Speaker
Description
Moving contact lines in microchannels play a central role in many porous-media and microfluidic processes, yet they remain challenging to simulate accurately due to the stringent requirements on curvature and surface-tension evaluation near solid boundaries. We investigate contact-line dynamics in microchannels using direct numerical simulations within a volume-of-fluid (VOF) framework. To this end, we develop a height-function-based contact-angle enforcement method applicable to both flat and curved solid surfaces. The key idea is to incorporate the contact-line position into the curvature estimation in those cells containing the contact line, where the interface normal is constrained to the prescribed contact angle to ensure smooth contact-line motion.
On flat solid walls, the proposed model achieves higher accuracy than the conventional vertical height-function method for enforcing very small and very large contact angles [1]. The method also extends naturally to curved solid surfaces represented by the embedded boundary method, enabling the imposition of arbitrary contact angles while maintaining low levels of spurious currents in the vicinity of the contact line. A series of benchmark tests is used to demonstrate the accuracy and robustness of the method across a wide range of wettability conditions.
Building on this implementation, we study moving contact lines in microchannels with a range of geometries, including straight, sinusoidal, and multi-branch microchannels (Fig. 1, attachment). The relevant flows are characterized by small capillary number (Ca) and large Laplace number (La), which amplify the sensitivity of the solution to the curvature error near the contact line. We systematically analyze spurious currents—manifested as pressure and velocity oscillations within the channel (Fig. 2, attachment)—over wide ranges of capillary and Laplace numbers, with Ca down to $10^{-6}$ and La up to $10^{6}$. The results help clarify the mechanisms underlying the numerical contact-line pinning and other limitations of many existing contact-angle enforcement strategies [2-4]. Overall, these microchannel configurations provide a demanding set of benchmarks for assessing contact-angle models on embedded solid surfaces.
| References | [1] Afkhami, S., & Bussmann, M. (2008). Height functions for applying contact angles to 2D VOF simulations. International journal for numerical methods in fluids, 57(4), 453-472. [2] Tavares, M., Josserand, C., Limare, A., Lopez-Herrera, J. M., & Popinet, S. (2024). A coupled VOF/embedded boundary method to model two-phase flows on arbitrary solid surfaces. Computers & Fluids, 278, 106317. [3] Chen, X., Han, T., Pan, J., Fuster, D., & Zaleski, S. (2025). Volume-conserving method for dynamic contact line on complex surfaces. Physics of Fluids, 37(2). [4] Huang, C. S., Han, T. Y., Zhang, J., & Ni, M. J. (2025). A 2D sharp and conservative VOF method for modeling the contact line dynamics with hysteresis on complex boundary. Journal of Computational Physics, 533, 113975. |
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| Country | France |
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