Mixing by the Rayleigh-Taylor (R-T) instability in incompressible magnetic fluids is studied with two- and three-dimensional ideal MHD simulations. Evolution and amplification of magnetic fields in the Rayleigh-Taylor instability are explored in the linear and nonlinear regime for various perturbations. In a single-mode perturbation, both tangential and normal magnetic fields to the density interface decrease the growth of instabilities, while a tangential field is more efficient in stabilizing the flow, as predicted by linear theory. However, the growth of a multiple-mode perturbation in the nonlinear regime tends to be enhanced by a normal magnetic field because the flow is collimated along the field lines. A strong tangential field suppresses the growth of short-wavelength modes, as expected from linear theory. Three-dimensional numerical simulations are carried out to study the amplification of magnetic fields in the turbulent mixing layer developed by the instability in the nonlinear regime. We find the following results. (1) The turbulent flow amplifies the magnetic field more efficiently in three-dimensions than in two-dimensions. (2) The peak of the magnetic energy spectrum occurs at high wavenumbers, which means that the field is amplified preferentially on small scales. (3) The peak of the kinetic energy spectrum is at scales significantly longer than the grid scale, is independent of grid resolution, and reflects the characteristic size of the R-T fingers at a given time. (4) Secondary Kelvin-Helmholtz instabilities generate vortex rings and ring-structured magnetic fields. However, the stretching of field lines by R-T fingers is the dominant amplification mechanism. (5) The final structures are very sensitive to the initial magnetic field and numerical resolution. (6) The magnetic field component along the gravity vector dominates as the instabilities grow. This dominance is stronger in three dimensions than in two dimensions, but it becomes less dominant as the resolution increases. (7) Higher resolution produces a greater total magnetic energy and a smaller total kinetic energy.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
- Magnetic fields
- Methods: numerical