3-D Direct Numerical Simulation of Gas–Liquid and Gas–Liquid–Solid Flow Systems Using the Level-Set and Immersed-Boundary Methods

The recent advances in level-set and Immersed Boundary methods (IBM) as applied to the simulation of complex multiphase flow systems are described. Two systems are considered. For system 1, a computational scheme is conceived to describe the three-dimensional (3-D) bubble dynamics in gas–liquid bubble columns and gas–liquid–solid fluidized beds. This scheme is utilized to simulate the motion of the gas, liquid, and solid phases, respectively, based on the level-set interface tracking method, the locally averaged time-dependent Navier–Stokes equations coupled with the Smagorinsky subgrid scale stress model, and the Lagrangian particle motion equations. For system 2, the hydrodynamics and heat-transfer phenomena of a liquid droplet in motion and during the impact process with a hot flat surface, as well as with a particle, are illustrated. The 3-D level-set method is used to portray the droplet surface deformation whilst in motion and during the impact process. The IBM is employed so that the particle–fluid boundary conditions are satisfied. The governing equations for the droplet and the surrounding gas phase are solved utilizing the finite volume method with the Arbitrary Lagrangian Eulerian (ALE) technique. To account for the multiscale effect due to lubrication-resistance induced by the vapor layer between the droplet and solid surface or solid particle formed by the film-boiling evaporation, a vapor-flow model is developed to calculate the pressure and velocity distributions along the vapor layer. The temperature fields in all phases and the local evaporation rate on the droplet surface are illustrated using a full-field heat-transfer model.