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Dynamos driven by rotating convection in the plane layer geometry are investigated numerically for a range of Ekman number ( $$E$$ ), magnetic Prandtl number ( $Pm$ ) and Rayleigh number ( $Ra$ ). The primary purpose of the investigation is to compare results of the simulations with previously developed asymptotic theory that is applicable in the limit of rapid rotation. We find that all of the simulations are in the quasi-geostrophic regime in which the Coriolis and pressure gradient forces are approximately balanced at leading order, whereas all other forces, including the Lorentz force, act as perturbations. Agreement between simulation output and asymptotic scalings for the energetics, flow speeds, magnetic field amplitude and length scales is found. The transition from large-scale dynamos to small-scale dynamos is well described by the magnetic Reynolds number based on the small convective length scale, $$\widetilde {Rm}$$ , with large-scale dynamos preferred when $$\widetilde {Rm} \lesssim O(1)$$ . The magnitude of the large-scale magnetic field is observed to saturate and become approximately constant with increasing Rayleigh number. Energy spectra show that all length scales present in the flow field and the small-scale magnetic field are consistent with a scaling of $$E^{1/3}$$ , even in the turbulent regime. For a fixed value of $$E$$ , we find that the viscous dissipation length scale is approximately constant over a broad range of $Ra$ ; the ohmic dissipation length scale is approximately constant within the large-scale dynamo regime, but transitions to a $$\widetilde {Rm}^{-1/2}$$ scaling in the small-scale dynamo regime.
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TURBULENT RAYLEIGH-BENARD CONVECTION IN STRONG VERTICAL MAGNETIC FIELD
Direct numerical simulations are applied to study turbulent Rayleigh-Bénard convection in a vertical cylindrical cavity with uniform axial magnetic field. Flows at moderate Hartmann and Grashof numbers are considered. It is found that the flow is dominated by large- scale coherent structures in the form of near wall jets forming a large-scale circulation roll. Increase of Ha from 50 to 100 has an expected effect of suppression on the rate of heat transfer.
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- Award ID(s):
- 1803730
- PAR ID:
- 10104162
- Date Published:
- Journal Name:
- Fundamental and applied MHD. 11th PAMIR international conference
- Volume:
- 1
- Page Range / eLocation ID:
- 1-5
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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