Effect of a magnetic field on stability and transitions in liquid breeder flows in a blanket

• In LM blankets, coolant/breeder flows are expected to be hydrodynamically unstable.
• Possible instabilities are related to either MHD boundary layers or bulk shear layers, typically associated with high-velocity near-wall jets.
• In the mixed-convection flows, two types of turbulence, either weak or strong, have been observed.

We review previous studies on instabilities and transitions in magnetohydrodynamic flows in a special context of liquid-metal blanket applications. In the past, possible transitions in blanket flows were mostly attributed to instabilities in the Hartmann layers. More recent studies show, however, that the side layers can experience instabilities at sufficiently lower Reynolds numbers. This suggests that in the blanket flows, the appearance of turbulence can most likely be related to the side rather than Hartmann layers. Various factors that may affect stability in blanket flows have been discussed. In particular, buoyancy forces can result in potentially unstable inflectional velocity profiles. First computational results, illustrating possibility of instabilities and quasi-two-dimensional turbulence in vertical mixed-convection flows heated volumetrically are presented.