Anisotropies and universality of buoyancy-dominated turbulent fluctuations: a large-eddy simulation study

Turbulent fluctuations of both velocity and temperature fields, issuing from high resolution large eddy simulations, have been analyzed in convective boundary layers. The numerically simulated flows are strongly anisotropic at large scales: this is due both to the action of buoyancy and to the imposed geostrophic wind. Their relative weight is varied so that one experiment results much more convective than the other. To properly disentangle anisotropic properties, we exploit both standard statistical indicators, like skewness coefficients, and the three-dimensional rotational group decomposition $SO(3)$. Two main conclusions can be drawn. First, despite the strong anisotropies at large scales, isotropy is statistically recovered at scales much smaller than the large ones. Second, relevant statistical indicators of turbulence such as the scaling exponents, of both velocity and temperature fields, are remarkably close for the two experiments. Implications of these findings for the problem of subgrid scale modeling are discussed.