Droplet spreading and capillary imbibition in a porous medium: A coupled IB-VOF method based numerical study
Droplet spreading and capillary imbibition in a porous medium: A coupled IB-VOF method based numerical study
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DOI：
10.1063/1.5010716
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发表时间：
2018-01-01
影响因子：
4.6
通讯作者：
Kuipers, J. A. M.
中科院分区：
文献类型：
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作者：
Das, Saurish;Patel, H. V.;Kuipers, J. A. M.
我们用孔尺度的全分辨数值模拟方法研究了液滴与多孔结构表面接触的动力学。在笛卡尔网格上采用锐面浸没边界法求解固体多孔基质的几何细节，而用质量守恒的流体体积法跟踪气液界面的运动。数值模拟是考虑一个模型多孔结构，该结构由一个带有圆柱支撑的三维立方体脚手架来近似。研究了孔隙率和平衡接触角(气液界面和固体支柱之间)对扩散行为、液体渗吸和表观接触角(气液界面和多孔基质之间)的影响。作为参考情况，我们还对液滴在平面上的扩散进行了几次模拟。拉普拉斯数La=45和La=144×10~(3)的气液体系被认为忽略了重力的影响。我们报道了描述不同平衡接触角和孔隙率的扩散直径(S=Ct(N))演化的幂定律的时间指数(N)和前因子(C)。模拟结果表明，表观接触角或宏观接触角随平衡接触角呈线性变化，随孔隙率增大而增大。对于所有润湿的多孔结构，不一定都会发生连续的毛细管引流，我们发现毛细管引流的速度很大程度上取决于流体的惯性。当La=144×10(3)时，数值模拟捕捉到了毛细管波诱导的夹断和子液滴抛射。我们观察到，与平板上的夹持相比，多孔结构上的夹断较弱。由AIP出版公司出版。
We investigate the dynamics of a liquid droplet in contact with a surface of a porous structure by means of the pore-scale level, fully resolved numerical simulations. The geometrical details of the solid porous matrix are resolved by a sharp interface immersed boundary method on a Cartesian computational grid, whereas the motion of the gas-liquid interface is tracked by a mass conservative volume of fluid method. The numerical simulations are performed considering a model porous structure that is approximated by a 3D cubical scaffold with cylindrical struts. The effect of the porosity and the equilibrium contact angle (between the gas-liquid interface and the solid struts) on the spreading behavior, liquid imbibition, and apparent contact angle (between the gas-liquid interface and the porous base) are studied. We also perform several simulations for droplet spreading on a flat surface as a reference case. Gas-liquid systems of the Laplace number, La = 45 and La = 144 x 10(3) are considered neglecting the effect of gravity. We report the time exponent (n) and pre-factor (C) of the power law describing the evolution of the spreading diameter (S = Ct(n)) for different equilibrium contact angles and porosity. Our simulations reveal that the apparent or macroscopic contact angle varies linearly with the equilibrium contact angle and increases with porosity. Not necessarily for all the wetting porous structures, a continuous capillary drainage occurs, and we find that the rate of the capillary drainage very much depends on the fluid inertia. At La = 144 x 10(3), numerically we capture the capillary wave induced pinch-off and daughter droplet ejection. We observe that on the porous structure the pinch-off is weak compared to that on a flat plate. Published by AIP Publishing.