Dynamo action from a laminar non-linear flow in a precessing cylinder

Dynamo action from a laminar non-linear flow in a precessing cylinder

Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.

Within the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) a dynamo experiment is under development in which a precession driven flow of liquid sodium will be used to excite dynamo action. In my presentation I will address preparative numerical simulations and flow measurements conducted at a small model experiment filled with water. The results provide typical flow pattern and flow amplitudes in dependence of precession ratio and Reynolds number and are used for the setup of kinematic dynamo models in order to estimate whether the particular flow is able to drive a dynamo.

In the strongly non-linear regime the flow essentially consists of the directly forced Kelvin mode superimposed by standing inertial waves caused by non-linear self-interaction of the forced mode whereas 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. Only the combination of this axisymmetric mode and the forced m=1 Kelvin mode is capable of driving a dynamo. Our simulations yield a critical magnetic Reynolds number of Rm_c=430 which is well within the regime that will be achieved in the experiment. However, the occurrence of the axisymmetric mode slightly depends on the absolute rotation rate of the cylinder and future experiments are required to indicate whether this instability will persist at the extremely large Re that will be obtained in the large scale experiment.

Keywords: Dynamo; Dresdyn

  • Poster
    MREP 2017, 11.-12.09.2017, Cambridge, Great Britain

Permalink: https://www.hzdr.de/publications/Publ-25966
Publ.-Id: 25966