Synopsis: Fluid-Induced Orbital Motion in Zero Gravity

Shaken or stirred? Suspended beads stir themselves when shaken in a new experiment using magnetic levitation.
Synopsis figure
R. J. A. Hill/University of Nottingham

Particles floating “weightless” in a fluid would appear free to go where they please. However, observations show that suspended particles will self-organize because of fluid-mediated forces. A new experiment described in Physical Review Letters explores the hydrodynamic interactions between two small beads levitating in a gravity-canceling magnetic field. When the system is shaken, the beads come together in a mutual attraction and—as the shaking increases—begin an orbital dance. The authors believe this opens the door to further studies of particle-fluid mixtures in the absence of gravity.

On Earth, particles suspended in a fluid are largely confined to the depth where buoyancy and gravity forces balance out, so studies of their self-organization have often been limited to two dimensions. In real zero gravity, as on the International Space Station, suspended particles can assemble in three dimensions, but very few experiments have explored what influence hydrodynamic forces will have in this environment.

To recreate real zero gravity on Earth, Hector Pacheco-Martinez and colleagues from the University of Nottingham, UK, use a strongly varying magnetic field that can levitate small particles—as shown in previous studies. Inside their 17-tesla magnetic system, the team placed a fluid-filled cell with two identical, millimeter-sized spheres. To induce fluid flow, they shook the cell up and down at a rate of around 20 hertz. In response, the beads moved towards each other until they were side-by-side touching. As the amplitude of the shaking increased, the team observed the beads orbiting around each other in the horizontal plane (perpendicular to the shaking direction). The researchers also performed computer simulations that showed the orbiting arises from flow vortices sprouting out from the contact point between beads. – Michael Schirber


Features

More Features »

Announcements

More Announcements »

Subject Areas

Fluid Dynamics

Previous Synopsis

Next Synopsis

Fluid Dynamics

Stripping Away Confusion

Read More »

Related Articles

Focus: More Energy from Ocean Waves
Energy Research

Focus: More Energy from Ocean Waves

A new structure concentrates water wave motion and could lead to improved techniques for harvesting this renewable energy resource. Read More »

Synopsis: Levitating in a Fluid
Fluid Dynamics

Synopsis: Levitating in a Fluid

Researchers have identified a regime in which a magnetic stir bar can be made to levitate while it spins in a fluid. ­­ Read More »

Focus: Fluid Flow through T-Junction Traps More Particles than Expected
Fluid Dynamics

Focus: Fluid Flow through T-Junction Traps More Particles than Expected

Computer modeling shows that surprisingly large regions can trap particles carried by a fluid that is moving steadily through a pipe junction. Read More »

More Articles