Low Reynolds number swimming of helical structures and rigid spheres
Demir, Ebru (2018) Low Reynolds number swimming of helical structures and rigid spheres. [Thesis]
Micro swimmers have a great potential to realize minimally invasive medical procedures to detect and treat diseases. They are promising candidates for achieving targeted drug delivery, which can reduce the side effects of potent drugs and minimize the secondary complications of dangerous treatments. However, swimming at low Reynolds number environments such as bodily fluids requires breaking the time reversal symmetry to achieve propulsion, therefore swimming of micro structures in viscous environments presents a challenge. In this thesis, swimming characteristics and performance of both chiral and magnetically actuated axisymmetric structures swimming inside cylindrical v conduits at low Reynolds numbers are investigated using computational and numerical models, as well as experimental studies. Computational tools that predict the swimming performance of both chiral and axisymmetric swimmers are presented to provide a comprehensive analysis that considers both types of swimmers used in this research field. Effects of geometric parameters on the swimming performance of chiral structures are analyzed and guidelines for designing helical tails for optimized velocity or efficiency are established using a computational fluid dynamics model. Symmetry breaking with axisymmetric particles is achieved by exploiting their hydrodynamic interactions with confining boundaries. A numerical model based on the resistive force theory that can predict their trajectories with high accuracy is reported. Non-inertial focusing and controlled motion of rigid spheres inside cylindrical channels are experimentally demonstrated. The findings presented contribute to our understanding of the swimming characteristics of both symmetric and asymmetric micro swimmers and pave the way for new applications.
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