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Electromagnetic interaction between a permanent magnet and laminar flow of a moving sphere in a conducting liquid
Z. Lyu^{1}
, T. Boeck^{1}
, C. Karcher^{1}
, A. Thess^{2}
^{1} Institute of Thermodynamics and Fluid Mechanics, Technische Universität Ilmenau, P.O. Box 100565, D98684 Ilmenau, Germany
^{2} Institute of Engineering Thermodynamics, German Aerospace Center (DLR), Pfaffenwaldring 3840, 70569 Stuttgart, Germany eMail: Ze.Lyu@tuilmenau.de
Abstract
Lorentz force velocimetry (LFV) is a noncontact electromagnetic flow measurement technique for electrically conducting liquids. It is based on measuring the flowinduced force acting on an externally arranged permanent magnet. Motivated by extending LFV to liquid metal twophase flow measurement, in a previous test we considered the free rising of nonconductive bubbles/particles in a thin tube of liquid metal (GaInSn) initially at rest. We observed that the Lorentz force signals strongly depend on the size of the bubble/particle and on the position, where it is released. Moreover, the force signals cannot be reproduced in detail, which necessitates a statistical analysis. This is caused by chaotic trajectories due to the rising velocities of about ∼ 200 mm/s. Therefore, in this paper, we use an improved setup for controlled particle motions in liquid metal. In this experiment, the particle is attached to a straight fishing line, which suppresses any lateral motion, and is pulled by a linear driver at a controllable velocity (0200 mm/s). For comparison, we solve the induction problem numerically using Oseen's analytical solution of the flow around a translating sphere that is valid for small but finite Reynolds numbers. This simplification is made since the precise hydrodynamic flow is difficult to measure or to compute. The aim of the present work is to check if our simple numerical model can provide Lorentz forces comparable to the experiments. Although Oseen's solution becomes inaccurate near the sphere for finite Reynolds numbers, it provides a foreaft asymmetry of the flow and is globally wellbehaved. It provides an upper limit to the measurement results. We recover the peakdelay of the Lorentz force signals as well.. Figs 13, Refs 11.
Magnetohydrodynamics 53, No. 4, 653666, 2017 [PDF, 2.29 Mb]
