Amazing stuff!
"... "We invented new types of gears that engage by spinning up fluid rather than interlocking teeth—and we discovered new capabilities for controlling the rotation speed and even direction," ...
To explore this, the researchers conducted an intricate series of experiments that included immersing cylinders, or rotors, in liquid—a glycerol-water solution whose properties, such as viscosity and density, the researchers could manipulate.
In these experiments, one cylinder was actively powered to rotate while the other was unpowered or passive. The researchers hypothesized that the active cylinder could generate fluid flows to cause the passive one to rotate. ..."
From the abstract:
"Flow-mediated interactions between objects are important in sedimentation and collective locomotion. New phenomena arise in systems that are dominantly coupled by rotation, as relevant to active matter physics and biological and engineering contexts.
Here we establish an experimental platform for studying fluid mechanical spin-coupling effects and map out how interactions depend on proximity, confinement, and flow state.
The two-body problem of a driven rotor inducing spin of a passive rotor reveals a gearlike counterrotation mode but also surprising corotation modes that occur broadly across the parameter space.
Streamline analysis and a mechanical model indicate distinct transitions between modes that arise geometrically at close range, topologically due to flow reconfiguration, and inertially with increasing Reynolds number.
These findings provide ways to understand, control, and exploit hydrodynamic spin-spin interactions in applications."
Hydrodynamic Spin-Coupling of Rotors (no public access)
Two spinners inside a circular container and surrounded by liquid with bubbles that help to visualize the flows. The left spinner is actively driven to rotate with a motor (not shown) and the right one passively rotates due to the flows.
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