BRIGE: Optimal formation of consecutive vortex rings for propulsion systems

[1228121]对推进有影响的涡环形成的一个关键水动力特征是涡环的增长是有限制的。研究建立了由启动射流形成孤立涡环的极限过程，并将最优环形成与极限形成时间联系起来。受乌贼和水母等动物的启发，一种利用脉冲射流产生连续漩涡环的新型推进技术已经开发出来。脉冲射流的环的形成过程与启动射流的环的形成过程有显著的不同，因为当环以重复的方式产生时，环之间的相互作用改变了射流剪切层的动力学和涡的形成。最近的一项研究证明了这一点，当脉冲射流在近距离产生连续涡环时，极限形成时间显著缩短。单独的形成时间不足以描述环的形成过程，脉冲频率也起着重要的作用。为了充分发挥脉冲射流推进的潜力，有必要研究涡旋相互作用对环形形成的影响，建立脉冲射流的极限环形形成过程及其优化。本项目将通过实验研究脉冲射流中连续涡环的形成过程，并确定环相互作用对剪切层动力学和环形成过程的影响。这项研究将着重于涡旋环的增长及其极限，因为动力系统分析将用于量化夹带和识别夹断。建立了极限形成时间与脉冲频率的关系。脉冲射流产生的推力将被量化，并与环形形成动力学相关联。然后将开发一个理论模型来预测环掐断并解释经验结果。还将开发一个数值框架来优化脉冲射流的运动学，以形成涡环和推进。生物系统的许多特征也将作为最佳环形成的约束条件进行探索，包括在恢复冲程中形成的停止漩涡，随时间变化的射流速度分布，推进速度的周期性变化等。智力优势：提出的项目将促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，以及它的推进优化。在该项目中获得的知识将为脉冲喷气推进的应用提供指导，这是未来空中/水下航行器的一种有前途的设计。此外，了解生物系统固有的最佳环形成的各种约束，以及它们对这些约束的适应，不仅有助于对生物运动和综合生物系统领域的见解，而且还可以补充现有的工程推进系统设计原则。更广泛的影响：该项目将探索许多关于涡旋环形成和相互作用的基本流体动力学问题。它在脉冲喷射推进这一新兴领域具有广阔的应用前景，将进一步推动这一新型推进技术的发展。拟议的项目将允许对本科生和研究生进行教育和培训。PI将为阿拉斯加费尔班克斯大学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）。项目中使用的实验设备将用于学生在本课程的实践，也将作为另一门课程《推进》的演示。拟议的研究也将被翻译成新的教育课程，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，尤其是阿拉斯加土著学生，热爱大自然，这门课程将吸引他们中的许多人，并激发他们对工程学科的兴趣。该项目还将通过阿拉斯加夏季研究学院和阿拉斯加本土科学与工程项目等外展项目为阿拉斯加州的K-12学生提供服务。这些培训和指导的机会将直接针对代表性不足的阿拉斯加原住民学生。

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.