Effect of a vertical magnetic field on turbulent Rayleigh-Bénard convection

Abstract

The effect of a vertical uniform magnetic field on Rayleigh-Benard convection is investigated experimentally. We confirm that the threshold of convection is in agreement with linear stability theory up to a Chandrasekhar number Q approximately 4x10(6), higher than in previous experiments. We characterize two convective regimes influenced by MHD effects. In the first one, the Nusselt number Nu proportional to the Rayleigh number Ra, which can be interpreted as a condition of marginal stability for the thermal boundary layer. For higher Ra, a second regime Nu approximately Ra0.43 is obtained.

Large eddy simulations of targeted electromagnetic control of buoyancy-driven turbulent flow in a slender enclosure

“…In this approach, the unresolved motion (in that study modelled by three-equations k − ε − θ 2 closure) covers a significantly larger part of the turbulence spectrum (compared to LES), whereas the large eddy deterministic structure (mean motion) was fully resolved by the numerical mesh. The results of the numerical simulation for strong magnetic field (Ha = 100) showed the appearance of a stable stratified interior, in accordance with experimental observations of Cioni et al [6]. Also, thermal plumes were much more elongated in the vertical direction and horizontal movement of the boundary layers was significantly suppressed for situations with an imposed magnetic field.…”

“…Simulations of turbulent Rayleigh-Bénard convection covered an extended range of Rayleigh (10 5 ≤ Ra ≤ 10 9 ) and Hartmann (0 ≤ Ha ≤ 500) numbers, including longitudinal and perpendicular magnetic field orientations. For transversal magnetic field orientation (aligned with vertical direction) simulations showed good agreement with integral heat transfer suppression observed experimentally by Burr and Müller [3] and Cioni et al [6]. For longitudinal magnetic field orientation (aligned with span-wise direction), a distinct two-dimensional flow reorganisation was observed.…”

“…In contrast to the situation where a uniform vertical magnetic field is imposed over the entire enclosure height and resulting vertical temperature profiles showed the appearance of a stable Fig. 9 The contours of the resolved turbulent kinetic energy and stream-traces in the central horizontal plane z/H = 0.5 for strong electric current of I = 10 A: left-2-magnets configuration, right-3-magnets configuration, Ra = 10 7 , Pr = 7 stratified central region (as observed in Hanjalić and Kenjereš [12,13] as well as in Cioni et al [6]), for the local electromagnetic forcing an unstable stratification is present over the entire enclosure height. An interesting shift towards higher temperature values is observed for higher intensities of applied DC currents.…”

“…Cioni et al [6] investigated the effects of a vertical uniform magnetic field on Rayleigh-Bénard convection in a cylindrical geometry. A liquid metal (mercury) was used as the working fluid because of its high electric conductivity.…”

Effects of a small magnetic field on homoclinic bifurcations in a low-Prandtl-number fluid

“…Thermal convection in a thin fluid layer in the presence of a uniform magnetic field, also known as RayleighBénard (RB) magnetoconvection, has been studied both experimentally [18][19][20][21][22][23][24][25] and theoretically [26][27][28][29][30][31][32][33][34] . The study of RB magnetoconvection is useful for geophysical as well as for astrophysical problems [35][36][37] .…”