Statistics of a 2D immersed granular gas magnetically forced in volume

TL;DR

This experimental study investigates a 2D magnetically forced granular gas in a fluid, revealing unique velocity distributions and dynamics that differ from boundary-forced granular systems, with implications for understanding energy transfer in such systems.

Contribution

It provides the first detailed experimental analysis of a homogeneously-forced 2D granular gas driven by magnetic torque, highlighting differences from boundary-driven systems.

Findings

Velocity distributions are stretched exponentials with a 3/2 exponent.

No cluster formation or energy equipartition observed.

Conversion rate of angular to linear momentum influences system dynamics.

Abstract

We present an experimental study of the dynamics of a set of magnets within a fluid in which a remote torque applied by a vertical oscillating magnetic field transfers angular momentum to individual magnets. This system differs from previous experimental studies of granular gas where the energy is injected by vibrating the boundaries. Here, we do not observe any cluster formation, orientational correlation and equipartition of the energy. The magnets' linear velocity distributions are stretched exponentials, similar to 3D boundary-forced dry granular gas systems, but the exponent does not depend on the number of magnets. The value of the exponent of the stretched exponential distributions is close to the value of 3/2 previously derived theoretically. Our results also show that the conversion rate of angular momentum into linear momentum during the collisions controls the dynamics of this homogenously-forced granular gas. We report the differences between this homogeneously-forced granular gas, ideal gas, and nonequilibrium boundary-forced dissipative granular gas.