2001/05/21 by GERMAN DRAZER, G. Drazer, J. Koplik +5 · 3 citations
Chemistry · Engineering · Materials Science · Physics and Astronomy · #Composite Material Mechanics #Electrostatics and Colloid Interactions #Material Dynamics and Properties #cond-mat.stat-mech #nlin.CD #physics.flu-dyn
paper · pdf · doi:10.1017/s0022112002008261
published as J. Fluid Mech. 460, 307 (2002) · Submitted to J. Fluid Mech
arxiv created 2001/05/21 · openalex publication_date 2002/06/10 · arxiv updated 2009/11/30 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
The dynamics of macroscopically homogeneous sheared suspensions of neutrally buoyant, non-Brownian spheres is investigated in the limit of vanishingly small Reynolds numbers using Stokesian dynamics. We show that the complex dynamics of sheared suspensions can be characterized as a chaotic motion in phase space and determine the dependence of the largest Lyapunov exponent on the volume fraction ϕ. We also offer evidence that the chaotic motion is responsible for the loss of memory in the evolution of the system and demonstrate this loss of correlation in phase space. The loss of memory at the microscopic level of individual particles is also shown in terms of the autocorrelation functions for the two transverse velocity components. Moreover, a negative correlation in the transverse particle velocities is seen to exist at the lower concentrations, an effect which we explain on the basis of the dynamics of two isolated spheres undergoing simple shear. In addition, we calculate the probability distribution function of the transverse velocity fluctuations and observe, with increasing ϕ, a transition from exponential to Gaussian distributions. The simulations include a non-hydrodynamic repulsive interaction between the spheres which qualitatively models the effects of surface roughness and other irreversible effects, such as residual Brownian displacements, that become particularly important whenever pairs of spheres are nearly touching. We investigate, for very dilute suspensions, the effects of such a non-hydrodynamic interparticle force on the scaling of the particle tracer diffusion coefficients D y and D z , respectively, along and normal to the plane of shear, and show that, when this force is very short-ranged, both are proportional to ϕ 2 as ϕ → 0. In contrast, when the range of the non-hydrodynamic interaction is increased, we observe a crossover in the dependence of D y on ϕ, from ϕ 2 to ϕ as ϕ → 0. We also estimate that a similar crossover exists for D z but at a value of ϕ one order of magnitude lower than that which we were able to reach in our simulations.