Overstable rotating convection in the presence of a vertical magnetic field

• Published in: Physics of fluids (1994) Vol. 33; no. 3
• Main Authors: Banerjee, Ankan, Ghosh, Manojit, Sharma, Lekha, Pal, Pinaki
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 01.03.2021
• Subjects: Bistability; Direct numerical simulation; Fluid dynamics; Hopf bifurcation; Magnetic fields; Mathematical models; Parameters; Physics; Prandtl number; Rayleigh-Benard convection; Rotation
• ISSN: 1070-6631; 1089-7666
• DOI: 10.1063/5.0035555

Recently, Banerjee et al. [Phys. Rev. E 102, 013107 (2020)] investigated overstable rotating convection in the presence of an external horizontal magnetic field and reported a rich bifurcation structure near the onset. However, the bifurcation structure near the onset of overstable rotating convection in the presence of a vertical magnetic field has not been explored yet. We address the issue here by performing three dimensional direct numerical simulations and low-dimensional modeling of the system using a Rayleigh–Bénard convection model. The control parameters, namely, the Taylor number (Ta), the Chandrasekhar number (Q), and the Prandtl number (Pr) are varied in the ranges 750 ≤ Ta ≤ 10 6 ,   0 < Q ≤ 10 3, and 0 < Pr ≤ 0.5. Our investigation reveals two qualitatively different onset scenarios including bistability (coexistence of subcritical and supercritical convections). Analysis of the low-dimensional model shows that a supercritical Hopf bifurcation is responsible for the supercritical onset and a subcritical pitchfork bifurcation is responsible for the subcritical onset. It is also observed that the appearance of a subcritical convection at the onset has strong dependence on all three control parameters: Ta, Q, and Pr. The scenario of a subcritical convection is found to disappear as Pr is increased for fixed Ta and Q. However, most striking findings of the investigation are that the increment in Ta for fixed Q and Pr opposes the subcritical convection, whereas the increment in Q for fixed Ta and Pr favors it. This is in sharp contrast with the earlier results reported in rotating magnetoconvection.