Simulation of magneto-rheological fluids incorporating hydrodynamic effects

The magneto-rheological (MR) response, like the better studied electro-rheological (ER) response, refers to the rapid and reversible viscosity increase seen in certain types of suspensions. The development of a 3D numerical simulation that is able to model the microstructural evolution of MR suspensions including hydrodynamic inter-particle interactions was reported. The current method is essentially a reduced version of the Stokesian Dynamics (SD) method([1]) with modifications to model the MR response. MR particles were modeled as rigid magnetizable spheres suspended in a Newtonian fluid. The Rotne-Prager Yamakawa tensor was used in the construction of the resistance matrix. Wall hydrodynamics were included with a formulation for sphere-wall interactions. MR forces were incorporated using superimposed sphere-pair dipole interaction forces. In simulations, particle cluster formations were observed, and the rheological responses due to these formations were examined. Some basic flow scenarios were studied, including periodic infinite shear flow under a constant magnetic field. MR suspensions are prone to suffer from sedimentation when unused. Their response may therefore be sluggish after an extended period of rest. We apply the simulation to the case of the re-suspension of sedimented suspensions (both normal and MR).