(297c) An Adaptive Lattice Boltzmann Method and Its Application in Multiphase Flows

The lattice Boltzmann method (LBM) is a versatile and efficient numerical technique for simulating multiphase flows. A number of LBM approaches have been developed for flows with gas bubbles or liquid droplets. However, many such simulations face the problem of inaccurate presentation of the boundary between two phases, and numerical instability when simulating low-viscosity fluids. As the result, those LBM simulations are often limited to slightly deformed droplet or bubbles and low Reynolds number flows. This study presents a new LBM technique that is able to accurately capture the deformation of the interface, and remain stable for Reynolds number up to O(10^3). The approach is based on the improved interaction potential model, in which the two phases spontaneously segregate due to the interacting force. The adaptive mesh refinement (AMR) is used to improve the grid resolution near the interface while maintaining the total grid number manageable. At the same time, the multiple-relaxation-time (MRT) algorithm is used to enhance numerical stability at high Reynolds numbers and to reduce spurious velocity near the interface. The principle and validation of the AMR and MRT algorithms will be briefly discussed. Numerical examples will be given first for buoyant rise of bubbles under various conditions. Particularly, ellipsoidal cap and skirted bubble with large deformation, and millimeter sized bubbles in water with high Reynolds number can be simulated by this new LBM technique. Then simulation of droplet formation process in microfluidic applications will also be discussed to demonstrate the capability of the method in treating complicated topological changes of the interface.