Rheology of dense, bidispersed suspensions: Segregative phenomenon induced by a flow perturbation

We have studied the phenomenon of segregation of a non-Brownian dense suspension (volume fraction φ = 0.5) of rigid, inertialess, neutrally buoyant, bidispersed particles, with a large particle-size-ratio a2/a1 = 3, being a1 and a2 the radii of the smaller and larger particles in the suspension, respectively. The particles have been immersed in a plain shear-flow of a Newtonian-fluid at a low Reynolds number. The shear-rate was varied to analyse the whole rheological behaviour of the suspension. To induce the segregation of the larger particles from the smaller ones, we perturbed the underline shear flow by adding a simple sinusoidal wave to the streamwise velocity, with the wavy-variations in the direction of the shear. We carried out a parametric study varying the amplitude and the wavenumber of the sinusoidal disturbance to analyse their relative importance in the onset of the phenomenon of segregation. The study has been performed by means of numerical simulations that tackle the Newton-Euler equations governing the dynamics of the particles. Preliminary results show that the larger particles tend to migrate towards the regions of minimum shear if the amplitude of the perturbation is above a threshold limit. An increasing wavenumber can help to segregate the particles.