Magnus effect in granular media.

Abstract

A spinning ball moving through air experiences a net lift due to the Magnus effect resulting from the pressure difference across its two sides. In this work, with the help of numerical simulations, we present a similar phenomenon on a circular intruder undergoing both translational and rotational motion in a two-dimensional granular medium. The direction of this Magnus lift in a granular medium, irrespective of its area fraction, is opposite to the general direction in viscous fluids in the range of velocities studied. We relate this effect to the switching in the direction of tangential forces, uneven shearing of the force chains, and uneven distribution in the number of contacts across the rotating intruder. Moreover, this is observed for area fractions Φ as low as 0.35 to as high as 0.82, which lies just below the jamming point. Distribution of the contact force around the intruder surface is also studied with respect to the nondimensionalized rotation speed of the intruder. A saturation in the lift to drag ratio is achieved at very high rotation speed, and the ratio is seen to be weakly dependent on the area fraction of the granular medium. The change in local flow fields of velocity, area fraction, and granular temperature around the intruder for several spin ratios is also discussed. The downstream wake of the intruder also deflects in the opposite direction when compared to the case in viscous fluids.