摘要
应用数值模拟方法研究不同尺寸单一液滴碰撞常温多孔介质内壁面时的运动与变形行为.界面跟踪采用基于VOF的体跟踪模型,简化的多孔介质结构应用孔隙网络模型.主要考查了初始液滴碰撞动能、表面能及液滴与多孔介质内壁面相对尺寸大小对液滴碰壁现象的影响,分析了液滴在多孔内壁面上形成液膜、液膜延展碰撞喉道壁面及飞溅破碎等过程的动力学特性.计算结果表明,液滴在多孔介质内的碰壁与在碰撞空间内大平壁的碰壁有很大差别.由于多孔介质结构特性,液滴碰壁后,除了通常的附着成膜和飞溅等情况外,还可能出现液膜沿壁铺展并跃出边界,从而在喉道内发生空间二次雾化现象;甚至还会发生子液滴与其他壁面进行二次碰撞并进一步雾化的现象.液滴初始动能越大,则孔穴内表面的油膜越薄,飞溅形成的子液滴越小,数量越多,分布越广.这些都为促进燃料-空气均质混合气的形成,改善发动机的燃烧与排放特性提供了条件.
The paper presents the results of a numerical study on the impingement process of a droplet onto a cell wall inside porous medium. The numerical method is based on the finite volume solution of the Navier-Stokes equations coupled with the volume of fluid method （VOF）. The porous medium structure was described using a pore-network model. The effects of initial impact energy, surface energy and the ratio of surface size to initial droplet diameter on droplet impingement were studied. The complex physical phenomena including droplet impinging, spreading and film formation on wall surface as well as splashing in cell space within the porous medium were examined. Results indicate that the impact of droplet on the porous medium is very different from that on a large solid surface. It is found that, with small impact energy, the droplet may deposit on the surface and form a liquid film, while with high impact energy, the film can spread over the edge of wall and splash into the throat space to form a number of childdroplets. The splashing trend becoiales stranger with the increase of droplet diameter and impingement velocity and the decrease of wall size. With the increase of initial impact energy of droplet, the film on the surface gets thinner, the size of secondary droplets becomes smaller, while their number grows larger, and their distribution gets more extended in space. These are beneficial to the formation of homogeneous fuel-air mixture and to the improvement of engine combustion and emission characteristics.
出处
《燃烧科学与技术》
EI
CAS
CSCD
北大核心
2011年第4期287-294,共8页
Journal of Combustion Science and Technology
基金
国家自然科学基金资助项目(50876017
50906007
51076109)
关键词
液滴碰壁
液滴飞溅
液膜
多孔介质
表面张力
droplet impact
droplet splash
film
porous medium
surface tension
