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arXiv · 2507.06239

Instabilities and turbulence in extensile swimmer suspensions

Purnima Jain·Navdeep Rana·Roberto Benzi·Prasad Perlekar
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Abstract

We study low Reynolds number turbulence in a suspension of polar, extensile, self-propelled inertial swimmers. We review the bend and splay mechanisms that destabilize an ordered flock. The suspension is always unstable to bend perturbations. Using a minimal 1D model, we show that the splay-stable to splay-unstable transition occurs via a supercritical Hopf bifurcation. We perform high-resolution numerical simulations in 2D to study the varieties of turbulence present in this system transitioning from defect turbulence to concentration-wave turbulence depending on a single non-dimensional number, denoting the ratio of the splay-concentration wavespeed to the swimmer motility.

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Purnima Jain, Navdeep Rana, Roberto Benzi, Prasad Perlekar. 2025-06-20. Instabilities and turbulence in extensile swimmer suspensions. https://doi.org/10.1103/32td-zfcn

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