【作者】 李玲玲；

【导师】 李大鸣；

【作者基本信息】 天津大学 ， 水利工程， 2012， 硕士

【摘要】 自由表面流动问题在自然界中广泛存在,例如水利工程中的溃坝、自由表面溢流、明渠水流等,它无处不在影响着人类的生存和发展,因此自由表面流动的研究也具有十分重要的现实意义。液滴与固体壁面的碰撞是典型的自由表面流动问题。液滴与壁面碰撞后的扩散、回弹甚至破碎现象广泛地存在于化工制造、冶金技术等工业过程中,因此,研究液滴撞击固壁现象能更好地了解具有自由表面流动问题。本文采用拉格朗日形式的无网格粒子法—光滑粒子流体动力学方法(SPH)对液滴撞击固壁问题进行数值模拟研究。研究了适用于广义流体动力学的SPH的基本方程及与其相关的数值技术,由拉格朗日形式下的流体基本方程推导出SPH形式下的流体基本方程。通过采用人工压缩率,把所有理论不可压缩流体模化为实际上是弱可压缩的;通过采用人工粘性来消除计算结果产生的非物理振荡。采用SPH方法建立了二维液滴撞击固壁基本模型,对液滴撞击固壁后的动力学行为进行数值模拟,将数值模拟结果与物理实验结果进行对比分析;对撞击固壁后液滴内部流场、压强场、特征粒子的运动速度及位移情况进行分析研究;通过改变相关参数,如液滴的初始撞击速度、液滴的初始半径等,研究以上相关因素对液滴撞击固壁后铺展因素的影响;在此基础上,通过建立三维模型,来研究三维情况下液滴撞击固壁后的运动过程。建立液滴撞击固壁后运动状态的理论模型,研究分析液滴铺展因素与接触角间的关系及液滴的撞击速度与接触角间的关系,从而得到液滴的铺展因素与液滴的撞击速度之间的关系,并把理论推导结果与数值模拟结果进行对比分析。更多还原

【Abstract】 It exists extensively in nature for free surface flow, such as dam-break in hydraulic engineering, overflow in free surface and flow in open channels, which influences widely to the survival and development of mankind, so it’s of great significance to study free surface flow problem. A liquid droplet impacting on a solid surface is a classic free surface flow problem. The phenomenon of diffusion, rebound and broken of a droplet when it impacts on a solid surface exists extensively in chemical industry and metallurgical industry. It’s a good way to study free surface flow by studying the phenomenon of a droplet impacting on a solid surface.The Smoothed Particle Hydrodynamics (SPH) method is applied in the numerical simulation of a droplet impacting on a solid surface which is a Lagrangian meshfree particle method. The SPH equations and the key technology which are suitable to generalized hydrokinetics are studied, and the SPH fluid equations are derived from Lagrangian fluid equations. Artificial Compression is applied to calculate the time derivative of stress considering incompressible fluid as compressible fluid. Artificial viscosity is applied to eliminate unphysical oscillation in results. The treatment method of boundary conditions including rigid boundary and free surface boundary is studied, and so do the search of free surface particles, the choice of time steps and the searching method among neighboring particles.SPH method is applied to establish 2-Dimensional model to simulate a liquid droplet impacting on a solid surface. The comparison between the simulated results and experimental results is done, and the flow field, the pressure, the speed and displacement of the representative particles are all studied. The spreading factor is studied by changing the related parameters, such as initial velocity and initial radius of the droplet. Based on above analysis the 3-Dimensional model is established to study the motion of the droplet when it impacts on a solid surface.The theoretical model of a droplet impacting on a solid surface is established to study the relationship between spreading factor and contact angel, the relationship between impacting velocity of the droplet and contact angel, so the relationship between spreading factor and impacting velocity of the droplet can be got, which can be compared with numerical simulated results.更多还原