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

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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.