared plainly.
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图 2 圆柱上表面量纲一压力分布
Figure 2. Distribution of the dimensionless pressure along the upper surface of the cylinder
图 4 驻点流线上温度、压力分布
Figure 4. Distribution of temperature and pressure along the stagnation stream line
图 5 驻点流线上组分质量分数
Figure 5. Distribution of mass fractions along the stagnation stream line
图 6 膛口离散点分布示意图
Figure 6. Schematic diagram for the distribution of the discrete points at the muzzle
图 7 弹丸出膛前不同时刻流场温度分布
Figure 7. Temperature contours in the flow field at different times begore the bullet leaves the muzzle
图 8 计算阴影图与实验阴影照片比较
Figure 8. Computational shadowgraph compared with experimental shadowgraph
图 10 不同时刻温度(上)和OH质量分数(下)分布云图
Figure 10. Temperature contours (top) and mass fraction contours f OH (bottom) at different times
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