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

自由表面流动是工业流体力学中常见的现象。许多工业过程涉及复杂几何形状的几种流体的流动，因此涉及分离这些流体的界面的演变。此外，几何形状通常随时间而变化，这有时会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，溶解的空气就会成核，产生气泡。这种现象类似于沸腾。然后，流体的流动使气泡从低压区移动到高压区。然后，气泡可能在固体表面或固体表面附近剧烈地内爆。然后产生的射流似乎是造成空化侵蚀的原因，即一种由蒸汽气泡作用导致固体材料机械降解的侵蚀形式。腐蚀的材料使运动部件不像应有的那样有效，从而导致性能损失和重要的更换成本。由于外壳结构复杂，直接检测空化往往是不可能的。低马赫数空化流的数值模拟往往是水轮机设计人员唯一可用的工具。这个例子表明，自由表面流动的精确建模可以产生重大的经济和工业影响。本研究项目的主要目标是建立一个数值模型，以研究在工业应用中涉及移动边界的复杂多相流中发现的界面物理对自由表面动力学的影响。我们的研究计划的长期目标是为工程师提供一个通用的分析工具，负责涉及多相系统的工业过程的优化。

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.