老化屈服应力流体中的球形沉降物引起的流动

We have studied the flow induced by a macroscopic spherical particle sett领 in a Laponite
suspension that exhibits a yield stress, thixotropy, and shear thinning. We show that the fluid
thixotropy or aging induces an increase with time of both the apparent yield stress and
shear-thinning properties but also a breaking of the flow fore-aft symmetry predicted in
Hershel-Bulkley fluids yield-stress, shear-thinning fluids with no thixotropy. We have also varied
the stress exerted by the particles on the fluid by using particles of different densities. Although the
stresses exerted by the particles are of the same order of magnitude, the velocity field presents
utterly different features: whereas the flow around the lighter particle shows a confinement similar
to the one observed in shear-thinning fluids, the wake of the heavier particle is characterized by an
upward motion of the fluid negative wake, whatever the fluids age. We compare the features of
this negative wake to the one observed in viscoelastic shear-thinning fluids polymeric or micelle
solutions. Although the flows around the two particles strongly differ, their sett领 behaviors
display no apparent difference which constitutes an intriguing result and evidences the complexity
of the dependence of the drag factor on flow field. 德国LaVision PIV/PLIF粒子成像测速场仪 Imager pro X PIV相机 用于粒子成像测速(PIV)的荧光示踪粒子