The turbulent Rayleigh–Taylor instability with background inclined magnetic field

An imposed background mean magnetic field B0 significantly modifies the dynamics of the Rayleigh–Taylor instability. Depending on the orientation of B0, whether parallel or normal to the interface, the outcomes are very distinct. In the former case, the turbulent mixing layer asymptotic growth rate α is almost doubled compared to hydrodynamics, with a strongly reduced degree of mixing. In the second case, α is decreased by roughly 30% and the turbulent dissipation is enhanced. An analytical prediction for the growth rate is derived for any inclination angle β of the background magnetic field. It is obtained by interpolating previous theoretical results for the parallel and normal B0 limit cases. This prediction is then assessed with the use of well-resolved direct numerical simulations of the Navier–Stokes equations within the Boussinesq and magnetohydrodynamics approximations. Parameters such as buoyancy intensity and magnetic field magnitude are chosen so that an asymptotic state is reached before confinement of the largest structures.