Perturbing effects of electric potential probes on MHD duct flows

Data for local velocity in liquid metal duct flows exposed to an external uniform magnetic field may be obtained from measurements of electric potential differences recorded by probes that are moved along the channel width. Experiments show an asymmetry in the distribution of the measured transverse potential gradient and its underestimation compared with the one expected from flow-rate measurements. A numerical analysis of magnetohydrodynamic flows around a probe in a rectangular duct has been performed to support the physical interpretation of potential measurements and to study the influence of the instrument itself on the readings. A calibration procedure is suggested, which allows using measurements of potential differences to get reliable data for velocities in the duct.