Two-scalar turbulent Rayleigh-Bénard convection: Numerical simulations and unifying theory

We conduct direct numerical simulations for turbulent Rayleigh-Bénard (RB) convection, driven simultaneously by two scalar components (say, temperature and concentration) with different molecular diffusivities, and measure the respective fluxes and the Reynolds number. To account for the results, we generalize the Grossmann-Lohse theory for traditional RB convection (Grossmann & Lohse, J. Fluid Mech., vol. 407, 2000, pp. 27-56; Phys. Rev. Lett., vol. 86 (15), 2001, pp. 3316-3319; Stevens et al., J. Fluid Mech., vol. 730, 2013, pp. 295-308) to this two-scalar turbulent convection. Our numerical results suggest that the generalized theory can successfully capture the overall trends for the fluxes of two scalars and the Reynolds number without introducing any new free parameters. In fact, for most of the parameter space explored here, the theory can even predict the absolute values of the fluxes and the Reynolds number with good accuracy. The current study extends the generality of the Grossmann-Lohse theory in the area of buoyancy-driven convection flows.