Revisiting Bolgiano-Obukhov scaling for moderately stably stratified turbulence

Abstract

According to the celebrated Bolgiano--Obukhov \citep{Bolgiano_1959,Obukhov_1959} phenomenology for moderately stably stratified turbulence, the energy spectrum in the inertial range shows a dual scaling; the kinetic energy follows (i) $\sim k^{-11/5}$ for $k<k_B$, and (ii) $\sim k^{-5/3}$ for $k>k_B$, where $k_B$ is Bolgiano wavenumber. The $k^{-5/3}$ scaling akin to passive scalar turbulence is a direct consequence of the assumption that buoyancy is insignificant for $k>k_B$. We revisit this assumption, and using constancy of kinetic and potential energy fluxes and simple theoretical analysis, we find that $k^{-5/3}$ spectrum is absent. This is because the velocity field at small scales is too weak to establish a constant kinetic energy flux as in passive scalar turbulence. A quantitative condition for the existence of the second regime is also derived in the paper.

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• A revisit of generalized scaling of forced turbulence through flux analysis
• Curvature-based energy spectra revealing flow regime changes in Rayleigh-Bénard convection
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