We conduct experiments with force-free magnetically driven rigid helical swimmers in Newtonian and viscoelastic (Boger) fluids. By varying the sizes of the swimmer body and its helical tail, we show that the impact of viscoelasticity strongly depends on the swimmer geometry: it can lead to a significant increase of the swimming speed (up to a factor of 5), a similar decrease (also up to a factor of 5), or it can have approximately no impact. Using an analysis of our data along with theoretical modeling we suggest that the influence of viscoelasticity on helical propulsion is controlled by an asymmetry effect, previously reported for dumbbell swimmers, wherein the front-back size mismatch leads to a non-Newtonian elastic force that can either enhance or hinder locomotion.

• Received 2 December 2020
• Accepted 1 April 2021

DOI:https://doi.org/10.1103/PhysRevFluids.6.043102