Cavitation consists of the formation, growth, and implosion of bubbles in a liquid when exposed to rapid pressure drop. The final step of the bubble implosion consists of a rapid compression of the internal gases, much faster than the thermal exchanges, which results in high amplitude pressure pulses that cause some damage on nearby solid surfaces. This project focuses on the small-scale mechanisms of this process, called cavitation erosion. More specifically, it is intended to characterize the complex interaction between the fluid and the material response, and to clarify the primary causes of the impacts experienced by a material located close to bubble collapses. For that purpose, joint numerical and experimental works will be performed: (i) A novel and advanced multiphysics computational framework capable of predicting the dynamic interaction of collapsing cavitation bubbles with a nearby deformable material will be developed, (ii) Experiments combining the imaging of the bubble evolution with measurements of the velocity and temperature fields in the liquid, and local efforts on the solid surface will be conducted. Both approaches will focus on the collapse of a single bubble near the material surface. Completion of this project will potentially lead to controllable cavitation bubble collapse, which is a major challenge for the optimization of various medical and industrial processes. The project will also enable teaching the cross-disciplinary science of cavitation to both ocean and biomedical engineers; and to engage K-12 students to learn about the interesting phenomenon of cavitation and its broader impacts.
The bubble-material interaction problem related to the collapse of cavitation bubbles close to a solid surface is a challenging multiphysics and multiscale problem involving a strong coupling between the fluid dynamics and the wall deformation. The dynamic process is highly nonlinear, featuring shock waves, high speed flows, large deformation and topological change of liquid-gas interface, and shock-induced fracture. The effects of the bubble size, distance to the wall and characteristic time of the collapse on the effects on the wall are currently an open question. More specifically, the respective impacts of the microjet and the shock waves, according to these different parameters, in terms of local efforts, elastic or plastic deformation, and potential mass loss have to be clarified. Both the effects of a single bubble collapse and the cumulative effects of the collapses are of interest, to eventually determine the primary mechanisms that are responsible for the damages. In the present project, this problem is investigated by a joint numerical and experimental approach. The computational framework will incorporate high-fidelity models to capture the propagation of shock waves across material interfaces, large deformation of bubbles and solid materials, and shock-induced material failure. After validation, it will enable, for the first time, to explicitly and quantitatively explore the two-way fluid-solid coupling, that is, both (i) the stress, deformation, and failure of the solid material induced by the pulsatile high velocities, pressures, and temperatures resulting from bubble collapse; and (ii) the reciprocal impact of the acoustic and elastic properties of the solid material to the shock-dominated two-phase fluid flow. The experiments will use high speed optical and X-ray imaging, cold wires for high frequency temperature measurements, and innovative array sensor based on PVDF (polyvinylidene fluoride) coating for local effort measurement.
