Velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating (RMF) and a traveling magnetic field (TMF). In a cylindrical container, a RMF alone, as well as a TMF alone, cause axisymmetric volume forces, which drive corresponding axisymmetric base flows. The combination of both fields gives rise to an inherent three-dimensional constituent of the electromagnetic force distribution. In the case of equal RMF and TMF frequencies, this combination drives a three-dimensional flow consisting of a single large-scale helical motion, which implies an intense mixing of the melt. The necessary admixture of a TMF to a given RMF to cause a qualitative change of the flow structure is shown to be two orders of magnitude smaller in the case of equal field frequencies compared to the case of differing frequencies.
Rayleigh-Bénard convection is not only a classical problem in fluid dynamics but plays also an important role in many metallurgical and crystal growth applications. The measurement of the flow field and of the dynamics of the emerging large-scale circulation in liquid metals is a challenging task due to the opaqueness and the high temperature of the melts. Contactless inductive flow tomography is a technique to visualize the mean three-dimensional flow structure in liquid metals by measuring the flow induced magnetic field perturbations under the influence of one or several applied magnetic fields. In this paper, we present first measurements of the flow induced magnetic field in a Rayleigh-Bénard setup, which are also used to investigate the dynamics of the large-scale circulation. Additionally, we investigate numerically the quality of the reconstruction of the three-dimensional flow field for different sensor configurations.
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