LU14260 - Granular
materials are ubiquitous in nature and industry. Typical examples are
sand on the beach, a drug powder at a pharmaceutical plant, and even the
dust and soil covering the surfaces of planets, satellites and small
bodies of our Solar System. While flows of granular materials are often
studied, a complete set of equations governing these flows is still
undiscovered.
In other words, the power to predict
granular flows is often faced with large uncertainties despite the
existing efforts made to develop sophisticated models.
As
an example, little is known about the role of gravity in these flows, as
gravity is fixed on Earth, while it is much smaller on celestial bodies
such as asteroids, and even on the Moon or Mars.
By using
the unique gravitational environment available onboard the Zero-G
aircraft, we have performed experiments to investigate the role of
gravity in a granular flow. This allows us to explore the behavior of
granular material in conditions that become very close to the ones
encountered on the surface of much smaller bodies than the Earth.
In
normal gravity the flow has two components: the bulk flow that we
induce, and a secondary “convective-like” flow. The characteristics of
convective-like flows are crucial in industrial applications such as
segregation by size, shape, and density, as well as astrophysical
questions, such as understanding the behavior of soil on planetary
surfaces. We find the secondary flow is suppressed in zero gravity, and
enhanced in high gravity. We suggest that gravity tunes the frictional
particle-particle and particle-wall interactions that drive the
convective-like flow, and present measurements to support this. Such an
understanding of the role of gravity is important to interpret the
images of granular surfaces sent by space missions visiting other solid
bodies of our solar system and to prepare future missions – robotic or
manned – which will interact with those surfaces.
