Taehun Lee, Ph.D. - US grants

The objective of the proposed research is to develop an unstructured lattice Boltzmann method (LBM) based on the Galerkin formulation (GLBM) for the direct simulation of liquid slip on superhydrophobic surfaces and identify important design factors that maximize the effective slip under practical conditions. The large effective slip on superhydrophobic surfaces is expected due to the sizable difference in viscosity between liquid and gas that is trapped in the nanostructures. A successful numerical model should be able to deal with complex shape of superhydrophobic surfaces and large viscosity difference between fluids. The proposed two-phase GLBM on the unstructured mesh will overcome several undesirable properties inherent to the LBM on the structured mesh as a modeling tool for superhydrophobic surfaces; namely, instability at large density/viscosity difference and geometrical restriction imposed by the mesh. It will enable investigation of detailed flow physics on superhydrophobic surfaces covered with complex nanostructures. The proposed research is to: (1) Develop GLBM for immiscible two phase flows having a large density and viscosity ratio, using implicit time marching on unstructured mesh; (2) Establish appropriate boundary conditions at the liquid-solid-gas boundary based on the minimization of the free energy and incorporate them into GLBM framework; (3) Examine the physics of continuous and dispersed (droplets) liquid flows on superhydrophobic surfaces with complex nanostructures; and (4) Find the optimum profile and distribution of nanostructures for the maximum superhydrophobicity and effective slip.

Superhydrophobic surfaces are of great interest in many industrial and biological applications, because properties such as anti-sticking, anti-contamination, and self-cleaning are expected. When a droplet rolls over a contamination, it collects the particles from the surface and the contaminant particles are removed from the surface. In microfluidic and biomedical applications, superhydrophobic surfaces reduce the hydrodynamic drag at the wall, and prevent cross-contamination of one drop by another one moving on the same surface. The proposed research explores a new modeling capability that could significantly change existing approaches to designing microfluidic devices and help prescreen design alternatives reducing the design cost. The research experience acquired from the proposed project will also enhance the course materials for the advanced computational fluid dynamics courses.

The proposal seeks funds to partially cover travel expenses of graduate students, post-doctoral researchers, and junior faculty members from institutions in the United States to participate in the International Conference for Mesoscopic Methods in Engineering and Science (ICMMES) that will be held July 14-18, 2014 at CUNY in New York City. The main intellectual merit of this conference lies in the exchange of scientific ideas, presentations of cutting edge research, and exposure to a richly diverse array of topics in the area of mesoscopic of fluid dynamics. The conference organization is in direct response to the growing interest in multi-scale and multi-physics phenomena observed in nano- or micro-systems and biological systems, and the increasing importance of computational science to research in these disciplines. The conference will be attended by both prominent and young scientists in fluid dynamics from around the world.
Topics for the ICMMES conference series include modeling and numerical schemes based on mesoscopic and kinetic methods and their analysis and applications to areas that include (i) Computational fluid dynamics (CFD), including direct numerical simulations (DNS), large-eddy simulations (LES), and turbulence modeling;(ii) Rheology for complex fluids and soft matter such as bio-fluids, suspensions, multi-phase and multi-component fluids, non-Newtonian fluids, and electro-rheological (ER) and magnetorheological (MR) fluids (smart fluids);(iii) Nano-scale phenomena involving non-continuum, surface-dominated, low-Reynolds-number, (iv) non-Newtonian, multi-scale and multi-physics effects. Examples are complex flows through porous media, gaseous flows in micro-devices, electrokinetic-capillary phenomena and droplets and bubbles in micro-fluidics; (v) Computational methods for multi-scale and multi-physics such as (turbulent) flow-structure interactions and thermo-chemically nonequilibrium flows, reactive flows and combustion, and radiation heat transfer; (vi) Algorithms for parallel high performance computing (PHPC) with engineering applications;(vii) Special computer hardware (e.g., general purpose graphic processing units or GPGPUs).

The conference will foster cross-fertilization of ideas among researchers and will address challenges involved in advancing the field in the near future. The financial support will be used to increase participation of US students and young scientists who would not otherwise be able to afford to travel to the meeting and pay associated costs. Special consideration will be given to under-represented minorities, women, persons with disabilities, and those in Historically Black Colleges and Universities (HBCU) and Hispanic Serving Institutions (HSIi).