Multifluid model simulations of gravitational instabilities in fluidized binary granular materials

Predicting granular flow using continuum approaches is fundamental to advance granular physics and industrial applications. Previous studies have demonstrated that continuum modeling can capture some hydrodynamic instability analogs in monodisperse granular materials. Recently, a family of gravitational instabilities was found between two types of grains, including a Rayleigh-Taylor analog, a granular bubble rising, a granular droplet splitting and particle segregation. The high packing fraction and bi-disperse nature of these flows allow for new challenges to continuum models. Herein, we applied multifluid modeling (MFM) that treats the gas phase and two separate granular phases as fully interpenetrating continua to simulate these instabilities and compared them with newly conducted experiments. Simulation results reproduced all of the four instabilities and demonstrated that frictional particle stress and solids-solids drag are needed to capture critical qualitative flow features. This study can serve as a basis for challenging future particle stress and solids-solids drag models.