Mean velocity and temperature profiles in a sheared diabatic turbulent boundary layer

In the atmospheric surface layer, modifications to the logarithmic mean velocity and air temperature profiles induced by thermal stratification or convection are accounted for via stability correction functions Φm and Φh, respectively, that vary with the stability parameter ς. These two stability correction functions are presumed to be universal in shape and independent of the surface characteristics. To date, there is no phenomenological theory that explains all the scaling laws in Φh with ς, how Φh relates to Φmwhy Φh ≤ Φm is consistently reported. To develop such a theory, the recently proposed links between the mean velocity profile and the Kolmogorov spectrum of turbulence, which were previously modified to account for the effects of buoyancy, are generalized here to include the mean air temperature profile. The resulting theory explains the observed scaling laws in Φm and Φh reported in many field and numerical experiments, predicts their behaviors across a wide range of atmospheric stability conditionselucidates why heat is transported more efficiently than momentum in certain stability regimes. In particular, it is shown that the enhancement in heat transport under unstable conditions is linked to a "scale-resonance" between turnover eddies and excursions in the instantaneous air temperature profiles. Excluding this scale-resonance results in the conventional Reynolds analogy with Φm = Φh across all stability conditions. © 2012 American Institute of Physics.

Duke Scholars

Author Gabriel G. Katul Civil and Environmental Engineering