Photosynthesis Under Field Conditions. VIII. Analysis of Windspeed Fluctuation Data to Evaluate Turbulent Exchange Within a Corn Crop

Wright, J.L. and Lemon, E.R. (1966) Photosynthesis Under Field Conditions. VIII. Analysis of Windspeed Fluctuation Data to Evaluate Turbulent Exchange Within a Corn Crop. Agronomy Journal. 58:255-261.

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Abstract

Turbulent transfer within a crop of corn was characterized
by an aerodynamic approach. The distributions
of windspeed within an immature and a mature crop
were measured using both cup and heated thermocouple
anemometers. A combination of the statistical and mixing-length
theories was employed to analyze the wind
data for transfer coefficients.

Eulerian time scales of turbulence were calculated from
the windspeed fluctuations of selected 30-second periods
of semi-steady wind. Momentum transfer coefficients were
determined from the scale of turbulence by equating it to
the mixing length and assuming isotropy. The resulting
values were as large as 8,000 cm2 sec-1. The shearing
stress profiles calculated with these values had unrealistically
sharp maximums just below the top of the crop.
This anomaly was considered an artifact of the method
resulting from extreme anisotropy in the turbulent shear
flow.
The K values obtained by the statistical mixing length
method were approximately ten times larger than those
determined by logarithmic profile analysis. The latter
values were considered more nearly correct and were used
as a basis for correcting the other values.
The results showed that the magnitude of turbulent
transfer is several orders of magnitude greater than
molecular diffusion even at levels deep within the crop.
The transfer coefficient showed a marked attenuation
with depth below the top of the corn but remained a
function of windspeed at all heights.

Item Type:	Article
NWISRL Publication Number:	0059
Subjects:	Irrigated crops > Corn / maize Research methodology Mass Import - autoclassified (may be erroneous)
Depositing User:	Dan Stieneke
Date Deposited:	20 Nov 2010 21:52
Last Modified:	13 Jan 2017 18:51
Item ID:	477
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/477