Challenges in contactless inductive flow tomography for Rayleigh--Bénard convection cells

M. Sieger - R. Mitra - F. Schindler - T. Vogt - F. Stefani - S. Eckert - T. Wondrak

Helmholtz-Zentrum Dresden-Rossendorf, Institute of Fluid Dynamics, Department Magnetohydrodynamics, Bautzner Landstraße 400, 01328 Dresden, Germany

Abstract
Contactless inductive flow tomography (CIFT) can reconstruct the complex 3-dimensional flow structure of the large-scale circulation in liquid metal filled Rayleigh-Bénard (RB) convection cells. The method relies on the precise measurement of weak magnetic fields induced by currents in the conducting liquid arising from the fluid motion in combination with primary excitation fields. The velocity distribution is reconstructed from the magnetic field measurements by solving a linear inverse problem using the Tikhonov regularization and L-curve method. A number of technical challenges have to be overcome to reach the desired accuracy of the measurement signals. In this paper we will describe our design of a new CIFT set-up for a large RB vessel with a diameter of 320 mm and a height of 640 mm. We outline the major factors perturbing the measurement signal of several tens of nanoteslas and describe solutions to decrease mechanical drifts by thermal expansion to a sub-critical level to enable CIFT measurements for high-Rayleigh number flows. Figs 5, Refs 16.

Key words: contactless inductive flow tomography, large scale circulation, liquid metal flow, Rayleigh-Bénard convection