The Dynamic Coefficient for Collisional Granular Flows at Flat Frictional Walls

This paper derives the expression of dynamic friction coefficient for collisional granular flows at flat walls. An important character of the new expression is that the effect of inhomogeneous of flows on the friction is under the consideration by using the velocity distribution function of particles described by the second-order solution of the Boltzmann equation rather than the Maxwellian velocity distribution. It shows that the inhomogeneous of flows, represented by the velocity gradient of the flows, plays an important role in the friction. Comparisons of the present study with the computer simulation results are presented, which shows that the analytical equation for dynamic friction coefficient agrees well. Furthermore, the influences of different parameters on the dynamic friction coefficient are also investigated, including coefficient of restitution, velocity gradient and solids fraction.