title: Fluid velocity fluctuations in a suspension of swimming protists.
abstract: In dilute suspensions of swimming microorganisms the local fluid velocity is a random superposition of the flow fields set up by the individual organisms, which in turn have multipole contributions decaying as inverse powers of distance from the organism. Here we show that the conditions under which the central limit theorem guarantees a Gaussian probability distribution function of velocities are satisfied when the leading force singularity is a Stokeslet, but are not when it is any higher multipole. These results are confirmed by numerical studies and by experiments on suspensions of the alga Volvox carteri, which show that deviations from Gaussianity arise from near-field effects.
authors.affiliation: Department of Applied Mathematics and Theoretical Physics, Centre for Mathematical Sciences, University of Cambridge, Wilberforce Raod, Cambridge CB3 0WA, United Kingdom.
authors.forename: Ilia
authors.initials: I
authors.lastname: Rushkin
authors.forename: Vasily
authors.initials: V
authors.lastname: Kantsler
authors.forename: Raymond E
authors.initials: RE
authors.lastname: Goldstein
mesh_terms: D012212:Rheology; D013535:Suspensions; D013550:Swimming / Q000502:physiology; D044446:Volvox / Q000502:physiology*
chemical_list: D013535:Suspensions