Fields of interest

  • Magnetohydrodynamics: Dynamo Theory and Experiments, Convection, Rotating Fluids
  • Astrophysics: Geodynamo, Planetary and Stellar Dynamos
  • Computational Physics: GPU programming, Direct numerical simulations

The DRESDYN precession dynamo at HZDR

Cosmic magnetic fields are ubiquitous phenomena that are intrinsically coupled to most astrophysical objects like planets, stars or galaxies. The origin of cosmic magnetic fields involves the formation of electrical currents by means of a complex flow of a conducting fluid or plasma. This process, the so called dynamo effect, is necessarily three dimensional and non-linear which makes an analytical or numerical approach difficult. Meanwhile, fluid flow driven generation of magnetic fields has also been obtained in laboratory experiments providing a complementary tool to astronomical observations or direct numerical simulations. However, whereas astrophysical dynamo action is comparably easy because of the large dimensions of the involved flows, its experimental realization requires considerable technical efforts.

The planned liquid sodium facility DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) is a new platform for a variety of liquid sodium experiments devoted to problems of geo- and astrophysical magnetohydrodynamics. Most ambitious experiment will be a large-scale precession driven dynamo experiment. The experiment is motivated by the idea of a precession-driven flow as a complementary energy source for the geodynamo (Malkus, Science 1968, 160, 3825) or the ancient lunar dynamo (Noir et al., ...; Dwyer, Nature 2011, 479, 7372).

Sketch of the precession dynamo experiment

Sketch of the precession dynamo experiment. The cylinder has radius R=1 m and height H=2 m. The tilt between rotation axis and precession axis can be varied from 45º to 90º.

The experiment will consist of a cylinder with radius R = 1 m and height H = 2 m that will rotate around its symmetry axis with a frequency of up to νc = 10 Hz and precess around a second axis with up to νp = 1 Hz (see left panel in figure 1). I am responsible for numerical studies on the behavior of a precession-driven flow in a cylinder in order optimize the design data of the large scale experiment and to provide detailed measurements on the flow behavior in dependence of the rotation rate (parameterized by the Reynolds number Re = 2πνcR2/ν) and the precession ratio Po = νpc. My studies focus on non-linear hydrodynamic simulations with moderate precessional forcing in order to complement flow measurements performed at a small scale water experiment. The hydrodynamic simulations provide flow amplitudes and flow geometry, which serve as input for kinematic dynamo simulations that allow an assessment
in which parameter ranges the occurrence of dynamo action is most likely.

In the strongly non-linear regime the flow essentially consists of the directly forced Kelvin mode superimposed by standing inertial waves that result from non-linear self-interaction of the forced mode. Time-dependent contributions in terms of randomly distributed small-scale noise remain negligible. Most remarkable feature is the occurrence of a resonant-like axisymmetric mode around a precession ratio of Omega_prec/Omega_cyl = 0.1. Kinematic dynamo models show that the combination of this axisymmetric mode and the forced m=1 Kelvin mode is indeed capable of driving a dynamo. Our simulations yield a critical magnetic Reynolds number of Rmc=430 which is well within the regime that will be achieved in the experiment.

Selected Publications

Nonlinear large scale flow in a precessing cylinder and its ability to drive dynamo action

André Giesecke, Tobias Vogt, Thomas Gundrum, and Frank Stefani
Phys. Rev. Lett. – accepted 10 December 2017 

Parametric instability in periodically perturbed dynamos

André Giesecke, Frank Stefani, and Johann Herault
Phys. Rev. Fluids 2, 053701 – Published 19 May 2017

Synchronized Helicity Oscillations: A Link Between Planetary Tides and the Solar Cycle?

Frank Stefani, André Giesecke, Norbert Weber, and Tom Weier

Sol. Phys 291, 8, 2197 - 2212 – Published 1 September 2016

Subcritical transition to turbulence of a precessing flow in a cylindrical vessel

Johann Herault, Thomas Gundrum, André Giesecke, and Frank Stefani

Phys. Fluids 27, 124102 – Published 21 December 2015

Triadic resonances in nonlinear simulations of a fluid flow in a precessing cylinder

André Giesecke, Thomas Albrecht, Thomas Gundrum, Johann Herault, and Frank Stefani

New J. Phys. 17, 113044 – Published 18 November 2015

Magnetic material in mean-field dynamos driven by small scale helical flows

André Giesecke, Frank Stefani, and Gunter Gerbeth

New J. Phys. 16, 073034 – Published 24 July 2014

Forward and inverse problems in fundamental and applied magnetohydrodynamics

André Giesecke, Frank Stefani, Thomas Wondrak, and Mingtian Xu

Europ. Phys. J. ST 220, 1, 9 - 23 – Published 26 March 2013

Spectral properties of oscillatory and non-oscillatory α²-dynamos

André Giesecke, Frank Stefani, and Gunter Gerbeth

Geophys. Astrophys. Fluid Dyn. 107, 1 - 2, 45 - 57 – Published 18 April 2012

Influence of high-permeability discs in an axisymmetric model of the Cadarache dynamo experiment

A Giesecke, C Nore, F Stefani, G Gerbeth, J Léorat, W Herreman, F Luddens and J-L Guermond

New J. Phys. 14, 053005 – Published 4 May 2012

Role of Soft-Iron Impellers on the Mode Selection in the von Kármán-Sodium Dynamo Experiment

André Giesecke, Frank Stefani, and Gunter Gerbeth

Phys. Rev. Lett. 104, 044503 – Published 27 January 2010

Numerical simulations of liquid metal experiments on cosmic magnetic fields

Frank Stefani, André Giesecke, and Gunter Gerbeth

Theo. Comp. Fluid Dyn. 23, 6, 405 - 429 – Published 8 Juyl 2009

Kinematic simulation of dynamo action by a hybrid boundary-element/finite-volume method

André Giesecke, Frank Stefani, and Gunter Gerbeth

Magnetohydrodynamics 44, 3, 237 - 252 – Published 1 September 2008

Anisotropic turbulence in weakly stratified rotating magnetoconvection

André Giesecke

Geophys. J. Int. 171, 1017-1028 – Published 30 July 2007

Oscillating α²-dynamos and the reversal phenomenon of the global geodynamo

André Giesecke, Gunther Rudiger, and Detlev Elstner

Astron. Nachr. 326, 8, 693 - 700 – Published 8 September 2005

Geodynamo α-effect derived from box simulations of rotating magnetoconvection

André Giesecke, Udo Ziegler, and Gunther Rudiger

Phys. Earth Planet. Int. 152, 1-2, 90 - 102 – Published 19 Aug 2005