A random projection method for sharp phase boundaries in lattice Boltzmann simulations

Existing lattice Boltzmann models that have been designed to recover a macroscopic description of immiscible liquids are only able to make predictions that are quantitatively correct when the interface that exists between the fluids is smeared over several nodal points. Attempts to minimise the thickness of this interface generally leads to a phenomenon known as lattice pinning, the precise cause of which is not well understood. This spurious behaviour is remarkably similar to that associated with the numerical simulation of hyperbolic partial differential equations coupled with a stiff source term. Inspired by the seminal work in this field, we derive a lattice Boltzmann implementation of a model equation used to investigate such peculiarities. This implementation is extended to different spacial discretisations in one and two dimensions. We shown that the inclusion of a quasi-random threshold dramatically delays the onset of pinning and facetting

Tracking single bubble in Hall-Héroult aluminium cell : an experimental and numerical study

In simulations of the hydrodynamics of the multiphase flow in gas– liquid systems with finite sizes of bubbles, the important thing is to compute explicitly the time evolution of the gas–liquid interface in many engineering applications. The most commonly used methods representing this approach are: the volume of fluid and the phase field methods. The later has gained significant interest because of its capability of performing numerical computations on a fixed Cartesian grid without having to parametrise these objects (Eulerian approach) and at the same time it allows to follow the interface ( for example bubble’s shape) that change the topology. In this paper, both numerical (phase field method) and experimental results for the bubble shapes underneath a downward facing plane is presented. Experiments are carried out to see the bubble sliding motion underneath a horizontal and inclined anode. It is assumed that the bubble formed under the anode surface is deformed (flattened) due to buoyant field before it goes around the anode corner. The bubble elongates to form a tail-like shape. The change in shape of the bubble is almost instantaneous and has a significant effect on the localised hydrodynamics around the bubble, which could influence the dynamics of the flow patterns in the Hall–Héroult cell. This deformation is the main cause of the bubble wake and the induced flow field in the aluminium cell. Various parameters such as bubble size, deformation and its sliding mechanism at different surface tensions are discussed and compared with experimental results

Study on Basic Rules of Noncontact Rod-induced Electrospinning

纳米纤维由于其超高的比表面积和卓越的力学、电学和化学特性在传感、生物医药、能源等领域有着广泛的应用前景和强劲的市场需求。静电纺丝是目前批量化制备纳米纤维的最重要方法之一，针对现有电纺方法存在的如多针尖多管孔电纺技术射流间相互影响，针尖管孔易堵塞；依靠特殊形状电极以及液面扰动的自由液面电纺则存在电极钝化和纤维形貌差异大等缺点，论文提出非接触式棒诱导电纺方法：采用接地诱导棒在聚合物液面近空间移动，强电场作用下靠近诱导棒的液面上出现大量微细射流，诱导棒移开后射流经过拉伸、鞭动和挥发，在接地收集板上收集到大量纳米纤维。论文围绕非接触诱导电纺基本工艺规律、流体运动机理与行为分析以及非接触诱导电纺装备开发...Because of its high surface area and excellent mechanical properties, nanofibers can be widely used in the fields of sensors, biomedicine, energy and so on. Electrospinning is one of the most important methods for manufacturing nanofibers, while there are some difficulties for electrospinning in mass production. For multi-nozzle or multi-hole electrospinning, adjacent jets show interference with e...学位：工学硕士院系专业：航空航天学院_飞行器设计学号：3202014115284

Assessment of an energy-based surface tension model for simulation of two-phase flows using second-order phase field methods

Second-order phase field models have emerged as an attractive option for capturing the advection of interfaces in two-phase flows. Prior to these, state-of-the-art models based on the Cahn-Hilliard equation, which is a fourth-order equation, allowed for the derivation of surface tension models through thermodynamic arguments. In contrast, the second-order phase field models do not follow a known energy law, and deriving a surface tension term for these models using thermodynamic arguments is not straightforward. In this work, we justify that the energy-based surface tension model from the Cahn-Hilliard context can be adopted for second-order phase field models as well and assess its performance. We test the surface tension model on three different second-order phase field equations; the conservative diffuse interface model of Chiu and Lin [1], and two models based on the modified Allen-Cahn equation introduced by Sun and Beckermann [2]. Additionally, we draw the connection between the energy-based model with a localized variation of the continuum surface force (CSF) model. Using canonical tests, we illustrate the lower magnitude of spurious currents, better accuracy, and superior convergence properties of the energy-based surface tension model compared to the CSF model, which is a popular choice used in conjunction with second-order phase field methods, and the localized CSF model. Importantly, in terms of computational expense and parallel efficiency, the energy-based model incurs no penalty compared to the CSF models.Comment: 13 pages, 5 figures, Revision submitted to Journal of Computational Physic