title: Magnetic field induced flow pattern reversal in a ferrofluidic Taylor-Couette system.
abstract: We investigate the dynamics of ferrofluidic wavy vortex flows in the counter-rotating Taylor-Couette system, with a focus on wavy flows with a mixture of the dominant azimuthal modes. Without external magnetic field flows are stable and pro-grade with respect to the rotation of the inner cylinder. More complex behaviors can arise when an axial or a transverse magnetic field is applied. Depending on the direction and strength of the field, multi-stable wavy states and bifurcations can occur. We uncover the phenomenon of flow pattern reversal as the strength of the magnetic field is increased through a critical value. In between the regimes of pro-grade and retrograde flow rotations, standing waves with zero angular velocities can emerge. A striking finding is that, under a transverse magnetic field, a second reversal in the flow pattern direction can occur, where the flow pattern evolves into pro-grade rotation again from a retrograde state. Flow reversal is relevant to intriguing phenomena in nature such as geomagnetic reversal. Our results suggest that, in ferrofluids, flow pattern reversal can be induced by varying a magnetic field in a controlled manner, which can be realized in laboratory experiments with potential applications in the development of modern fluid devices.
authors.affiliation: Institute of Science and Technology Austria (IST Austria), 3400 Klosterneuburg, Austria.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Altmeyer
authors.affiliation: Department of Mathematics, KNU-Center for Nonlinear Dynamics, Kyungpook National University, Daegu, 702-701, South Korea.
authors.forename: Younghae
authors.initials: Y
authors.lastname: Do
authors.affiliation: School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona, 85287, USA.
authors.forename: Ying-Cheng
authors.initials: YC
authors.lastname: Lai