  Detailed studies of the intriguing field-dependent dynamics and transport
properties of confined flowing ferrofluids require efficient mesoscopic
simulation methods that account for fluctuating ferrohydrodynamics. Here, we
propose such a new mesoscopic model for the dynamics and flow of ferrofluids,
where we couple the multi-particle collision dynamics method as a solver for
the fluctuating hydrodynamics equations to the stochastic magnetization
dynamics of suspended magnetic nanoparticles. This hybrid model is validated by
reproducing the magnetoviscous effect in Poiseuille flow, obtaining the
rotational viscosity in quantitative agreement with theoretical predictions. We
also illustrate the new method for the benchmark problem of flow around a
square cylinder. Interestingly, we observe that the length of the recirculation
region is increased whereas the drag coefficient is decreased in ferrofluids
when an external magnetic field is applied, compared with the field-free case
at the same effective Reynolds number. The presence of thermal fluctuations and
the flexibility of this particle-based mesoscopic method provides a promising
tool to investigate a broad range of flow phenomena of magnetic fluids and
could also serve as an efficient way to simulate solvent effects when colloidal
particles are immersed in ferrofluids.
