Multifluid model simulations of gravitational instabilities in fluidized binary granular materials

Abstract

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.

Heat transfer within dynamically structured bubbling fluidized beds subject to vibration: A two‐fluid modeling study

“…The similar bubbling patterns between the freely bubbling fluidized bed and unstructured bubbling fluidized bed vibrated at 2 Hz are due to the fact that the vibration at 2 Hz is too low to induce large effects on the bubbling pattern, as the vibration strength is proportional to the squared vibration frequency according to , where is a constant of 9.81 m/s 2 . In contrast, using a vibration frequency of 8 Hz, the vibration strength is too strong, which has an effect to suppress bubbling 46 . Accompanied by the transition between the solid‐like and fluid‐like states in the bed, the horizontal bands are formed and rising in this bed configuration.…”

“…In contrast, using a vibration frequency of 8 Hz, the vibration strength is too strong, which has an effect to suppress bubbling. 46 Accompanied by the transition between the solid-like and fluid-like states in the bed, the horizontal bands are formed and rising in this bed configuration. Overall, the key features of the simulated solids volume fraction distribution patterns and the dynamic bubbling behaviors in different bed configurations show good agreement with experiments as shown in Figure 2F and Video S2.…”

“…The choice of such modeling approach is to avoid using moving mesh that is computationally expensive and not available in MFiX. As discussed in our previous work, 46 such modeling approach has some differences from the real setup. In the real setup, particles on bottom are impacted by collisions with the moving bottom boundary and particles near the side walls are impacted by frictional contacts with the moving side walls, while particles in the center of the bed are less impacted by the vibration.…”