Instability of concentrated particle suspensions in oscillatory channel flow

GARCIA, A. A.; ROHT, Y. L.; GAUTHIER, G.; SALIN, D.; HULIN, J.P.; DRAZER, G.; IPPOLITO, I.

Virtual

Conferencia; 14th Northeast Complex Fluids and Soft Matter Workshop Friday; 2021

Themotion of individual particles has been tracked experimentally in anon-Brownian suspension of non-buoyant spheres (volume fraction between 0.2 and0.4) subject to a square-wave oscillatory flow in a Hele-Shaw cell at lowReynolds numbers. We investigated the evolution of the suspension structure andvelocity profile, as well as the microscopic reversibility of the particletrajectories, as a function of the amplitude A and period T of the oscillatingflow. At short times, the flow is parallel with a blunted parallel velocity anda corresponding increase of particle concentration at the center of thechannel, consistent with previous results and shear-induced migration models.The reversibility of the motion of the particles from one period to the next isstrong in the center region but much weaker close to the walls. At longertimes, an instability induces an exponential growth in the motion of theparticles transverse to the flow, forming a periodic structure or recirculatingzones along the channel. The wavelength and transverse velocity have beenstudied as a function of A and T. The reversibility of the particle motion isstrongly reduced in this regime. We also discuss the presence of a thresholdvalue in the cumulative strain for the appearance of the instability.