非球形颗粒流的模拟程序开发及其对颗粒射流的模拟

Worthington jets, namely narrow vertical jets, are produced by the impacting liquid drops upon puddles surface. Similar narrow jets occur even for granular materials, where surface tension is absent. Obviously, the composition of these particles, e.g. shape, coefficient of restitution, surface roughness, density and so on, may affect the jet. This program is planned to discover the relationship between the macroscopically behavior and microscopically behavior by studying this kind of behavior in granular jets composed of non-spherical particles by both simulations and experiments. In addition, a program for complex granular flow will be set up via this program. Discrete element method (DEM) will be employed for the simulation of solid phase and SPH (smoothed particle hydrodynamics) a meshless method for the surrounding fluid phase. In addition, these two phases will be coupled in the simulations. In addition, the shape of the particles will be developed from spherical to non-spherical. As particle number, in 3D simulations, is huge, GPU technic will be used to speed the simulations. Excluding the simulations of granular jet, the codes can be used in other fields， e.g. the suspention of solid particles from liquid and so on. Lastly, the applicant want to release his previous codes and the new codes as free and open software under GNU general public License.

液滴冲击液面过程会形成飞溅射流，即Worthington 射流. 和液体相比，颗粒材料没有表面张力，但也会有类似的现象发生.显然由于粒子特性差异，如形状、回弹系数、表面摩擦等会影响射流的形态. 本项目希望通过数值模拟和实验相结合的方法， 以研究因为冲击造成不同性质的颗粒飞溅的不同表现为切入点, 研究非球形颗粒微观表现和宏观表现间的联系,同时编写一套用于复杂颗粒流计算的程序. 其中颗粒相采用离散元方法(DEM)模拟，而周围流体采用基于无网格的SPH或者其他CFD方法模拟，并且将两者的作用力双向耦合起来.同时将颗粒相内相互作用从球形粒子接触模型扩展到非球形粒子接触.由于复杂情况下(比如三维模拟下)颗粒数目巨大，拟采用 GPU 加速来求解.所编写程序除模拟射流外，今后还可用于其他领域，比如流场中颗粒的沉降分离.最后，申请人希望在 GNU 协议下将所开发程序开源.

颗粒物质是日常生活和工业生产中常见的物质形态，但是一般的连续介质假说并不适用于颗粒物质。离散元方法是一种常见的对颗粒流动进行数值仿真的方法。现在市面上有不少商业化和开源的离散元软件。但这些软件大多是欧美国家开发的，而且对于使用者而言，中间的具体计算过程不可见。而且对使用者而言，很难在现有程序的基础上对程序涉及的模型，计算方法等做合理的修改。为了弥补这一空白，本项目在项目负责人之间二维软件的基础上进行了开源软件ADEM的开发。在国家自然科学基金委的资助下，目前该软件可以对一些简单边界环境下的非球形颗粒进行数值仿真。并且可以和一些CFD软件耦合，对流固两相问题进行仿真。在本项目开展期间，负责人及其团队共发表了论文8篇，其中SCI论文3篇，培养硕士研究生两人。目前尚有博士、硕士研究生各一人在读。