Numerical modeling of complex interfacial physics for the simulation of industrial multifluid processes

自由表面流动在工业流体力学中是一种常见的现象。许多工业过程涉及几种流体在复杂几何形状中的流动，因此分离这些流体的界面的演变。此外，常见的是几何形状随时间演变，这有时以非常复杂的方式影响自由表面的动力学。例如，水轮机设计者必须考虑空化现象。当水与高速运动的转轮叶片接触时，局部受到压降的影响。溶解的空气成核形成气泡。这种现象类似于沸腾。当流体流动时，气泡会从低压区域移动到较高压力的区域。然后气泡可能会在固体表面上或接近固体表面剧烈内爆。然后产生一股似乎是空蚀的原因，即通过蒸汽气泡的作用导致固体材料机械降解的一种侵蚀形式。被侵蚀的材料使移动的部件不能达到应有的效果，这会导致性能损失和重要的更换成本。由于外壳的复杂结构，通常不可能直接检测到空化。低马赫数空化流动的数值模拟通常是水轮机设计人员可用的唯一工具。这个例子表明，自由表面流动的准确建模可以产生重大的经济和工业影响。该研究项目的主要目标是开发一个数值模型，研究界面物理对工业应用中涉及移动边界的复杂多相流中自由表面动力学的影响。我们研究计划的长期目标是为负责涉及多相系统的工业过程优化的工程师提供一个通用的分析工具。

Free surface flows are a common occurrence in industrial fluid mechanics.  Many industrial processes involve the flow of several fluids in complex geometries, and therefore the evolution of the interfaces separating these fluids.  Moreover, it is common to have geometries evolving with time, which influence, sometimes in a very complex way, the dynamics of free surfaces.  For example, hydraulic turbine designers have to take into account the cavitation phenomenon.  When water, in contact with runner blades moving at high velocity, is locally submitted to a pressure drop, the dissolved air nucleates to create bubbles.  This phenomenon is similar to boiling.  The fluid flow then makes the bubbles move from low pressure to higher pressure regions.  The bubbles may then violently implode on or close to a solid surface.  A jet is then created which seems to be the cause for cavitation erosion, i.e. a form of erosion responsible for the mechanical degradation of solid materials by the action of vapor bubbles.  The eroded materials make the moving components not as effective as they should be, which leads to performance loss and important replacement costs.  Direct detection of cavitation is often impossible due to the complicated structure of the enclosure.  The numerical simulation of low Mach number cavitation flows is often the only tool available to hydraulic turbine designers.  This example shows that the accurate modeling of free surface flows can have a significant economical and industrial impact. The main objective of this research project is to develop a numerical model to study the influence of interfacial physics on the dynamics of free surfaces found in complex multiphase flows involving moving boundaries, that are found in industrial applications.  The long term goal of our research program is to provide a general analysis tool for engineers in charge of the optimization of industrial processes involving multiphase systems.