Turbulence measurements in a rotating magnetic field driven flow

Abstract

Four-wire electric potential difference probes are used to record time series of two local velocity components in a flow driven by a rotating magnetic field. It is demonstrated that statistical properties of turbulence in an electromagnetically driven flow can be extracted from the signals, although they are predominated by noise, disturbances mainly owing to the operation of switching power supplies in modern installations, and filter characteristics of the data acquisition system. For three physical systems, which are two experimental cells with significantly different sizes filled with different melts and two magnetic systems, it is shown that the micro-Eulerian scale exhibits a power law dependence on the mean flow velocity over a range of the dimensionless driving force, the Taylor number, of more than three orders of magnitude. In terms of Reynolds numbers, this range starts in the transitional regime slightly above the threshold of instability and spreads two orders of magnitude. It is examined whether the flow with the highest velocities might be called a developed turbulent regime. Energy spectra are calculated from the time series and are discussed in the framework of existing theory.