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

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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.