MODELING OF PARTICLE WALL COLLISIONS IN CONFINED GAS PARTICLE FLOWS

This paper demonstrates that numerical simulations of confined particulate two-phase flows require a detailed modelling of particle-wall collisions which includes the wall surface structure and the particle shape. These effects are taken into account by ''irregular bouncing'' models which are based on the statistical treatment of the collision process. In this study, results obtained using various ''irregular bouncing'' models based on the impulse equations for a particle-wall collision are considered and compared with experimental observations. The wall roughness is simulated by assuming that the particle collides with a virtual wall which has a randomly distributed inclination with respect to the plane, smooth wall. A Gaussian distribution for this random inclination showed the best agreement with experimental results. Numerical predictions of a turbulent two-phase flow in a vertical channel, where the particle phase is treated using a Lagrangian approach, showed that the different models applied for a particle-wall collision have a strong effect on the particle velocity fluctuations and the mass flux profiles in the region of fully developed flow. The numerical simulations using the irregular bouncing models yielded considerably higher values for the particle velocity fluctuations, which also agreed better with the experimental values. This effect was most pronounced for large particles, where the distance they need to respond to the fluid flow is larger than the characteristic dimension of the confinement. On the other hand, the motion of small particles is less affected by the choice of the wall-collision model. These effects of the wall roughness on the velocity fluctuations of the dispersed phase have not been considered in previous studies using irregular bouncing models.