Experimental investigation of liquid-metal flows through a sudden expansion at fusion-relevant Hartmann numbers

The available experimental database for three-dimensional magnetohydrodynamic flows in strong magnetic fields, as required for applications to nuclear fusion blankets, is very limited. In order to broaden the knowledge at relevant parameters, experiments have been performed to investigate such flows through a sudden expansion of rectangular ducts at high Hartmann numbers. In accordance with the design for helium cooled lithium lead blankets the duct walls are electrically conducting. Experimental results for pressure distribution along the duct walls have been recorded and compared with results from asymptotic theory. More than 300 electric potential probes have been used to measure the potential distribution on the surface of the ducts. At the expansion the additional pressure drop due to 3D effects caused by the flow redistribution and by the occurrence of recirculating additional electric currents has been identified. The measurements of surface potential confirm the theoretical predictions that at the expansion a large fraction of the flow bypasses the core by flowing in thin layers along the side walls.