Modelling of multiphase and multicomponent flows at high-density and high-viscosity contrasts by Lattice Boltzmann methods1

Abstract

Numerical modelling of multiphase flows remains a challenging subject in fluid mechanics. Multiphase and multicomponent flows are predominant in nature. Such applications are like melting ice and freezing water into ice cubes. And boiling and the formation of snow into the clouds are popular examples routinely experienced in daily life. Interestingly, phase transi- tions play an important role in several industrial areas. Common applications involve cooling devices, ranging from medicine/vaccine storage to fresh product transportation and the de- sign of battery thermal management systems for electric vehicles. Especially, the design of battery thermal management systems for electric vehicles is a challenging problem involv- ing phase change materials. To develop and validate Computational Fluid Dynamics(CFD) model for studying such problems in the industry is needed. A deep understanding of the laws governing phase transitions may significantly improve the design process of such industrial systems. The main goals are to understand the physics of multiphase and multicomponent fluids. The physical domain is a container filled by two fluids; namely heavy fluid and light fluid, such as air and liquid. computational domain is meshed by an uniform fine grid. The computational domain is defined by an equidistant fine grid. This can be attained without a significant loss of computational performance since Lattice Boltzmann Methods (LBM) require much less memory and CPU time than conventional finite volume, finite difference methods. The purpose of this present research project is to investigate the multiphase and multicom- ponent fluids flow at high density and high viscosity ratios. The numerical simulation used by the phase-field-based Lattice Boltzmann model(LBM). Heavy fluid and lighter fluid are considered such are water and air. Interface tracking methods for multi-component fluids are analysed by the Central moments (CMs) method. Analysis of the evolution at the interface with various time instants has been observed through several test cases. Two sets of equations are considered which are the Navier-Stokes equations and Allen–Cahn equation [1][2] . Allan-Chan equation(conservative form) is used to track the interface of the two fluids. Finally, phase-field-based LBM is discussed in the result section. Rayleigh Taylor instability is the phenomena of instability analysis between two different density flu- ids that occur at the interface of the two fluids. Examples of Rayleigh Taylor instability are the behaviour of oil suspended above water in the gravity of Earth. Rayleigh-Taylor instability analysis shows that the Allen-Cahn equation can be correctly recovered by this model successfully with second-order accuracy [3]. The result shows a broad range of behaviours of the interface, that depends on the Reynolds number, and Atwood number. In particular, the emergence of saddle point or fluid tip, droplet and later mixing part in which Kelvin Helmholtz(KH) instability takes place. Kelvin Helmholtz instability is used in the fluid dynamics field to understand turbulent phenomena of the two different fluid’s behaviour. Where turbulent phenomena is the chaotic mixing of the two fluids. Furthermore, this behaviour is associated with the Rayleigh Taylor instability with lower and higher Reynolds number fluid flow interface at the initial stage to intermediate stage of the simulation.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Alistair Revell (Supervisor)