Научные семинары лаборатории 3 июля
3 июля прошли два очередных научных семинара Международной лаборатории суперкомпьютерного атомистического моделирования и многомасштабного анализа. С двумя докладами на тему "Slip Behavior in Liquid Films: Influence of Patterned Surface Energy, Flow Orientation, and Deformable Gas-Liquid Interface" выступил главный научный сотудник лаборатории, профессор Wright State University (США) Приезжев Николай Вячеславович.
1) Abstract: The influence of periodic and random surface textures on the flow structure and effective slip length in Newtonian fluids is investigated by molecular dynamics (MD) simulations. This study is motivated by the possibility to generate transverse flows in microfluidics devices to enhance mixing and separation processes. We consider a situation where the typical pattern size is smaller than the channel height and the local boundary conditions at wetting and nonwetting regions are characterized by finite slip lengths. We first report on a detailed comparison between continuum and MD simulations of a liquid film subject to planar shear in a Couette cell. It will be shown that at low shear rates there is excellent agreement between the velocity profiles and the effective slip lengths when the characteristic length scale of substrate inhomogeneities is larger than approximately 30 molecular diameters. We conclude this part by a discussion of the molecular aspects which cause deviations from hydrodynamic predictions at smaller length scales.
2) Abstract: In case of flows over anisotropic textures, the interfacial diffusion coefficient of fluid molecules near heterogeneous surfaces correlates well with the effective slip length as a function of the shear flow direction with respect to the texture orientation. In addition, it was found that the angular dependence of the effective slip length obtained from MD simulations is in good agreement with hydrodynamic predictions provided that the pattern size is larger than several molecular diameters. These findings lend support for the microscopic justification of recently introduced tensor formulation of the effective slip boundary conditions in the case of noninertial flows of Newtonian fluids over smooth surfaces with nanoscale anisotropic textures. Finally, we briefly discuss recent numerical results for slip flows over smooth surfaces with flattened gas bubbles trapped by regions of different wettability. In particular, it will be shown that the spatial distribution of the local slip length becomes asymmetric due to shear-induced deformation of the attached bubble. The results from the last part of presentation are obtained in collaboration with the group of Prof. Hu from Northwestern Polytechnical University, China.