Experimental study of cylinder wakes in electrolytes under axial magnetic field
Final Report Abstract
In the framework of the present project we performed experimental investigations of the flow of an electrolyte around a truncated bar with square cross-section subjected to a uniform axial magnetic field produced by a superconducting magnet. A strong H2SO4 electrolyte was used as a working fluid. The governing parameters of our experiment are the Reynolds number Re and the Hartmann number Ha, the latter being a dimensionless measure of the strength of the magnetic field. Our experiments covered the range 5 < Re < 100 and 0 < Ha < 14 thereby giving us access to a particularly interesting regime where the direct observation of the magnetohydrodynamic analog of the Taylor column, namely the “Ludford column”, would be possible. Since commercial PIV technology would have been damaged under the influence of our 5-Tesla magnet, we used low-cost custom-made PIV and visualisation techniques which gave us direct access to flow patterns both in horizontal and vertical planes. For the creeping flow regime corresponding to the low-Re range of our experiment we have, for the first time, successfully visualised the Ludford column and elucidated its geometrical properties. Our experimental results on the Ludford column are found to be in good agreement with numerical solutions of the steady-state equations of magnetohydrodynamics that have been carried out for the parameters of the experiment. For the relatively fast flow regimes (Re>20) we visualised the behaviour of the vortical structures past the truncated bar referred to as rear and attached vortices, which have different orientation with respect of applied magnetic field. As a result of our analysis for the numerous images, we constructed a “phase-diagram” mapping the positions of the rear and attached vortices as functions of Hartmann and Reynolds numbers. These phase diagrams represent a comprehensive data-base that serves as a basis for future investigations at higher Reynolds numbers. Our project has demonstrated for the first time the feasibility and utility of optical flow measurement in electrolyte flows under high magnetic field and paves the road for velocity measurements and visualisations in magnetohydrodynamics with unprecedented spatial resolution.
Publications
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Optical visualization of the flow around a cylinder in electrolyte under strong axial magnetic field, In: Proceedings of the 12th EUROMECH European Turbulence Conference, September 7–10, 2009, Marburg, Germany, page 833
O. Andreev, A. Kobzev, Yu. Kolesnikov, A. Thess
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Experimental study of flows past a magnetic obstacle, In: Proceedings of the 8th PAMIR International Conference on Fundamental and Applied MHD Borgo – Corsica - France September 5 - 9, 2011
M. Rivero, O. Andreev, A. Thess, S. Cuevas
