CBET-EPSRC: Droplet Impact on Fluid Interfaces: 3D Effects Across Scales

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This NSF-EPSRC project represents an integrated, comprehensive, and interdisciplinary investigation of droplets impacting onto liquid layers, with particular attention paid to three-dimensional effects that often arise in applications. Droplet-liquid impacts are fundamental to a range of industrial, agricultural, advanced manufacturing, environmental, and aerospace applications. As a droplet impinges on a liquid layer, several distinct outcomes are possible, which include complete rebound (bouncing), merging (deposition), and splashing. Depending on the target area of interest, each of these three distinct outcomes can be either desirable or undesirable. Broadening our current understanding of droplet impact phenomena to include three-dimensional effects is of critical and timely importance to unlocking and advancing real-world applications. This research program makes use of slow-motion photography and cutting-edge computer simulations. Collaborators at the University of Oxford and the University of Warwick will carry out the high-energy impact experiments and direct numerical simulations over all regimes of interest, respectively. Partners from the inkjet printing and aerospace industries are engaged in this project, ensuring a direct and accelerated track for knowledge transfer. The striking visual nature of droplet impact phenomena will also translate directly into the development of numerous outreach activities in collaboration with artists and graphic designers, with a target audience of young students from underrepresented and disadvantaged groups. The bulk of prior work on droplet-liquid and droplet-solid impact focuses on axisymmetric, normal impacts due to the relative simplicity of experimental characterization and visualization, and reduced computational demands. In practice, non-axisymmetric droplet-interface impacts are far more common. Recent advances in high-speed visualization, flow measurement techniques, multi-scale algorithms, and associated computing power will facilitate the proposed work plans and objectives. Studies in the present project include (i) normal impacts, with particular attention to the role of the interstitial gas layer, (ii) impacts onto a moving liquid layer, and (iii) oblique impacts. Each study focuses on delineating parametric thresholds between the impact regimes of rebound, coalescence, and splashing through a synthesis of experiments, high-fidelity numerical simulation, and reduced-order modeling and scaling analysis. The research outputs are anticipated not only to include the specific scientific discoveries, but also benchmarked and documented experimental and computational tools and datasets that will strengthen the broad global research efforts in the area, as well as a myriad of related topics including droplet-solid impacts, particle-liquid impacts, and droplet-droplet collisions. Having industrial partners involved in the project will ensure a streamlined pathway for the translation of the scientific advances towards real-world applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.