Metal Pad Roll Instability at Room Temperature Using Pairs of Liquid Metals

Metal pad roll instability is a well known phenomenon that occurs in aluminium reduction cells [1] Since long, scientists and engineers have been searching for an experimental model that recreates the metal pad roll instability in a well controlled laboratory environment. [2] partly succeeded in this task by using GaInSn eutectic alloy in replacement of aluminium and a steel wire array, in replacement of the badly conducting cryolite layer. A rolling wave motion was observed but comparison to fluid based theoretical models remains difficult.
In this talk, we demonstrate that it is possible to observe metal pad roll instability in a centimeter scale cylindrical set-up at room temperature and using different liquid metal pairs as working fluids: gallium liquid metal over mercury (immiscible case) or gallium over GaInSn eutectic alloy (miscible case). Despite the small difference in electrical conductivity, the stability theory of [3] suggests that metal pad roll instability occurs for reasonable values of the imposed magnetic field and electrical current. We confirm this theoretical prediction with some very challenging direct numerical simulations of the multiphase magnetohydrodynamical flow in this set-up, done with our massively parallel solver SFEMaNS [4].