Quasi-static magnetoconvection with a tilted magnetic field

Abstract

A numerical study of convection with stress-free boundary conditions in the presence of an imposed magnetic field that is tilted with respect to the direction of gravity is carried out in the limit of small magnetic Reynolds number. The dynamics are investigated over a range of Rayleigh number Ra and Chandrasekhar numbers up to Q = 2 × 10 6 , with the tilt angle between the gravity vector and imposed magnetic field vector fixed at 45 • . For a fixed value of Q and increasing Ra, the convection dynamics can be broadly characterized by three primary flow regimes: (1) quasitwo-dimensional convection rolls near the onset of convection; (2) isolated convection columns aligned with the imposed magnetic field; and (3) unconstrained convection reminiscent of nonmagnetic convection. The influence of varying Q and Ra on the various fields is analyzed. Heat and momentum transport, as characterized by the Nusselt and Reynolds numbers, are quantified and compared with the vertical field case. Ohmic dissipation dominates over viscous dissipation in all cases investigated. Various mean fields are investigated and their scaling behavior is analyzed.Provided Ra is sufficiently large, all investigated values of Q exhibit an inverse kinetic energy cascade that yields strong 'zonal' flows. Relaxation oscillations, as characterized by a quasi-periodic shift in the predominance of either the zonal or non-zonal component of the mean flow, appear for sufficiently large Ra and Q.