  The nature and behaviour of the drag coefficient of irregularly shaped grains
within a wide range of Reynolds numbers is discussed. Using computational fluid
dynamics (CFD) tools, the behaviour of the boundary layer at high Re has been
determined by applying the Reynolds Averaged Navier-Stokes turbulence model
(RANS). The dependence of the mesh size and the grid resolution in the
modelling are validated with the previous experimental results applied in flow
around isolated smooth spheres. The drag coefficient for irregularly shaped
grains is shown to be higher than that for spherical shapes, also showing a
strong drop in its value at high Re (drag crisis) but lower than that of the
sphere. The influence of the angle of incidence of the flow with respect to the
particle is analysed, where our findings show an interesting oscillatory
behaviour of the drag coefficient as a function of the angle of incidence,
fitting the results to a sine-squared interpolation, predicted for particles
within the Stokes' laminar regime and for bodies with an ellipsoidal shape
(elongated and flattened spheroids) up to Re=2000. The statistical analysis
shows a Weibullian behaviour of the drag coefficient when random polar and
azimuthal rotation angles are considered.
