具有复杂几何壁面及流固耦合的移动接触线问题数值研究

发布时间：2018-03-08 18:16

  本文选题：移动接触线　切入点：复杂几何固体壁面　出处：《中国科学技术大学》2016年博士论文　论文类型：学位论文

【摘要】：带有移动接触线的复杂多相界面流动现象广泛存在于自然、日常生活和工业应用中。这类流动现象及其机理的研究具有重要的科学意义和广泛的应用前景。然而,由于涉及移动接触线、复杂几何形状固体壁面和流固耦合等因素,难以进行直接数值模拟,亟待数值模拟方法方面的研究。为此,本文发展了基于笛卡尔均匀网格的系列数值模拟方法,并针对具有复杂几何固壁及流固耦合的移动接触线问题进行了若干研究。主要工作及研究成果如下：(1)发展了蚀刻多块多相方法用来处理带有尖角的固体壁面上的移动接触线问题。该方法结合了扩散界面模型、几何形式的移动接触线模型及多块划分思想。扩散界面模型和几何形式的移动接触线模型能够模拟带有移动接触线的大密度比的多相流动问题；多块划分思想可以实现块与块之间信息的自然交换并能有效地施加并行方法。通过方柱绕流和小孔滴水问题验证了该方法的准确性。我们采用蚀刻多块多相方法对小孔滴水问题进行了研究,发现当接触线钉扎在尖角时,随着的We数增大会依次出现四种周期性滴落模态：带有卫星液滴的滴落模态、单周期滴落模态、双周期滴落模态和射流模态；当接触线可以跨过尖角自由移动时,液滴不容易出现周期性滴落现象,只有在We数较小时会出现带有多个卫星液滴的周期滴落模态。(2)发展了扩散界面-浸入边界数值方法用来模拟弯曲固体壁面上的动态浸润问题。该方法基于笛卡尔均匀网格,结合了三相扩散界面模型、浸入边界法和特征线法移动接触线模型。三相扩散界面模型能够防止液相和气相因为扩散而渗透到固相中；浸入边界法能够在壁面上准确施加无滑移条件,从而使得气液两相无法因为对流而穿透固体壁面。这两点的结合有效地保证了计算过程中各相的质量守恒性。特征线法移动接触线模型不仅可以让接触线自由移动,还可以让接触线在切向随空间变化的壁面上能保持设定的角度。为了验证该方法的准确性,我们模拟了一系列算例：圆柱上液滴平衡、平板上液滴动态润湿过程、液滴撞击圆球和液滴穿透多孔介质。我们采用所发展的扩散界面-浸入边界数值方法研究了圆球入水问题,发现随着圆球壁面上接触角的增大,入水后会依次出现三种模态：完全浸没,气泡附着以及产生空腔；同时发现We数也会影响入水后模态,随着We数的增大,越来越容易出现产生空腔的模态。(3)提出了适用于移动固体上的混合毛细力模型,基于扩散界面-浸入边界数值方法,发展了界面-流固耦合数值方法用来模拟流体界面与固体之间的相互作用。混合毛细力模型可以准确计算流体界面对固体施加的毛细力：当界面处于平衡状态时,采用锐利界面毛细力模型；当界面处于非平衡状态时,采用扩散界面毛细力模型。我们模拟了一系列算例来验证该方法的准确性：单相圆柱匀速下沉、重力影响下圆球上的轴对称液滴的平衡状态、界面上圆柱自由下沉、液滴与自由圆球正面碰撞和界面上漂浮圆柱自组装问题。我们还采用界面-流固耦合数值方法,在与前人实验定量对比良好的基础上,研究了密度大于水的疏水圆球撞击水面后的下沉模态和反弹模态,尤其是圆球表面浸润特性和水域宽度的影响,并且给出相应的尺度律。通过理论分析和数值模拟都得到了一致的结果：在足够宽的水域中,下沉与反弹的临界转换条件受到圆球表面浸润性(即接触角θ)的影响：而在有限水域宽度下(小于2倍圆球直径),We～sin(θ/2)4;临界转换条件还受到水域宽度L的影响：其中kWe～(C(θ,k)L+D(k)L-1)2,是唯一拟合参数。(4)将双网格方法推广至移动接触线问题的数值模拟,进一步提高界面的网格分辨率,同时发展了高效求解压力泊松方程的多重网格方法。结果显示两种加速方法都能大幅提升计算效率,均能提速达到80%以上。
[Abstract]:The complex flow phenomena with multi phase interface moving contact line widely exists in nature, daily life and industrial applications. This kind of flow phenomenon and its mechanism are of great scientific significance and wide application prospect. However, because of the moving contact line, the complex geometric shape of solid wall and fluid solid coupling and other factors. It is difficult to direct numerical simulation research to numerical simulation method. Therefore, this paper developed a series of numerical simulation method of Descartes based on uniform grids, and do some research for the moving contact line with complex geometric solid wall and fluid solid coupling problems. The main work and research results are as follows: (1) the development of the mobile contact a plurality of multi phase line etching method used to deal with the sharp corners of the solid wall on the surface of the problem. This method combines the diffusion interface model, moving contact line geometry model and multi Block partition. Diffusion moving contact line interface model and geometry model can simulate the moving contact line with large density ratio of multiphase flow; multi block partition can realize the information exchange between blocks of natural and can be effectively applied in parallel method. The accuracy of this method was verified by flow around a square cylinder and a small problem. We use water multiphase method of etching a plurality of holes in water was studied, and found that when the contact line pinning at a sharp point, with the increase in the number of We conference there are four kinds of periodic dripping mode: with dripping mode of satellite droplets, single cycle dripping mode, double cycle