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Endalew A.M.,Catholic University of Leuven | Debaer C.,Fruit Growing Research Station pcfruit | Rutten N.,Fruit Growing Research Station pcfruit | Vercammen J.,Fruit Growing Research Station pcfruit | And 4 more authors.
Boundary-Layer Meteorology | Year: 2011

The effect of tree foliage on sprayer airflow through pear trees in a fruit orchard was studied and modelled in detail. A new three-dimensional (3-D) computational fluid dynamics model that integrates the 3-D canopy architecture with a local closure model to simulate the effect of the stem and branches and leaves of trees separately on airflow was developed. The model was validated with field observations made in an experimental orchard (pcfruit, Sint-Truiden, Belgium) in spring and summer 2008 and was used to investigate the airflow from three air-assisted orchard sprayers (Condor V, Duoprop and AirJet quatt). Velocity magnitudes were measured before and behind leafless and fully-leafed pear canopies across the row while the operating sprayers are passing along the row, and were compared with the simulations. The simulation results predicted the measured values well with all the local relative errors within 20%. The effect of foliar density on airflow from the three air assisted sprayers was manifested by changing the magnitude and direction of the sprayers' air velocity behind the canopy, especially at the denser regions of the canopy and by changing the pattern of velocity decay horizontally along the jet. The developed methodology will also allow a thorough investigation of atmospheric airflow in canopy structures. © 2010 Springer Science+Business Media B.V.


Endalew A.M.,Catholic University of Leuven | Debaer C.,Fruit Growing Research Station pcfruit | Rutten N.,Fruit Growing Research Station pcfruit | Vercammen J.,Fruit Growing Research Station pcfruit | And 4 more authors.
Agricultural and Forest Meteorology | Year: 2010

Pesticide spray flow from air-assisted orchard sprayer through pear orchard and deposition on different environmental systems were estimated using a new integrated computational fluid dynamics (CFD) approach. The model simulated the complex interactions between wind, air and spray flow from the sprayer with target orchard canopy and the neighbouring environment. The new CFD approach involves the incorporation of the actual 3D canopy architecture into the model to simulate its effect on air and spray flow and deposition of droplets on the branches. Source-sink terms were added to the basic momentum and turbulence equations in a detailed sub-domain created around the branches to represent the effect of leaves. The spray droplets were generated from atomization model and tracked using a Lagrangian particle transport model. A new stochastic deposition model was developed and used to calculate deposition on leaves. The deposition model is a function of leaf optical porosity of the trees, leaf area density, leaf drag coefficient and droplet interception coefficient of the leaves. Two distinct nozzle setups, orchard and boom sprayer setups with ATR brown and TT blue nozzles, respectively, were compared to assess the effect of droplet size distribution on spray flow and deposition. The model results were compared with results from field measurements. For both sprayer setups, the simulation results agreed well with the measurements. The spray proportion above the tree height and behind the trees for the boom sprayer setup was 57.2% and 69.6% more than the orchard sprayer setup according to the simulations and the measurements, respectively. Such a model can be used to improve design features and the calibration of operational parameters of sprayers for better spraying efficiency and reduced environmental impact. © 2010 Elsevier B.V.


Endalew A.M.,Catholic University of Leuven | Debaer C.,Fruit Growing Research Station pcfruit | Rutten N.,Fruit Growing Research Station pcfruit | Vercammen J.,Fruit Growing Research Station pcfruit | And 4 more authors.
Computers and Electronics in Agriculture | Year: 2010

A computational fluid dynamics (CFD) model to simulate airflow from air-assisted orchard sprayers through pear canopies was validated for three different sprayers; single-fan (Condor V), two-fan (Duoprop) and four-fan sprayers (AirJet Quatt). The first two sprayers are widely used in Belgium and the latter one is a new design. Validation experiments were carried out in an experimental orchard (pcfruit, Velm, Belgium) in spring 2008. Ultrasonic anemometers were used to measure the time-averaged velocity components at different vertical positions before the tree and after the tree when the sprayers were driven through the orchard. The model was able to predict accurately the peak jet velocity, Um from all the sprayers considered at all distances from the sprayer centre and vertical positions. More than 95% of the local relative errors of Um were below 20%. Average relative errors, E, and root mean square errors, ERMS, were all less than 11.04% and 1.68 m s-1, respectively. The regions of high- (up to 18.0 m s-1 upstream) and low (down to 2.8 m s-1 downstream)-air velocity zones for all the sprayers were accurately predicted. The simulation results showed that the Condor V sprayer had a highly disturbed vertical jet velocity profile, especially at higher heights. The Duoprop sprayer had high jet velocities at the two-fan positions and lower jet velocity in between the two fans. Within the canopy height the AirJet Quatt sprayer showed a more uniform distribution of air than the other two sprayers except the minor peaks at the fan positions. These situations were all confirmed by the measurements. © 2009 Elsevier B.V. All rights reserved.


Endalew A.M.,Catholic University of Leuven | Debaer C.,Fruit Growing Research Station pcfruit | Rutten N.,Fruit Growing Research Station pcfruit | Vercammen J.,Fruit Growing Research Station pcfruit | And 4 more authors.
Computers and Electronics in Agriculture | Year: 2010

The current trend in modelling flow phenomena within trees such as in orchards follows the assumption of the space occupied by the trees as a porous and horizontally homogeneous medium to avoid the flow details associated with the individual plants. This being sufficient at a larger field or regional scale much has to be done at a plant scale to analyse the flow details within the plant and its elements especially for sensitive agricultural operations such as spraying. This article presents an integrated 3D computational fluid dynamics (CFD) model of airflow from a two-fan air-assisted cross-flow orchard sprayer through non-leafed orchard pear trees of 3 m average height. In this model the effect of the solid part of the canopy on airflow was modelled by directly introducing the actual 3D architecture of the canopy into the CFD model. The effect of small canopy parts, such as very short and thin branches and flowers that were not incorporated in the geometrical model, on airflow was simulated by introducing source-sink terms in the Reynolds averaged Navier-Stokes (RANS) momentum and k-ε turbulence equations in a sub-domain created around the branches. This model was implemented in a CFD code of ANSYS-CFX-11.0 (ANSYS, Inc., Canonsburg, PA, USA). In this work it was possible to link the real 3D architecture of pear canopy into a CFD code of CFX. The model was able to capture the local effects of the canopy and its parts on wind and sprayer airflow directly by inserting the tree structure into the model which gave realistic results. The model showed that within the injection region of the sprayer there was an average reduction of the jet velocity by 1 m s-1 for a distance of 2.3 m from the sprayer outlet due to the presence of leafless pear canopy. This reduction was variable at different vertical positions due to the difference in the canopy density. Maximal effect of the canopy was observed in the middle height of the trees between 0.25 m and 2.5 m which is the denser region with a bunch of several branches. The maximum velocity difference observed between these two positions was 1.35 m s-1 at 1.75 m height. Thus, regions of high and low air velocity zones of the sprayer due to the variable branch density of the pear tree were predicted. The effects of wind speed and direction on the air jet from the sprayer were investigated using the model. For a cross- (direction of 90°) wind speed of 5 m s-1 there was about 2 m s-1 reduction in the sprayer jet velocity at the jet centre and 0.5 m horizontal shift of the jet centre towards the wind direction. Generally there was a decrease in the jet velocity with increasing cross-wind and decreasing wind direction with respect to the jet direction. © 2009 Elsevier B.V. All rights reserved.

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