| 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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