Tuning a magnetic field to generate spinning ferrofluid droplets with controllable speed via nonlinear periodic interfacial waves

Two-dimensional free surface flows in Hele-Shaw configurations are a fertile ground for exploring nonlinear physics. Since Saffman and Taylor's work on linear instability of fluid-fluid interfaces, significant effort has been expended to determining the physics forcing that set growth rate. However, stability does not always imply stability. We demonstrate how combination radial an azimuthal external magnetic field can manipulate interfacial shape linearly unstable ferrofluid droplet configuration. show weakly theory be used tune initial growth. Then, nonlinearity arrests leads permanent deformed shape. Specifically, we into motion with predictable rotation speed, demonstrating traveling waves interface. The most wave number combined strength applied fields determine shape, which asymmetric.