A coupled lattice Boltzmann/finite volume method for turbulent gas-liquid bubbly flows

Abstract

The study of gas-liquid multiphase flows has been an active research topic for many decades. They occur in processes belonging to industries including chemical, pharmaceutical, food, energy, and machinery industries. As processes in these fields become more refined, there is an increasing demand for the detailed analysis and accurate prediction of such flows. There are many categories of multiphase gas-liquid flows. We consider a dispersed phase in a carrier phase, such as small gas bubbles in liquids or liquid droplets in a gas. The technical application is a pulsed electrochemical machining (PECM) process, in which gas bubbles are generated in a liquid electrolyte during the electrochemical removal of material. The simulation method is based on an Eulerian-Eulerian model for the dispersed gas-liquid bubbly flow. The conservation equations are volumetrically averaged, resulting in one set of conservation equations per phase. The liquid phase is using a Lattice-Boltzmann method, while the gas phase is modelled by a Finite-Volume method. Interface terms between the phases result in a two-way coupled system. Both methods are formulated on a shared Cartesian grid similar to the concept in [1], which facilitates the exchange of information between the two solvers and an efficient implementation on HPC hardware. This coupled multiphase approach combines the advantages of the Lattice Boltzmann method as an efficient prediction tool for low Mach number flows with those of a finite-volume method for the Navier-Stokes equation used for the phase with larger density changes. To accurately model the turbulent motion of the liquid phase on all relevant scales, a cumulant-based collision step for the Lattice-Boltzmann scheme [2] is combined with a Smagorinsky sub-grid-scale turbulence model. In the finite-volume solver, the effects of the sub-grid-scale turbulence are incorporated according to the MILES approach. For the validation of the new method, large-eddy simulations (LES) of turbulent bubbly flows are performed. The accuracy of the predictions is evaluated comparing the results to reference data from experiments and other simulations for generic test cases, for which good agreement is found. The applicability of the method will be demonstrated for a bubbly turbulent channel flow, which mimics the phenomena in the PECM process.