and dripping mode jet mode; when the contact line can move freely across the corner when the droplet is not prone to periodic drop phenomenon, only when the We number is small will appear with the cycle of dropping multiple satellite droplet model State. (2) the development of dynamic diffusion interface - immersed boundary numerical method is used to simulate the bending on solid wall infiltration problem. This method based on Descartes uniform grid, combined with the phase diffusion interface model, the immersed boundary method and characteristic line method of moving contact line model. The three-phase interface diffusion model can prevent liquid phase and gas phase because the diffusion and penetration into the solid phase; the immersed boundary method can accurately applied no slip conditions at the wall, so that the gas-liquid two-phase convection cannot because and penetrate the solid wall. The combination of the two can effectively ensure the quality of conservation of each phase in the process of calculation. The characteristic method can not only make the moving contact line model of contact line freedom of movement, also can make the contact line can maintain the set angle in the tangential changes of the wall. In order to verify the accuracy of the method, we simulate a series of examples: cylinder Droplet balance plate droplet dynamic wetting process, droplet impact ball and droplet penetration of porous media. The diffusion interface - we use the numerical method to study the immersed boundary ball into the water, found that with the increase of the contact angle on the wall surface of the ball, water will be followed by three modes: completely immersion, bubble attachment and cavity; also found that the We number will also affect after entry mode, with We number increasing, more and more prone to produce a cavity mode. (3) presents a hybrid capillary force model for mobile solid, diffuse interface - immersed boundary numerical method based on the development of the interface fluid solid coupling numerical method is used to simulate the interaction between fluid and solid interface. Mixed capillary force model can accurately calculate the capillary force of the solid fluid interface applied: when the interface is in balance, with a sharp circle The surface of capillary force model; when the interface is in a non-equilibrium state, the diffusion interface capillary force model. We simulate a series of examples to verify the accuracy of this method: single cylinder sinking speed, under the influence of gravity on the axisymmetric spherical droplet equilibrium interface cylindrical free sinking, self assembling problem solution drop ball head-on and with free interface. We also adopt the floating cylinder interface - flow solid coupling numerical method, based on comparing with previous experimental quantitative good, the hydrophobic ball density greater than water hit the water after sinking mode and rebound mode, especially on the surface of the sphere and the width of the water infiltration characteristics. The scaling laws, and gives corresponding. Through theoretical analysis and numerical simulation are consistent with results in the wide waters, critical transition condition and rebound of the sinking by the surface of the sphere 娴告鼎鎬，

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