BRIGE: Optimal formation of consecutive vortex rings for propulsion systems

涡环形成的一个关键的水动力学特征是涡环的生长有一个极限。研究建立了起始射流孤立涡环形成的极限过程，并将最佳涡环形成与极限形成时间联系起来。受鱿鱼和水母等动物的启发，利用脉冲射流产生的连续涡环开发了一种新的推进技术。脉冲射流的环形成过程与起始射流的环形成过程显著不同，因为当以重复的方式产生环时，环之间的相互作用改变射流剪切层和涡流形成的动力学。这是证明在最近的一项研究中，其中的限制形成时间显着减少时，脉冲射流产生连续的涡环在附近。单独的形成时间不足以描述环形成过程，脉冲频率也起着重要作用。为了充分发挥脉冲射流推进的潜力，研究涡流相互作用对环形成的影响，建立脉冲射流的极限环形成过程及其优化是十分必要的。 在这个拟议的项目中，将进行实验研究，以调查从脉冲射流连续涡环的形成过程，并确定环的相互作用对剪切层动力学和环的形成过程的影响。研究将强调涡环的增长及其极限，因为动力系统分析将用于量化卷吸和识别夹断。将建立限制形成时间对脉冲频率的依赖性。脉冲射流产生的推力将被量化并与环形成动力学相关。一个理论模型，然后将开发预测环夹断和解释的经验结果。还将开发一个数值框架，以优化涡环形成和推进的脉冲射流的运动学。生物系统的许多特性在最佳环形成中起着约束作用，也将被探索，包括在回收冲程期间形成的停止涡流，随时间变化的射流速度分布，推进速度的周期性变化等。智力优点：该项目将推进对脉冲射流涡环形成的理解，并阐明涡相互作用对射流剪切层动力学和环形成的影响。它将建立脉冲射流的极限环生长过程，以及其对推进的优化。在该项目中获得的知识将作为脉冲喷气推进应用的指导方针，这是未来航空/水下航行器的一种有前途的设计。此外，对生物系统中固有的最佳环形成的各种限制以及它们对这些限制的适应性的理解，不仅将有助于对生物运动和集成生物系统领域的深入了解，而且还将补充现有的工程推进系统的设计原则。该项目将探讨有关涡环形成和相互作用的许多基本流体动力学问题。它将在新兴的脉冲喷气推进领域有潜在的广泛应用，并将进一步推动这一新的推进技术。拟议的项目将为本科生和研究生提供教育和培训。PI将为阿拉斯加大学费尔班克斯的流体力学实验室课程开发一个新的实验室组件（流动可视化和测量）。本计画中所使用的实验设备将用于学生在本课程中的练习，并在另一门课程“推进”中作为示范。拟议的研究还将转化为新的教育课程，供未来几代工程师和生物学家使用。PI将为UAF的机械工程和生物学课程开发一门新的多学科课程，生物力学和生物启发设计。 大多数阿拉斯加学生，特别是阿拉斯加原住民学生，热爱大自然，这门课程将吸引他们中的许多人，并产生对工程学科的兴趣。该项目还将通过阿拉斯加夏季研究学院和阿拉斯加土著科学工程计划等外展计划为阿拉斯加州的K-12学生提供服务。这些培训和指导的机会将针对代表性不足的阿拉斯加土著学生。

Abstract1228121Peng, JifengA 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.