An experimental study of momentum and heavy particle transport in a trellised agricultural canopy

Authors: MILLER, NATHAN - University Of Utah; STOLL, ROB - University Of Utah; Mahaffee, Walter - Walt; Neill, Tara; PARDYJAK, ERIC - University Of Utah

Submitted to: Agriculture and Forest Meterology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2015
Publication Date: 10/15/2015
Citation: Miller, N., Stoll, R., Mahaffee, W.F., Neill, T.M., Pardyjak, E.R. 2015. An experimental study of momentum and heavy particle transport in a trellised agricultural canopy. Agriculture and Forest Meterology. 211-212:100-114.

Interpretive Summary: Fungal pathogens are largely dispersed throughout the environment on air currents. The degree of dispersion is dependent on the velocity and turbulence of the air currents. An understanding of how canopy architecture affects air turbulence will aid in understanding the spatial change in disease develop through time. A series of experiments were conducted where fluorescent microspheres were released as surrogates for fungal spores while recording various meteorological parameters in a commercial vineyard. The particles where trapped down stream at 18 locations and 5 heights (80cm to 5 meters) per location using a custom impaction trap array. These data indicated that the canopy caused channeling of the wind along rows which significantly reduced dispersion of the particles compared to current theory. The data were used to develop a new mathematical model for predicting particle movement down stream when wind was within 22 degrees of the row orientation. Further experiments are needed with a larger and wider sampling array to accurately assess the channeling effects of the row when winds are perpendicular to row orientation. This research will lead to the development of prediction and simulation models that can be used in making management decision or developing and testing hypotheses.

Technical Abstract: Although considerable research has been done on turbulent particle dispersion, little of that work has focused on dispersal patterns near the source or in trellised plant canopies. To study the dispersion characteristics of particles in such canopies, a series of particle release events was performed in a commercial vineyard while local meteorological data were collected. Analysis of the wind velocity data indicated that the majority of the flow within the canopy was channeled parallel to the vine rows regardless of the direction of the mean wind at 2.5 canopy heights, h. Although, this channelling led to significant turning of the mean velocity, profiles of turbulent statistics showed similar behavior to canopy flow profiles in previous studies. The particle release events were conducted using fluorescent microspheres withsimilar physical characteristics to the spores of multiple airborne fungal pathogens of grapes (10-45 µm, 1.0 g/cm3). The microspheres were released from three heights in the canopy and were monitored using a three-dimensional array of impaction traps with locations spanning from 1h to 5h downstream of the source and up to 2.5h high. This provided a relatively high-resolution dataset for the three-dimensional shape of each plume near the source. The shape of the microsphere plumes was strongly impacted by the flow channelling within the canopy. A new model that can account for the wind channelling effects on the plume was developed based on a Gaussian plume model. The new model accurately predicts the microsphere concentrations downwind of the source for above-canopy winds within 22 degrees of the vine row orientation. The new model produced a lower cumulative squared error than a traditional Gaussian plume model for 80% of the plumes when compared to the field data.