THERMAL LATTICE BOLTZMANN TWO-PHASE FLOW MODEL FOR FLUID DYNAMICS

This dissertation presents a systematic development of a new thermal lattice Boltzmann multiphase model. Unlike conventional CFD methods, the lattice Boltzmann equation (LBE) method is based on microscopic models and mesoscopic kinetic equations in which the collective behavior of the particles in a system is used to simulate the continuum mechanics of the system. Due to this kinetic nature, the LBE method has been found to be particularly useful in applications involving interfacial dynamics and complex boundaries, e.g. multiphase or multicomponent flows. First, the methodology and general concepts of the LBE method are introduced. Following this introduction, an accurate mass conserving wall boundary condition for the LBE method is proposed together with benchmark test results. Next, the widely used Shan and Chen (SC) single component two-phase flow model is presented, as well as improvements to that model. In this model, by incorporating fluid-fluid interaction, phase separation and interfacial dynamics can be properly captured. Sharp interfaces between phases can be easily obtained without any additional numerical treatment. In order to achieve flexibility for the surface tension term, an additional force term which represents the contribution of surface tension is incorporated into the fluid-fluid interaction force term. The validity of this treatment is verified by our simulation results. Different equations of state are also incorporated into this model to compare their behavior. Finally, based on the SC model, a new and generalized lattice Boltzmann model for simulating thermal two-phase flow is described. In this model, the SC model is used to simulate the fluid dynamics. The temperature field is simulated using the passive-scalar approach, i.e. through modeling the density field of an extra component, which evolves according to the advection-diffusion equation. By coupling the fluid dynamics and temperature field through a suitably defined body force term, the thermal two-phase lattice Boltzmann model is obtained. Our simulation results show that different equations of state, variable wettability, gravity and buoyancy effects, and relatively high Rayleigh numbers can be readily simulated by this new model. Lastly, the accomplishments of this study are summarized and future perspectives are provided