Inertial jets from cavity collapse & granular impact

University Of Chicago, Chicago IL

Investigators

Abstract

The theoretical/simulational research focuses on liquid and granular jets that impact at a free surface. For liquid flow, the research will examine the jet formed upon collapse of a cavity. The work will focus on the generic situation where the dynamics is not axisymmetric but instead fully three-dimensional. For granular flow, the research will focus on the ejecta sheet formed when a densely packed granular jet collides with a solid target. Intellectual Merit: In both problems, numerous small-scale deviations are present in the initial state giving rise to jetting. In jetting from a collapsing cavity, recent studies revealed that the shape of the interface which first forms into a jet is generically fully three-dimensional, characterized by strong azimuthal distortions. In granular impact, each non-cohesive grain in the jet collides with the target and introduces a small disturbance to the mean motion. Intuitively one would expect that these deviations would prevent jetting and create a disordered response. The strongly distorted cavity should break up into a shower of air bubbles instead of forming a strong central jet. The granular jet, upon colliding with the target, should break up into a diffuse spray instead of forming a thin ejecta sheet with a well-defined ejection angle. The counter-intuitive outcomes in both cases connect them to a central puzzle in fluid dynamics. Under some circumstances, strong forcing appears to act in such a way as to organize the dynamics, producing a coherent structure (a central jet or a thin ejecta sheet) out of a disordered background. Insights from research into these two particular examples, which are novel, conceptually simple, and experimentally accessible can potentially transform our understanding of wide class of phenomena. Broader Impacts: Collapse-induced jets are believed to cause erosion of turbines in submarines, failure in steam turbines as well as wave-damage on shore breaks. Spray and atomization technologies rely on the formation of thin, fast moving jets that break-up into many droplets. Microfluidic devices that rely on collapse-induced jets to cleave bubbles with precision are being developed. Snow avalanches, or rock falls, propagating at high speeds can end up ejecting a great deal of materials upwards when they encounter an obstacle. On a slower scale, the craters formed by raindrop impact in a heavy downpour can be an important mechanism for soil erosion. Finally, many drugs and food products are processed as streams of particles. The proposed research also provides an excellent education for graduate students. It combines close collaboration between theory and experiment. Undergraduates will be recruited to work on both the experimental and simulation aspects of the project as part of the University of Chicago?s Research Experience for Undergraduates (REU) program. Results from the research will also be incorporated into the curriculum of two elective courses (one undergraduate / one graduate) that the PI has developed.