Numerical investigation on yielding phenomena of magnetorheological fluid flowing through microchannel governed by transverse magnetic field

Abstract

To investigate the yielding phenomena during the start-up process of a magnetorheological fluid (MRF) flowing through a microchannel under a transverse uniform magnetic field, a three-dimensional and two-phase numerical simulation method is established based on the lattice Boltzmann method, united with the immersed boundary method and the discrete element method. Affected by the transverse uniform magnetic field, the randomly distributed magnetic nanoparticles (MPs) in MRF form some chains parallel to the direction of the magnetic field, and driven by the carrier fluid, the straight chains become curved due to the velocity gradient of the carrier fluid. It is revealed that the yielding process of MRF with water being the carrier fluid is essentially the deformation of the chains composed of MPs. The averaged shear force on the MPs at the ends of chains is taken to characterize the yielding status of an MP cluster, and there exists the maximum shear force during the deformation of chains. The Reynolds number has obvious influence on the characteristic shear force in the single chain, while for a multi-chain system, the chains are entangled with each other during the course of yielding and the characteristic shear force presents a complicated regularity. When the intensity of the magnetic field is relatively small, it has influence on the yielding force; once it is larger than a critical value, the yielding force remains constant. The yielding of MRF flow in a microchannel is a transient experience, and after yielding, the chain-like structure can maintain its integrity along with the channel flow.

Experiments and Simulations on the Magnetorheology of Magnetic Fluid Based on Fe3O4 Hollow Chains

“…In recent years, simulation has become a useful tool in mechanism research of magnetic fluid due to the improvement of computer performance. Several powerful simulation methods have been developed such as molecular dynamics, particle level dynamic simulation, finite element method, computational fluid dynamics, and machine learning method. − Particle level dynamic simulation is a mesoscopic simulation method based on the point-dipole model . This numerical method has been employed to investigate conventional magnetic fluid under different loadings.…”

Immersed boundary conditions for moving objects in turbulent flows with the lattice-Boltzmann method

“…:e n dx: (15) The integration is done between points S and Ref, more precisely between 0 and Dx 2 , following the findings of Shi et al 20 showing that the location of point Q at a distance of Dx=4:0 from the wall yields good results for all the simulations in their work. Then, the previous equation can be expressed in terms of the variables at the Lagrangian points by integrating the viscous terms between the wall and Ref point, and using the mean value theorem for integrals to calculate the other terms…”

“…These operators rely on delta functions defined on a narrow band across the boundary, typically three or four nodes. Despite a large usage of the immersed boundary method for laminar flows in contexts involving flexible, multiphase, magnetic, or porous boundary conditions, [10][11][12][13][14][15][16][17] it is less frequent to encounter studies at high Reynolds number flows, which can be done using Navier-Stokes solvers, 18 and more rarely using the lattice-Boltzmann framework, which is the framework here.…”

Simulations on the rheology of dry magneto-rheological fluid under various working modes

“…Thus, the particles' motion and airflow field must be calculated at each time step. Zhang et al and Fu et al simulated both the microstructures and the flow field in MRF by using the immersed boundary method [24,25]. But the sophisticated model increased the computing complexity and limited the number of particles in one simulation case.…”