Self-diffusion in unbounded rapid granular flows: a nonequilibrium approach

Using a nonequilibrium simulation scheme, the transverse diffusive motion has been investigated in unbounded shear flows of smooth, monodisperse, inelastic spherical particles. This scheme is used to obtain the concentration gradient due to the particle mass flux, which is extracted from the bulk flow using a certain labeling algorithm. The self-diffusion coefficient can then be obtained from Fick's law. Under steady conditions, the simulation results show that the particle diffusivity can be described by a linear law. This finding provides a justification for assuming a linear law relationship in the kinetic theory type derivation of an expression for self-diffusivity. Moreover, the values of self-diffusion coefficient from the computer simulations agree with those obtained using kinetic theory formulations for solid volume fractions less than 0.5.