Propulsive thrust of a driven filament at low Reynolds number with non-uniform flexibility

Abstract eng:
In the low Reynolds number regime, actuating a rigid filament periodically at one end leads to a reciprocal motion and hence produces no propulsive force. Instead if the filament is flexible viscous forces lead to a deformation of the filament and the generation of a net propulsive force (thrust). For a given actuation frequency and filament length, an optimal bending modulus of the filament can be determined to produce the largest propulsive force. Here we explore the possibility of further improving the propulsive performance by allowing variable flexibility along the filament. We demonstrate that by simply dividing a filament into two segments with different bending rigidity a higher propulsive force can be obtained compared with the case of uniform stiffness. The results suggest the possibility of exploiting this new degree of freedom for enhancing propulsion at low Reynolds numbers.

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