Dancing fibers in a Microscale Burgers-like Vortex

An important category of microscale fluid-structure interactions concerns how flexible fibers deform and interact with fluid flows. Many experimental and numerical studies have focused on shape dynamics of fibers in shear flows, assuming that at such small spatial scales, the local background flow experienced by passive plankton and microswimmers is well-approximated by flows with constant vorticity. Here we move away from this assumption, and study the shape evolution of flexible fibers in a zero Reynolds number analog of a Burgers vortex. This flow is created by the superposition of several regularized singularities of the Stokes equations and has local properties similar to the Burgers vortex, while decaying to zero at infinity. Coupling a Kirchhoff rod-based filament model with the Stokeslet segment framework, we reveal novel shapes exhibiting three-dimensional symmetric deformations, which are absent in typical shear flow experiments. The shape dynamics depend on an appropriately defined nondimensional elastoviscous number and the length of the fiber relative to vortex core diameter. Our model results demonstrate that a fiber’s flexibility influences the time required for it to complete an excursion cycle.