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Hydrodynamic fluctuations and instabilities in ordered suspensions of self-propelled particles

R. Aditi Simha·Sriram Ramaswamy
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Abstract

We construct the hydrodynamic equations for {\em suspensions} of self-propelled particles (SPPs) with spontaneous orientational order, and make a number of striking, testable predictions:(i) SPP suspensions with the symmetry of a true {\em nematic} are {\em always} absolutely unstable at long wavelengths.(ii) SPP suspensions with {\em polar}, i.e., head-tail {\em asymmetric}, order support novel propagating modes at long wavelengths, coupling orientation, flow, and concentration. (iii) In a wavenumber regime accessible only in low Reynolds number systems such as bacteria, polar-ordered suspensions are invariably convectively unstable.(iv) The variance in the number N of particles, divided by the mean , diverges as $ ^{2/3}$ in polar-ordered SPP suspensions.

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R. Aditi Simha, Sriram Ramaswamy. 2002-03-19. Hydrodynamic fluctuations and instabilities in ordered suspensions of self-propelled particles. https://doi.org/10.1103/physrevlett.89.058101

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