An experimental study of the effects of wall conductivity, non-uniform magnetic fields and variable-area ducts on liquid metal flows at high Hartmann number. Part 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 [Lt ] 1. In all but one respect this is the prototype problem analysed by Holroyd & Walker (1978): their analysis required that N [Gt ] 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.