A key hydrodynamic feature of vortex ring formation with implication to propulsion is that there is a limit in ring growth. Studies have established the limiting process on isolated vortex ring formation from a starting jet, and associated optimal ring formation with the limiting formation time. Inspired by animals such as squids and medusae, a novel propulsion technique has been developed utilizing consecutive vortex rings generated from a pulsed jet. The ring formation process of a pulsed jet is significantly different than that of a starting jet because when rings are generated in a repeated fashion, the interaction between rings alters the dynamics of jet shear layer and vortex formation. This is demonstrated in a recent study in which the limiting formation time is reduced significantly when a pulsed jet generates consecutive vortex rings in close proximity. The formation time alone is not sufficient to describe the ring formation process and the pulsing frequency also plays a significant role. To fully exploit the potential of pulsed-jet propulsion, it is imperative to investigate the influence of vortex interaction on ring formation and establish the limiting ring formation process and its optimization for a pulsed jet. In this proposed project, experimental studies will be performed to investigate the formation process of consecutive vortex rings from a pulsed jet and to determine the effects of ring interaction on the shear layer dynamics and ring formation process. The research will emphasize vortex ring growth and its limit, as a dynamical systems analysis will be used to quantify entrainment and identify pinch-off. The dependency of the limiting formation time on the pulsing frequency will be established. Thrust generated from a pulsed jet will be quantified and correlated with ring formation dynamics. A theoretical model will then be developed to predict ring pinch-off and to explain the empirical results. A numerical framework will also be developed to optimize the kinematics of the pulsed jet for vortex ring formation and propulsion. Many features of biological systems that act as constraints in optimal ring formation will also be explored, including stopping vortices formed during recovery strokes, time-dependent jet velocity profile, periodic variation in propulsion velocity, etc.
Intellectual Merit: The proposed project will advance the understanding of vortex ring formation from a pulsed jet, and elucidate the effects of vortex interaction on jet shear layer dynamics and ring formation. It will establish the limiting ring growth process for a pulsed jet, as well as its optimization for propulsion. The knowledge obtained in the project will serve as the guideline for applications of pulsed-jet propulsion, a promising design for future aerial/underwater vehicles. In addition, the understanding on various constraints in optimal ring formation inherent in biological systems, as well as on their adaptations to these constraints, will not only contribute insights to the fields of biological locomotion and integrated biological systems but also complement existing design principles of engineering propulsion systems.
Broader Impacts: The project will explore many fundamental fluid dynamics questions regarding vortex ring formation and interaction. It will have potentially wide applications in the emerging field of pulsed-jet propulsion and will further advance this novel propulsion technique. The proposed project will allow education and training for both undergraduate and graduate students. The PI will develop a new lab component (flow visualization and measurement) for the Fluid Mechanics Lab course at the University of Alaska Fairbanks. The experimental equipment used in the project will be utilized for students practice in this course, and also as demonstration in another course, Propulsion. The proposed research will also be translated into new educational curricula that are accessible to future generations of engineers and biologists alike. The PI will develop a new multi-disciplinary course, Biomechanics and Bio-inspired Design, for the Mechanical Engineering and Biology curriculum at UAF. Most Alaska students, especially Alaska Native students, love nature and this proposed course would appeal to many of them and generate interest in engineering disciplines. The project will also serve K-12 students from the State of Alaska through outreach programs such as Alaska Summer Research Academy and Alaska Native Science & Engineering Program. These opportunities for training and mentorship will be directed toward the underrepresented Alaska Native students.
