Helicity oscillations in Rayleigh–Bénard convection of liquid metal in a cell with aspect ratio of 0.5

Abstract

In this paper, we present numerical and experimental results on helicity oscillations in a liquid-metal Rayleigh–Bénard convection cell with an aspect ratio of 0.5. While the numerical simulations use the finite volume library OpenFOAM, the experimental results are obtained by means of contactless inductive flow tomography. We find that helicity oscillations occur during transitions of flow states with different roll numbers that are characterized by significant changes in the Reynolds number. However, helicity oscillations are also observed when the number of rolls is constant and the Reynolds number is changing only very slowly. Notably, the helicity oscillations observed during the transient double-roll state exhibit characteristics remarkably similar to those associated with the Tayler instability, which points to a rather generic and universal character of this phenomenon. Helicity oscillations are also discussed as a possible mechanism for synchronizing the solar dynamo by tidal forces of the orbiting planets.