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This paper presents an experimental study of the momentum and heat transport in a turbulent magnetohydrodynamic duct flow with strong wall jets at the walls parallel to the magnetic field. Local turbulent flow quantities are measured by a traversable combined temperature-potential-difference probe. The simultaneous measurements of time-dependent velocity and temperature signals facilitates the evaluation of Reynolds stresses and turbulent heat fluxes. Integral quantities such as pressure drop and temperature at the heated wall are evaluated and compared with results from conservative design correlations. At strong enough magnetic fields the destabilizing effect of strong shear generated at the sidewalls wins the competition with the damping effect by Joule's dissipation and turbulent side layers are created. Due to the strong non-isotropic character of the electromagnetic forces, the turbulence structure is characterized by large-scale two-dimensional vortices with their axis aligned in the direction of the magnetic field. As most of the turbulent kinetic energy is concentrated in the near-wall turbulent side layers, the temperatures at the heated wall are governed by the development of the thermal boundary layer in the turbulent flow.

Magnetohydrodynamics (MHD) offers a unique opportunity to study the behavior of two-dimensional turbulent flows. A strong external magnetic field B perpendicular to the flow direction of an electrically conducting fluid will suppress velocity gradients in the direction of B. The resulting approximation is known as quasi-two-dimensional MHD. An experimental configuration is presented which meets this requirement, along with a spatially extended probe used to visualize the two-dimensional flow kinematics inside the opaque liquid metal flow. As a prototypical example, the wake behind a circular cylinder is investigated for Reynolds numbers up to R=10 000. New and unexpected vortex patterns are observed that deviate significantly from usual hydrodynamic flows. Also, stability limits for the transition from stationary to nonstationary flow patterns are experimentally determined for the cylinder wake and another type of shear flow profile. These results confirm existing theoretical predictions and thus validate the quasi-two-dimensional approach.

This paper reports on recent research into magnetohydrodynamic (MHD) phenomena applicable to fusion technology. In Europe, experiments on the relative enhancement of heat transfer in liquid metal (LM) flows in ducts with electrically thin or insulated walls show a factor of two increase due to strong shear flow boundary layers when compared to slug flow solutions. This increase has no associated increase in pressure drop. Stronger enhancement is possible with mechanical promoters, but pressure drop increased concomitantly. Electrical turbulence promoters have been shown in theory to aid in heat transfer as well, although preliminary experiments in Europe show no enhancement and a 20% increase in pressure drop. Experiments in Japan show that the maximum enhancement for liquid Lithium occurs for values of the interaction parameter in the N =10 -20 range. Other recent experimental efforts in Europe, Japan and Russia on natural convection in the presence of magnetic field, formation of insulator coatings and modeling of insulator imperfections are also described. In the USA, design and analysis of liquid systems utilizing all-liquid walls have lead to interest in turbulence simulations for heat transfer at free surfaces of both LMs and Flibe. Free surface flows are particularly sensitive to changes in MHD drag since no applied pressure can be used to drive the free surface flow. For this reason, Flibe is considered a prime candidate for liquid walls and is also considered in Japan as the top candidate for Large Helical Device (LHD) breeder blanket. Experimental work with Flibe simulants is currently underway in Japan, and under development in the USA. Analysis of LM flows under liquid wall conditions is being performed in the USA as well. In Russia some further experiments were made for divertor/first wall LM free surface flow, LM heat pipes and porous structures with Li evaporation.

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