A 2-D suspension of active agents: the role of fluid mediated   interactions
  Taking into account simultaneously the Vicsek short range ordering and also the far-field hydrodynamic interactions mediated by the ambient fluid, we investigate the role of long range interactions in the ordering phenomena in a quasi 2-dimensional active suspension. By studying the number fluctuations, the velocity correlation functions and cluster size distribution function, we observe that depending on the number density of swimmers and the strength of noise, the hydrodynamic interactions affect the ordering in a suspension. For a fixed value of noise, at large density of particles, long range interactions enhance the clustering in the system. 
Hojjat Behmadi, Zahra Fazli, Ali Najafi
physics.bio-ph cond-mat.soft