A Lattice Boltzmann based Single-Phase Model: Surface Tension and Wetting Xiu Qing Xing, David Lee Butler, and Chun Yang School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, 639798 xqxing@ntu.edu.sg Summary. A 2D single-phase free surface tracking model using the Lattice Boltz- mann method (LBM) is developed in this study. In contrast to the conventional multi-phase models, it is not necessary to simulate the motion of the gas phase using this LBM single-phase algorithm, and thus improves the computational effi- ciency without sacrificing the underlying physics. Based on Gunstensen ′ s immiscible Lattice Boltzmann algorithm, a perturbation is added to the distribution functions of the interface cells for introducing the surface tension and wetting into the LBM single-phase model. Implementations of the model are demonstrated for simulations of droplet deformation under the surface tension effect and the droplet spreading on solid surface with various wetting properties. Simulation results show that the pro- posed model can generate a surface tension that is isotropic, and the model allows for continuous control of contact angles by varying the mass gradient at the wall boundary cells. 1 Introduction The simulation of flows with free surfaces has a variety of technical appli- cations such as flow through porous media, boiling dynamics and etching processes. Difficulties in the simulation of these types of problems lie in mod- eling interface dynamics and dealing with the complex boundaries. Several LBM models to simulate the interfacial dynamics have been developed in the past decade. Gunstensen et al.[1] proposed a color model for simulating im- miscible binary fluids based on Lattice Gas model of Rothman and Keller[2]. D ′ Ortona et al.[3] studied the surface tension and wetting properties by mod- ifying the color redistribution step and obtained good agreement with theory. Shan and Chen[4, 5] and Shan and Doolen[6] considered a fluid with S differ- ent components on a regular lattice. In order to include the surface tension, they modified the collision operator by adding the force on the kth phase ow- ing to a pairwise interaction between different phases. Orlandini et al.[7] and Swift et al.[8, 9] proposed a free energy approach for simulating binary fluids and liquid-gas fluids. The surface tension is considered by incorporating a free H. Deconinck, E. Dick (eds.), Computational Fluid Dynamics 2006, DOI 10.1007/978-3-540-92779-2 97, c  Springer-Verlag Berlin Heidelberg 2009