Particle image velocimetry (PIV) has been used to compare between turbulence characteristics just within and above a mature corn canopy and those of a model canopy setup in a wind tunnel (WT). The laboratory normalized mean velocity profile is adjusted using variable mesh screens to match the normalized mean shear of the corn field (CF) data. The smallest resolved scale in the field is about 15 times the Kolmogorov length scale (ηCF ≈ 0.4 mm), whereas in the WT it is 5 times ηWT (ηWT ≈ 0.15 mm). In both cases, the mean velocity and turbulence statistics are consistent with those measured using single point sensors. However, the profiles of normalized Reynolds shear stress in the field and the laboratory differ. Turbulent spectral densities calculated from PIV spatial and time series in the field display an inertial range spanning three decades. In the laboratory due to lower Reynolds numbers, the inertial range shrinks to two decades. Quadrant-Hole analysis is applied to Reynolds shear stress, vorticity magnitude and dissipation rates. In quadrants 1–3, the WT and field conditionally sampled stresses show similar trends. However, a conflicting trend is found in the sweep quadrant. The analysis confirms that sweep and ejections dominate the momentum flux and dissipation rate.
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We would like to thank Mike Embry of the Wye Research and Education Center of the University of Maryland for his help in finding a proper location to conduct the field experiments, and Mac Farms Inc., for generously granting us access to their corn field. We are also grateful to Y. Ronzhes and S. King for their technical expertise in developing and maintaining the equipment, as well as J. Kleissl and M. Parlange for providing us with the sonic anemometer data. This research was funded by the Bio-Complexity Program of the National Science Foundation under grant 0119903. The experiments presented in this paper comply with the current laws of the country in which they were performed.
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