Understanding Pulsatile Helical Flow: Scaling, Turbulence, and Helicity Control

脉动和三维螺旋流动是各种生理流体传输现象的显著特征，尤其普遍存在于心血管循环中，包括心腔、主动脉弓、动脉分叉和大静脉。脉动螺旋流被广泛认为是一种自然优化的机制，可以减少振荡壁面剪应力，减轻颗粒粘连，并增强质量灌流。血流螺旋度的降低与动脉粥样硬化的风险增加有关。尽管脉动螺旋流的研究十分普遍且意义重大，但对脉动螺旋流的时空特性缺乏全面的实验研究和系统的认识。因此，该项目的主要目标是建立一个广泛的脉动螺旋流实验数据库，重点研究其标度规律、稳定性和螺旋度控制。该项目还将促进多年的教育项目，包括高级设计项目、本科研究项目、针对当地K-12学生的外展活动以及北达科他州的培育美国部落本科研究教育项目。该项目的目标是通过一系列实验实现对脉动流的定量了解，主要集中在三个研究目标：(1)建立脉动层流中全局螺旋度的标度规律；(2)研究流动螺旋度对湍流起始阈值的影响；(3)探索螺旋度产生和控制的新的被动机制。该项目将利用台式脉动流动产生系统和具有不同曲率和扭转的标准螺旋容器模型。定量的流动数据将使用时间分辨粒子图像测速仪、层析成像、激光多普勒风速仪以及高频压力和流量传感器来获得。该项目将增进一般流体动力学、生物流动和生理学领域的知识。标度律和湍流起始分析将揭示整体螺旋度和临界雷诺数作为脉动流动频率和振幅的函数。该项目将探索使用螺旋螺旋度诱导剂和血管锥化作为潜在的被动螺旋度产生和控制机制，为药物输送和心血管治疗等不同领域的创新应用铺平道路。此外，主要的更广泛的影响目标包括：(1)实施研究型教育计划，通过高级设计和资助学者计划项目，每年至少有10名本科生参与；(2)开发外联项目，让年轻一代和具有不同背景的学生参与STEM教育。该项目由流体动力学、生物医学系统工程和既定的激励竞争研究计划(EPSCoR)共同资助。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Pulsatile and three-dimensional helical flow is a prominent characteristic in various physiological fluid transport phenomena, notably prevalent in cardiovascular circulations, including heart chambers, the aortic arch, arterial bifurcations, and large veins. Pulsatile helical flow is widely believed to be a naturally optimized mechanism for reducing oscillatory wall shear stress, alleviating particle adhesions, and enhancing mass perfusion. A reduction in the helicity of blood flow has been associated with an elevated risk of atherosclerosis. Despite its prevalence and significance, there is a lack of comprehensive experimental research and a systematic understanding of the spatiotemporal characteristics of pulsatile helical flow. Therefore, the main goal of the project is to establish an extensive experimental database for pulsatile helical flow, focusing on its scaling laws, stability, and helicity control. The project will also facilitate multi-year educational programs, including senior design projects, undergraduate research programs, and outreach activities for local K-12 students and the Nurturing American Tribal Undergraduate Research Education programs in the state of North Dakota.The objective of this project is to achieve a quantitative understanding of pulsatile flow through a series of experiments, focusing on three research aims: (1) Establishing scaling laws for global helicity in pulsatile laminar flow; (2) Investigating the influence of flow helicity on turbulence onset thresholds; (3) Exploring novel passive mechanisms for helicity generation and control. The project will utilize a bench-top pulsatile flow generation system and standard helical vessel models with varying curvatures and torsions. Quantitative flow data will be obtained using time-resolved particle image velocimetry, tomography, laser Doppler anemometry, and high-frequency pressure and flow sensors. The project will advance knowledge in the fields of general fluid dynamics, biological flow, and physiology. Scaling law and turbulence onset analysis will reveal the global helicity and critical Reynolds numbers as a function of pulsatile flow frequency and amplitude. The project will explore the use of spiral helicity inducers and vessel tapering as potential passive helicity generation and control mechanisms, paving the way for innovative applications in diverse fields such as drug delivery and cardiovascular therapeutics. Additionally, the major broader impact objectives include: (1) Implementing research-based educational programs to involve at least ten undergraduate students annually through senior design and grant scholars program projects; (2) Developing outreach projects to engage the younger generation and students with diverse backgrounds in STEM education. This project is jointly funded by the Fluid Dynamics, Engineering of Biomedical Systems, and the Established Program to Stimulate Competitive Research (EPSCoR) programs.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.