Fluid dynamic forces acting on irregular shaped particles: Simulations by the Lattice–Boltzmann method

Abstract

Commonly numerical calculations of particle-laden flows are based on the assumption of spherical particles. In practice however, particles are mostly irregular in shape and therefore the spherical particle approximation has to be mistrusted in such cases. Information on the fluid dynamic forces acting on irregular shaped particles is though quite rare. Consequently, the Lattice-Boltzmann method with local grid refinement and curved wall boundary condition was applied to simulate laminar plug flow about fixed irregular shaped particles. For a large number of particle orientations and two sets of four irregular particle types, each with about the same sphericity (i.e. 0.71 and 0.87), the drag, lift and torque coefficients were calculated. From these results distributions of the resistance coefficients were derived for particle Reynolds numbers between 1 and 200. These distributions could be reasonably well approximated by normal distribution functions which are defined by a mean value and a standard deviation. The mean values and the standard deviations of the simulated coefficients for drag, profile lift and torque very well correlate with the particle Reynolds number and are of course depending also on sphericity. Expectedly, the drag coefficient increases with decreasing sphericity. This information may be now used for developing a statistical model for the fluid forces acting on irregular particles in the frame of a Lagrangian approach. Hence, in each tracking time step instantaneous values of the drag, lift and torque coefficients may be drawn from the distributions with given mean value and standard deviation. This approach should mimic the random behaviour of irregular shaped particles.