GOALI: Fundamental Studies on High Impact Pressure, Supersonic Water Droplets for Material Deformation and Removal

超高压、高速连续水柱用于许多应用中，例如，在金属的水射流切割中作为磨料的载体。在理想条件下，射流的水压等于泵产生的压头。 然而，过去的研究表明，水流破碎成液滴产生的冲击压力大大超过了水锤压力。这个学术联络与工业（GOALI）奖资助机会支持液滴形成和液滴表面相互作用现象的基础研究。这项研究的结果可以帮助实现他们的应用，从喷丸到涂层去除，以更经济和环保的方式加工。这将使整个社会受益，因为与竞争技术相比，这将创造出用水量和污染材料显著减少的环境友好型工艺。 本研究的目的是（1）评估各种工艺参数的影响，即，并流气体速度、室分压、高频不稳定性触发、以及液滴形成时的降低的韦伯数;（2）确定液滴特性，即，液滴速度、直径和间距，这是产生所需液滴-表面相互作用结果所需的（例如，残余应力、表面粗糙度或材料去除速率）;（3）表征高变形速率下的材料行为和三轴应力破坏机制;以及（4）实现可以处理大表面积的多射流系统并研究附加的工艺参数，即，喷射间距和单个喷射压力。本研究将使用的工具是：（i）实验装置，包括测量关键工艺参数，即，上述可视化液滴特性、液滴力和温度;以及（ii）一套捕获液滴-表面相互作用结果的预测有限元模型。 所使用的方法将是实验性的（允许控制、测量和探索工艺参数）和具有验证模型的数值（与简单的试错实验方法相比，允许进一步研究设计空间）。从这项研究中获得的知识也将有益于其他物理现象的研究，例如，空蚀学术，工业和国家实验室合作伙伴在流体动力学和固体力学建模，实验方法，材料表征，机器开发和制造方面具有重要的专业知识，以确保这项研究的成功。

Ultra high pressure, high velocity continuous columns of water jets are used in a number of applications, e.g., as a carrier for grit in water jet cutting of metals. Under ideal conditions, the water pressure of the jet is equal to the pressure head generated by the pump. However, past research has shown that the breakup of the stream into droplets produces impact pressures that significantly exceed the water-hammer pressure. This Grant Opportunity for Academic Liaison with Industry (GOALI) award supports fundamental research into droplet formation and droplet-surface interaction phenomena. Results from this research can help achieve their applications from peening to coating removal to machining in a more economical and environmentally friendly manner. This will benefit society at large by creating environmentally friendly processes with significantly less water usage and contaminated materials compared to competing technologies. Objectives of this research are to (1) assess the effect of various process parameters, i.e., co-flow gas velocity, partial chamber pressure, high frequency instability triggering, and reduced Weber number on droplet formation; (2) determine the droplet characteristics, i.e., droplet velocity, diameter, and spacing, that are required to create the desired droplet-surface interaction results (e.g., residual stresses, surface roughness, or material removal rate); (3) characterize the material behavior and triaxial stress failure mechanisms at high deformation rates; and (4) implement a multi-jet system that can process large surface areas and study additional process parameters, i.e., jet spacing and individual jet pressure. The tools that will be used in this research are (i) an experimental set-up which includes measurement of key process parameters, i.e., visualized droplet characteristics listed above, droplet force, and temperature; and (ii) a suite of predictive finite element models that capture the droplet-surface interaction results. The methodologies used will be both experimental (to allow process parameters to be controlled, measured, and explored) and numerical with validated models (to allow further investigation of the design space compared to simply a trial-and-error experimental approach). The knowledge gained from this research will also benefit the study of other physical phenomena, e.g., cavitation erosion. The academic, industrial, and national laboratory partners have significant expertise in fluid dynamics and solid mechanics modeling, experimental methods, material characterization, machine development, and manufacturing, pertinent to assuring the success of this research.