Brave new whorl: Vortex ring impingement on concave surfaces

Vortex ring interactions with solid and deformable surfaces abound in nature and engineering flows. This situation is particularly relevant to the problem of replacement speech following a laryngectomy, where unsteady flow exiting a tracheoesophageal prosthesis produces pulsatile vortex rings that impinge on the curved wall of the esophagus. The resultant esophageal pressure field is responsible for successfully producing tracheoesophageal (i.e., replacement) speech. As such, understanding the mechanics that arise as vortex rings impact curved surfaces, in particular the pressure loading that is produced, could lead to improved success rates of replacement speech. This work is also more broadly applicable to both biological and engineering flows, such as cardiac hemodynamics, fluidic energy harvesting, wall-bounded turbulence, etc. The physics of these interactions will be investigated via flow visualization and both two-dimensional and tomographic particle image velocimetry. Acquisition of the velocity fields will enable determination of vorticity topologies, pressure field estimation, and identification of pressure source terms, as well as the resultant wall loading that arises during these interactions. This proposal blends the research efforts with a novel outreach plan to help high-school choral students envision how an interest in artistic expression in voice can lead to a career in science and engineering. The proposed work plan will explore the mechanics of vortex ring-surface interactions with both hemispherical and cylindrical cavities. Flow visualization and particle image velocimetry will be utilized to explore how a primary vortex ring approaching a cavity induces flow on the surface of the cavity, and subsequently causes the flow to separate and roll-up into a secondary vortex ring, and potentially develop azimuthal instabilities. This interaction will be investigated in both axisymmetric (hemispherical) and two-dimensional cavity geometries as a function of cavity radius relative to the primary vortex ring radius. The pressure loading that develops on the concave surface will also be quantified to provide insight into the fluid-structure interaction. The outcomes from this research plan will improve success rates of tracheoesophageal speech. The project will also facilitate the training and education of one graduate and multiple undergraduate students. Finally, the outreach program will inspire high-school students to pursue careers in science and engineering fields, while also providing paid summer research experiences for two of them. 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.