EXPERIMENTAL-STUDY OF THE EFFECTS OF WALL CONDUCTIVITY, NONUNIFORM MAGNETIC-FIELDS AND VARIABLE-AREA DUCTS ON LIQUID-METAL FLOWS AT HIGH HARTMANN NUMBER .1. DUCTS WITH NON-CONDUCTING WALLS

The results are presented of an experimental investigation of the flow of mercury along straight, circular and rectangular non-conducting ducts situated in a magnetic field that is uniform except over a short length of the duct where its value decreases by 50%. Magnitudes of the field strength and mean velocity are such that the Hartmann number M is large, the interaction parameter N ≈ M½ and the magnetic Reynolds number Rm ≪ 1. In all but one respect this is the prototype problem analysed by Holroyd & Walker (1978): their analysis required that N ≫ M½. Distributions of pressure, electric potential and velocity are measured, the latter by hot-film probes. Qualitative agreement with the theoretical predictions is obtained in so far as a pressure drop of O(duct radius × fully-developed flow pressure gradient × M½) occurs over the non-uniform field region and, in the circular duct, the fluid can be seen to migrate towards the centre of the duct upstream and downstream of the non-uniform field region but in that region this tendency is reversed. Similar effects appear to occur in the rectangular duct. © 1979, Cambridge University Press