Abstract
The intermittent features of the turbulent velocity field within a wheat canopy were investigated by conditional sampling techniques and short-period space-time correlations. The velocity and shear stress profiles had qualitatively quite different forms during periods of high and low winds. Analysis of the relative importance of shear-stress contributions from different quadrants of the uw plane revealed the dominant role of gusts in penetrating the canopy and transferring momentum to it from the boundary layer above. Short-period space-time correlations of velocity indicated that over a significant fraction of the time, periodic velocity fluctuations pervaded the canopy-air layer. It is surmised that while this has only a secondary effect on momentum transfer, it may be of overriding importance in heat and mass transport.
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Abbreviations
- x :
-
streamwise co-ordinate positive downwind
- y :
-
cross-stream co-ordinate
- z :
-
vertical co-ordinate, positive upwards
- ũ:
-
instantaneous streamwise velocity
- \(\tilde v\) :
-
instantaneous cross-stream velocity
- \(\tilde w\) :
-
instantaneous vertical velocity
- \(\tilde p\) :
-
instantaneous pressure
- -:
-
denotes long time average
- =:
-
denotes short time average
- ^:
-
denotes conditional average subscript R denotes reference wire (z = 2.0 m) Other symbols are defined as they are encountered in the text.
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Finnigan, J.J. Turbulence in waving wheat. Boundary-Layer Meteorol 16, 213–236 (1979). https://doi.org/10.1007/BF02350512
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DOI: https://doi.org/10.1007/BF02350512