Reports: G9
48631-G9 Numerical Modeling of Fluid Droplet Spreading and Contact Angle Hysteresis
The main objective of the proposed research is to use a combination of molecular dynamics and continuum methods and to investigate problems involving the moving contact line and slip boundary conditions, i.e., droplet spreading and contact angle hysteresis. During the reporting period (from 08/31/08 to 08/31/09) most of the efforts were focused on the development of the continuum and molecular dynamics numerical methods to simulate interfacial flows over smooth and corrugated surfaces. The student implemented the finite element method to solve two-dimensional Navier-Stokes equation for the flow over smooth and rough surfaces with slip boundary conditions. Some of the results were published in the Physics of Fluids (2009). This paper presents an interesting interplay between the local slip and inertia on the effective slip length and flow structure above periodically corrugated surfaces. In particular, it was found that an asymmetric vortex flow is developed in the grooves of the rough surface if the local slip is sufficiently small and the effective no-slip boundary plane is displaced into the fluid domain. On the other hand, if the local slip length is larger than the period of surface corrugation, then the vortex vanishes and the effective slip length increases. Thus, the results of the paper suggest a way to control of the flow transport (drug reduction) and flow structure (vorticity) by modifying surface wetting properties (slip boundary condition). In addition, the fluid-fluid interface and slip at the contact line were incorporated into the continuum code and test runs of the spreading process of the fluid droplet were performed. It was realized that the solution of the contact line problem is very sensitive to the grid resolution near liquid/solid interfaces. The size of each grid in the continuum simulation is chosen to be about two orders of magnitude smaller than the typical slip length. Finally, molecular dynamics simulations were also used to simulate two-phase flow with moving contact line over a smooth surface. Velocity fields, shear stresses, interface, and slip length were computed with high resolution and compared with the results reported in the literature. To conclude, Anoosheh Niavarani made a significant progress during the last year and she plans to graduate in the summer 2010. The results of the research (funded by PRF) will be very important in her search for the postdoctoral position.
