Articles
Effect of crop on the wind and shear-stress profiles inside and above an ¿infinite¿ screenhouse
Article number
1154_14
Pages
105 – 110
Language
English
Abstract
The mixing-length model, traditionally used to model wind profiles above extended open fields, has been modified to include a horizontal screen (roof) above the crop.
According to this model, two attributes (parameters) define the aerodynamic properties of the screen: a characteristic resistance (drag) and a characteristic mixing-length.
The former affects the horizontal force on the structure and the latter affects the vertical turbulent transfer across the roof.
Similar parameters (drag and mixing-length) also define the aerodynamic properties of the crop.
In our previous reports described the mixing-length model, we calculated velocity and shear profiles and estimated the screen aerodynamic parameters.
Here, we also estimate the aerodynamic properties of the crop canopy.
Data from two large screenhouses, one covered with a fine ‘insect’ screen and another with a coarse ‘shading’ screen, were used in the analysis.
It turns out that in both cases the crop mixing-length does not limit the size of the turbulent eddies and, therefore, does not affect the turbulent transfer.
Crop drag, however, has some effect.
All things considered, estimating the aerodynamic properties of fine screens from wind and shear profiles does not require detailed and accurate crop information.
According to this model, two attributes (parameters) define the aerodynamic properties of the screen: a characteristic resistance (drag) and a characteristic mixing-length.
The former affects the horizontal force on the structure and the latter affects the vertical turbulent transfer across the roof.
Similar parameters (drag and mixing-length) also define the aerodynamic properties of the crop.
In our previous reports described the mixing-length model, we calculated velocity and shear profiles and estimated the screen aerodynamic parameters.
Here, we also estimate the aerodynamic properties of the crop canopy.
Data from two large screenhouses, one covered with a fine ‘insect’ screen and another with a coarse ‘shading’ screen, were used in the analysis.
It turns out that in both cases the crop mixing-length does not limit the size of the turbulent eddies and, therefore, does not affect the turbulent transfer.
Crop drag, however, has some effect.
All things considered, estimating the aerodynamic properties of fine screens from wind and shear profiles does not require detailed and accurate crop information.
Authors
I. Seginer, M. Pirkner, O. Achiman, Y. Mekhmandarov, J. Tanny
Keywords
large screenhouses, screen properties, crop properties, drag force, mixing-length, momentum-flux, one-dimensional profiles
Online Articles (33)