# Berlin 2012 – wissenschaftliches Programm

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# DY: Fachverband Dynamik und Statistische Physik

## DY 16: Fluid dynamics and turbulence II

### DY 16.1: Topical Talk

### Mittwoch, 28. März 2012, 10:00–10:30, MA 144

**Pepsi**^{®}**–or ◯̴ interfacial instabilities between magnetic/non-magnetic liquids** — •Reinhard Richter — Experimentalphysik 5, Universität Bayreuth

Turn a can upside down and lift the pull-tab! The heavier liquid will start to leave the
vessel through the small orifice, whereas air tries to enter it from below.
This unstable condition is known as Rayleigh-Taylor instability. For magnetic beverages it may become *stable* by applying a rotating magnetic field, oriented parallel to the flat interface [1]. We present a first experimental confirmation [2] of this prediction and measure the shape of the interface for different magnetic fields utilizing radioscopy [3].

On the contrary, a magnetic liquid layer will become *unstable* if the field is oriented normally to the interface, and a critical field strength is surpassed. The resulting Rosensweig instability is measured in a highly viscous ferrofluid via a sequence of magnetic pulses. This allows us to catch the phase space dynamics, and to
reconstruct the underlying fully nonlinear equation of motion of the pattern amplitude [4]. When exploring the control parameter-phase space, localized states are uncovered next to the unstable branch of the bifurcation diagram.

[1] D. Rannacher and A. Engel, Phys. Rev. E **75**, 016311 (2007).
[2] A. Poehlmann, Diplomarbeit, Universität Bayreuth (2011).
[3] R. Richter and J. Bläsing, Rev. Sci. Instrum. **72**, 1729 (2001).
[4] C. Gollwitzer, I. Rehberg, and R. Richter, New J. Phys. **12**, 093037 (2010).