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A wetting boundary condition for handling contact line dynamics on three-dimensional curved geometries is developed in the lattice Boltzmann color-gradient framework. By combining the geometrical formation and the prediction-correction wetting scheme, the present wetting boundary condition is able to avoid the necessity to select an appropriate interface normal vector from its multiple solutions in the previous prediction-correction method. The effectiveness and accuracy of the wetting boundary condition are first validated by several benchmark cases, namely a droplet resting on a flat surface and on a solid sphere, and the spontaneous imbibition into a cylindrical tube. We then use the color-gradient model equipped with the developed wetting boundary condition to study the trapping behavior of a confined droplet in a microchannel with a cylindrical hole on the top surface, in which the effects of the hole radius and the droplet radius are identified for varying capillary numbers. Results show that the simulated critical capillary numbers, below which the droplet would be anchored by the hole, and the steady-state shapes of the anchored droplet generally match well with their theoretical solutions. The critical capillary number is found to decrease by either decreasing the hole radius or increasing the droplet radius, which is attributed to the weakened anchoring surface energy gradient and the enhanced driving force from outer flow, respectively. In addition, we show that the previous theoretical solutions are valid only when the initial droplet radius is greater than twice the height of the channel.
A wetting boundary condition for handling contact line dynamics on three-dimensional curved geometries is developed in the lattice Boltzmann color-gradient framework. By combining the geometrical formation and the prediction-correction wetting scheme, the present wetting boundary condition is able to avoid the necessity to select an appropriate interface normal vector from its multiple solutions in the previous prediction-correction method. The effectiveness and accuracy of the wetting boundary condition are first validated by several benchmark cases, namely a droplet resting on a flat surface and on a solid sphere, and the spontaneous imbibition into a cylindrical tube. We then use the color-gradient model equipped with the developed wetting boundary condition to study the trapping behavior of a confined droplet in a microchannel with a cylindrical hole on the top surface, in which the effects of the hole radius and the droplet radius are identified for varying capillary numbers. Results show that the simulated critical capillary numbers, below which the droplet would be anchored by the hole, and the steady-state shapes of the anchored droplet generally match well with their theoretical solutions. The critical capillary number is found to decrease by either decreasing the hole radius or increasing the droplet radius, which is attributed to the weakened anchoring surface energy gradient and the enhanced driving force from outer flow, respectively. In addition, we show that the previous theoretical solutions are valid only when the initial droplet radius is greater than twice the height of the channel.
An unconventional model of three-phase contact liny dynamics is suggested for the numerical solution of the boundary value problem of dipping and spreading. The numerical modeling is conducted with the use of the finite-element method in Lagrange variables. The mathematical model of the process is described by the equation of motion, continuity, and natural boundary conditions on the free surface. To exclude the ity of viscous stresses in the mathematical model on three-phase contact lines (TPCL) there was suggested a gridded model of gliding that takes into consideration peculiarities of dissipative processes in the neighborhood of TPCL at the microlevel. To reduce oscillations of pressure in the neighborhood of TPCL, a finite element is used. The suggested method allows for natural monitoring of free surface and TPCL with an unconventional model for dynamic contact micro-angle. A stable convergent algorithm is suggested that is not dependent on the grid step size and that is tested through the example of a three-dimensional semispherical drop and a drop in the form of a cube. The investigations obtained are compared to well-known experimental and analytical results demonstrating a high efficiency of the suggested model of TPCL dynamics at small values of capillary number.
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