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Journal Article

Defect turbulence in a dense suspension of polar, active swimmers


Rana,  Navdeep
Max Planck Institute for Dynamics and Self-Organization, Max Planck Society;

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Rana, N., Chatterjee, R., Ro, S., Levine, D., Ramaswamy, S., & Perlekar, P. (2024). Defect turbulence in a dense suspension of polar, active swimmers. Physical Review E, 109: 024603. doi:10.1103/PhysRevE.109.024603.

Cite as: https://hdl.handle.net/21.11116/0000-000F-364E-E
We study the effects of inertia in dense suspensions of polar swimmers. The hydrodynamic velocity field and the polar order parameter field describe the dynamics of the suspension. We show that a dimensionless parameter R (ratio of the swimmer self-advection speed to the active stress invasion speed [Phys. Rev. X 11, 031063 (2021)]) controls the stability of an ordered swimmer suspension. For R smaller than a threshold R1, perturbations grow at a rate proportional to their wave number q. Beyond R1 we show that the growth rate is O(q2) until a second threshold R=R2 is reached. The suspension is stable for R>R2. We perform direct numerical simulations to characterize the steady-state properties and observe defect turbulence for R<R2. An investigation of the spatial organization of defects unravels a hidden transition: for small R≈0 defects are uniformly distributed and cluster as R→R1. Beyond R1, clustering saturates and defects are arranged in nearly stringlike structures.