摘要
枪炮发射时会形成复杂的膛口流场,炮口制退器的设计中需要对膛口流场特别是炮口制退器内部流场进行详细分析。不同复杂程度的膛口流场需要选用合适的算法进行模拟。
相对于整个后效期,弹丸飞离膛口的时间很短暂,如果不考虑运动弹丸的影响,膛口流场的数值模拟将得到很大简化。不带膛口装置或者带有锥形消焰器的膛口流场采用TVD有限体积法求解轴对称Euler方程进行模拟;对结构较简单的炮口制退器流场生成拼接的三维结构化网格,采用LU隐式因式分解方法和Jameson格式离散Euler方程求解;对于具有复杂结构的炮口制退器采用三维非结构网格和HLLC格式对火药气体排空过程进行数值模拟。
火炮发射过程中,弹丸和身管之间发生高速的相对滑动和分离,而分离的过程将导致流场拓扑结构的改变。针对三维流场拓扑结构的改变,对非结构重叠网格(OUG——Overset Unstructured grids)方法进行了改进。构造了确定非结构网格下洞边界的“曲面判定法”。叉树型数据结构具有很高的搜索效率,设计了“动态叉树”搜索算法用于“洞边界”(或网格间边界intergrid boundaries)上待插值点的贡献单元的搜索。解决了拓扑结构改变过程中重叠区域的建立和网格系之间流场信息的传递问题。采用OUG方法对弹丸与身管之间的高速滑动和分离过程进行了非定常数值模拟。
三维非定常流场的数值模拟带来巨大的计算量,并行计算技术是减少计算时间的有效工具,针对结构网格、非结构网格和OUG方法分别设计了三种并行算法。提出了基于多块拼接结构化网格的并行算法,建立了合理的网格分区策略,基于分区信息文件设计了通用的信息通信准则;由于非结构网格单元的空间分布具有很大灵活性,程序中采用单向链表对分区边界处的网格单元进行组织,建立了能适应任何分区拓扑结构的信息通讯准则;对于运动边界问题,随着流场中运动物体位置的改变,频繁进行网格的重新分区将耗费大量计算时间,针对OUG方法的特点设计了网格分区策略,不仅能避免网格分区的频繁重新划分,而且有利于提高重叠区中信息传递的效率,使程序得到简化的同时提高了其通用性。
以复杂流场的数值方法研究为基础,提出了新的炮口制退器设计计算方法。通过膛口流场的数值模拟获得后效期中带和不带炮口制退器时身管的受力变化曲线,计算身管的最大自由后坐速度,根据其物理定义计算炮口制退器的效率。针对某口径滑膛炮设计了一组炮口制退器,分别计算其效率并对各自冲击波场的发展过程进行分析。
本文建立了针对不同复杂程度膛口流场数值模拟的软件包。针对弹丸发射过程中流场拓扑结构的变化,对OUG方法进行了改进,并且有针对性地提出了高效的并行算法,可以有效地应用到航空、航天和兵器技术等领域的相关研究中。以复杂膛口流场数值模拟基础提出新的炮口制退器设计计算方法,将有助于新形势下火炮的整体设计。
Muzzle flow field formed after shooting is very complex. Detailed informations of a muzzle flow field, especially the flow field in the muzzle brake are necessary for designing the muzzle brake. Different methods are needed to simulate the flow field with different structures.
In the after-working period, projectile flies far from the the muzzle very fast. If the moving projectile is ignored, the simulation of muzzle flow field can be simplified greatly. Both of the muzzle flow fields with the action from a conical flame damper and without the action from any muzzle set are simulated using the TVD finite volume method to discrete the 2D axisymmetrical Euler equations. To simulate the flow field of the muzzle brake having simple structure, the Jameson difference scheme and the implicit LU factorization scheme are used to solve generalized Euler equations. Further more, the flow field with the action from a complex muzzle brake is simulated using unstructured grids and the HLLC scheme.
In a launching process, the relative sliding and departing takes place between a bullet and a barrel contacting with each other, and therefore topological structure of the flow field changes. An overset unstructured grid (OUG) method is proposed to simulate the changes of 3D flow field topological structure. A curved face criterion is proposed to define intergrid boundaries. The quadtree/octree search algorithm is efficient when used in the unstructured grids. A dynamic quadtree/octree search algorithm is proposed to search for donor cells of the nodes on the intergrid boundaries. The departure of the moving objects can cause persistent changes of flow field topological structure. The new OUG method can rebuild overset areas and transfer massages between subdomains in the departing process. The sliding and departing process between the bullet and the barrel is simulated by the OUG method.
It is a challenge to improve computing speed of simulating unsteady 3D flow field. However, the parallel computation technique is an effective tool to solve this problem. Three kinds of parallel algorithms are proposed for structured grids, unstructured grids and overset unstructured grids. In the parallel algorithm proposed for the structured grids, an effective domain partitioning method is proposed and a general communication criterion is accordingly proposed using the sub-domain information file. Because of the flexible spatial distribution of cells, the parallel algorithm of unstructured grids is more complex. In the program, unidirectional chained list is used to manage the cells located on the partition boundaries. The communication criterion based on the unstructured grids is available to simulate the flow fields with general sub-domain structures. If a moving object exists in the flow filed, it may cost much time to repartition the domain into sub-domains in the moving process of the object. To solve this problem, a special partitioning method is proposed according to the characteristic of the OUG method developed in this paper. Two kinds of message communications exist in using the parallel OUG method. One of them is the message communication on the partition boundaries, and the other one is that in the overlapped areas. By using the partitioning method proposed in the OUG method, the frequent repartitioning of the domain is avoided, and the efficiency of communications in the overlapped areas is improved.
A new method for designing muzzle brake is proposed based on the study of numerical method for simulating the complex muzzle flow fields. By recording the fluctuating force applied on the barrel, the maximum free backlash velocity of the barrel with or without the action from a muzzle brake can be calculated. Thus the efficiency of the muzzle brake can be obtained according to the definition. For the smooth bore artillery of a certain caliber, a series of muzzle brakes are designed according to different requirements. Further their efficiencies are calculated respectively, and the developing processes of the muzzle flow fields are also analyzed respectively.
A software package is built to simulate different muzzle flow fields. To simulate the changes of flow field topological structure, the OUG method is improved and a parallel algorithm is proposed for the OUG method. The parallel OUG method can be used in the studies of aeronautic, astronautic and weapon technology. A new method for designing a muzzle brake is proposed based on the simulation of complex muzzle flow field. This method is proved useful for promoting the design of the artillery.
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