Hydrodynamic vortex flow in magnetic fluid: Under continuous rotation of a rare earth magnet.

This article focuses on the experimental generation of magnetically driven hydrodynamic vortex flow in magnetizable systems to advance analogue black hole models incorporating magnetic field effects. Two systems were studied under a rotating rare-earth magnet: (i) a pure magnetic fluid composed of surfactant-coated superparamagnetic magnetite nanoparticles suspended in kerosene, and (ii) an immiscible liquid system combining magnetic fluid with a non-magnetic water–n-propanol mixture. While the pure magnetic fluid experienced a continuous magnetic field preventing vortex formation, the immiscible system exhibited three flow regimes—sloshing, vortex, and steady state—depending on the magnetic volume fraction and magnet rotation speed, with stable vortex formation achieved through a balance of magnetic and centrifugal forces. The study employed particle image velocimetry using a smartphone camera to analyze tangential velocity profiles, demonstrating conditions for stable hydrodynamic vortices that may serve as laboratory analogues for magnetic field effects around astrophysical objects such as black holes.