Abo Bibliothek: Guest
Seventh International Symposium on Turbulence and Shear Flow Phenomena
July, 28-31, 2011, Ottawa Convention Centre, Ottawa, Canada

DOI: 10.1615/TSFP7

SCALE DEPENDENT NATURAL COORDINATES FOR ANISOTROPIC ATMOSPHERIC TURBULENT VARIANCES

pages 1-6
DOI: 10.1615/TSFP7.970
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ABSTRAKT

Current theories of atmospheric turbulence focus on isotropic turbulence, which applies only to the smaller spatial scale/higher frequency temporal scale motions. The larger spatial scale/lower frequency eddies carry more energy and are more active in the transport of scalars and momentum. These larger eddies are anisotropic − the variances at these scales are not the same in all directions.
Although it is natural to use streamwise coordinates or other surface-based coordinate systems in models and field measurements, the turbulent variances and covariances that comprise the Reynolds stress tensor have their own natural coordinate system, which is not usually aligned with commonly-used coordinate systems. This means that the direction of maximum variance, and therefore maximum turbulent transport, is not usually the stream-wise direction, nor is the direction of minimum variance and turbulent transport exactly vertical. Dispersion models often base the degree of spreading on estimates of turbulent variance, so improved knowledge of the variances and covariances will improve the performance of such models.
It is often found in laboratory flows that the Reynolds stress coordinates are rotated 17° around the cross-stream axis with respect to a streamwise, cross-stream, wall normal coordinate system (Hanjalic and Launder, 1972). In the case studied here, the Reynolds stress coordinate angles differ for different scales of motion, but are similar to the 17° value.

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