Development of lattice Boltzmann method for complex multiphase flows

Development of an efficient lattice Boltzmann method for multiphase flows and phase change, which often occur while flows interact with structures in fluids engineering. This research will deliver a powerful tool for design, optimization, and management of coastal structures and renewable devices like oil platform and tidal or wave turbines.

When waves and storm approach to shorelines and coastal structures like sea defenses or breakwaters, waves break and may overtop the sea walls, generating complex air entrainment or multiphase flows. This could cause severe damage to structures and property along costs. Similar multiphase flows also widely exist during cavitation around water turbine for energy generator when local pressure falls below the critical pressure. Modelling and understanding of such multiphase flows become essential to design, optimise and manage costal structure and marine energy devices. Although there are many numerical methods available for modelling multiphase flows, e.g., one fluid approach, volume-of-fluid method, level-set method and front-tracking method, they often need special treatment for the free surface or interface like using shock-capturing scheme and marker cell method; and the associated simulation procedure is complicated and computationally inefficient, especially for modelling large-scale multiphase flows in practice. It is still challenging to develop an efficient and accurate model for multiphase flows and phase change. On the other hand, the lattice Boltzmann method (LBM) simulates fluid flows using simple algebraic calculations and has become a very successful and capable numerical method in the Computational Fluid Dynamics for capturing complex flows like those through porous media that still challenge competing numerical methods. It efficiently handles complicated boundary conditions and flows around multiple bodies. The computational code is easily parallelisable that can exploit large server and GPU architectures for extremely fast simulations. In the literature, the LBM has been applied to simulation of multiphase flows with certain success, but as a new approach, it is under investigation and needs further development. In this PhD project, we aim to develop a novel LBM to model multiphase flows for air entrainment as well as its associated phase change. The developed model will provide the key to understanding of wave breaking, wave overtopping, and cavitation, improving design of energy devices and maintenance/construction of coastal structures, especially under climate change.

Aim and Objectives:
Inherent efficiency and accuracy feature of the lattice Boltzmann method ensures that a highly efficient and accurate model for modelling complex flows can be achieved. As the LBM delivers a flexible and extensible computational framework for studying various complex flows, it is applied as the basis of developing a new multiphase flow model. Zhou (2004, 2007. 2008 & 2014) has already developed and extensively validated lattice Boltzmann methods for different flows with or without flow turbulence. This provides a PhD student with a solid foundation for further development of a powerful LBM to solve the complex multiphase flow equations. The overall objectives of the project are:
• To establish the new Navier-Stokes equations with suitable term for air entrainment and phase change,
• To develop a novel LBM to solve the new Navier-Stokes equations for multiphase flows,
• To improve the model to simulate the phase change to account for various degree of air entrainment in the multiphase hydrodynamics,
• To validate the model using the benchmark tests,
• To further develop the model by applying it to wave breaking, energy device and
• To improve the developed model through sensitivity and parameter study.
References
• Zhou, JG (2004) Lattice Boltzmann Methods for Shallow Water Flows. Springer-Verlag, Berlin.
• Zhou, JG (2007) A lattice Boltzmann model for groundwater flows. Int. J. Mod. Phys. C 18(6):973-991.
• Zhou, JG (2008) Axisymmetric lattice Boltzmann method. Phy. Rev. E 78(3):036701.
• Zhou, JG (2014) Lattice Boltzmann morphodynamic model. J. Comput. Phys. 270:255-264.