Figure 16.
(a) Mean-square displacements 〈(x(t) − x0)2〉 of passive tracer particles advected by the disturbance velocity fields in suspensions of Pushers (i) and Pullers (ii). (b) Effective passive tracer diffusivities, obtained from the data of (a), as functions of the effective volume fraction ν in suspensions of Pushers and Pullers. Inset: passive tracer diffusivities as functions of ν for Puller suspensions. This growth (slope 3.7 × 10−3) is much smaller than that for subthreshold Pusher suspensions (slope 1.2 × 10−2). (Online version in colour.)