Publication Date:
2005-02-25
Description:
Laboratory experiments on stably stratified grid turbulence have suggested that turbulent diffusivity kp can be expressed in terms of a turbulence activity parameter ε/vN2, with different power-law relations appropriate for different levels of ε/vVN2. To further examine the applicability of these findings to both a wider range of the turbulence intensity parameter ε/vN2 and different forcing mechanisms, DNS data of homogeneous sheared stratified turbulence generated by Shih et al. (2000) and Venayagamoorthy et al. (2003) are analysed in this study. Both scalar eddy diffusivity Kp and eddy viscosity Kv are found to be well-correlated with ε/vN2, and three distinct regimes of behaviour depending on the value of ε/vN2 are apparent. In the diffusive regime D, corresponding to low values of ε/vN2 and decaying turbulence, the total diffusivity reverts to the molecular value; in the intermediate regime I, corresponding to 7 〈 ε/vN2 〈 100 and stationary turbulence, diffusivity exhibits a linear relationship with ε/vN2, as predicted by Osborn (1980); finally, in the energetic regime E, corresponding to higher values of ε/vN2 and growing turbulence, the diffusivity scales with (ε/vN2)1/2. The dependence of the flux Richardson number Rf on ε/vN2 explains the shift in power law between regimes I and E. Estimates for the overturning length scale and velocity scales are found for the various ε/vN2 regimes. It is noted that ε/vN2 ∼ Re/Ri ∼ ReFr2, suggesting that such Reynolds-Richardson number or Reynolds-Froude number aggregates are more descriptive of stratified turbulent flow conditions than the conventional reliance on Richardson number alone. © 2005 Cambridge University Press.
Print ISSN:
0022-1120
Electronic ISSN:
1469-7645
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
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