RESUMO
The aim of this work is to present a lattice Boltzmann (LB) model devoted to dealing with non-Newtonian free surface flow. The combination of LB solver with a free-surface model allows dealing with multiphase flows where the density ratio in between the two considered phases is so high that the lighter phase can be neglected. For this particular set of multiphase models, the interface between the two phases is numerically reconstructed and transported via a diffusion equation. Moreover, the application of a Carreau approach for viscosity modelling allows the introduction of effects related to shear stress on fluid flow evolution. Two different non-Newtonian silicon-like materials have been considered here, namely the polystyrene and acrylonitrile butadiene styrene. Here, the author, after the mandatory model validation with a reference configuration, presents some applications of injection moulding for two different test-cases: the former is the injection in a labyrinth-like gasket, whereas the latter is the injection in a porous media. This article is part of the theme issue 'Fluid dynamics, soft matter and complex systems: recent results and new methods'.
RESUMO
The lattice Boltzmann method (LBM) is routinely employed in the simulation of complex multiphase flows comprising bulk phases separated by nonideal interfaces. The LBM is intrinsically mesoscale with a hydrodynamic equivalence popularly set by the Chapman-Enskog analysis, requiring that fields slowly vary in space and time. The latter assumptions become questionable close to interfaces where the method is also known to be affected by spurious nonhydrodynamical contributions. This calls for quantitative hydrodynamical checks. In this paper, we analyze the hydrodynamic behavior of the LBM pseudopotential models for the problem of the breakup of a liquid ligament triggered by the Plateau-Rayleigh instability. Simulations are performed at fixed interface thickness, while increasing the ligament radius, i.e., in the "sharp interface" limit. The influence of different LBM collision operators is also assessed. We find that different distributions of spurious currents along the interface may change the outcome of the pseudopotential model simulations quite sensibly, which suggests that a proper fine-tuning of pseudopotential models in time-dependent problems is needed before the utilization in concrete applications. Taken all together, we argue that the results of the proposed paper provide a valuable insight for engineering pseudopotential model applications involving the hydrodynamics of liquid jets.
