Upper bounds on Nusselt number at finite Prandtl number

Antoine Choffrut, Camilla Nobili, and Felix Otto

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Submission date: 19. Dec. 2014
Pages: 61
published in: Journal of differential equations, 260 (2016) 4, p. 3860-3880 
DOI number (of the published article): 10.1016/j.jde.2015.10.051
Bibtex
MSC-Numbers: 35Q30, 35Q35, 76R10, 76E06, 76F99
Keywords and phrases: Rayleigh-B\'enard convection, navier-stokes equations, no-slip boundary condition, finite Prandtl number, Nusselt number, maximal regularity for non-stationary Stokes equat
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Abstract:
We study Rayleigh Bénard convection based on the Boussinesq approximation. We are interested in upper bounds on the Nusselt number Nu, the upwards heat transport, in terms of the Rayleigh number Ra, that characterizes the relative strength of the driving mechanism and the Prandtl number Pr, that characterizes the strength of the inertial effects. We show that, up to logarithmic corrections, the upper bound Nu ≲ Ra of Constantin and Doering (1999) persists as long as Pr ≳ Ra and then crosses over to Nu ≲ Pr⁻Ra. This result improves the one of Wang (2007) by going beyond the perturbative regime Pr ≫ Ra. The proof uses a new way to estimate the transport nonlinearity in the Navier Stokes equations capitalizing on the no-slip boundary condition. It relies on a new Calderón-Zygmund estimate for the non-stationary Stokes equations in L¹ with a borderline Muckenhoupt weight.