Deviations from spherical shape decrease the growth velocity in granular aggregate collisions – a granular mechanics study

Abstract

ABSTRACT We used granular mechanics simulations to study collisions between spherical aggregates and axisymmetric ellipsoidal aggregates of equal mass. Non-spherical aggregates may be generated, for example, as the result of previous aggregate collisions, either from the merging of aggregates or from fragmentation processes. Of particular interest is the growth velocity, i.e. the critical collision velocity above which the size of the largest post-collision fragment is smaller than the original aggregate size. We find a systematic decrease of the growth velocity with axis ratio of the ellipsoid. The decrease is caused by the ‘rim peel-off’ effect: grain material close to the rims is more readily ejected from the boundaries of aggregates. When considering collisions with ellipsoids of identical semimajor axis, the growth velocity of oblate ellipsoids surpasses that of prolate ellipsoids. Averaging over the orientation of the ellipsoid and over the impact parameters possible in a collision retains the above-mentioned results. The influence of aggregate shape on collision outcomes is of interest, for instance, for codes describing the evolution of dust clouds under collisions.