Articles
AIRFLOW AND TURBULENCE IN A BANANA SCREENHOUSE
Article number
719_72
Pages
623 – 630
Language
English
Abstract
This paper presents measurements and analysis of airflow patterns,
turbulence characteristics and ventilation in a commercial flat-roof screenhouse in
which a banana crop was grown.
The screenhouse was a rectangle, 352 × 228 × 6 m
high, covered with transparent, 15% woven shading screen.
An eddy covariance
(EC) system was deployed within the screenhouse, 186 m south and 128 m east of its
northwest corner to measure evapotranspiration.
A three-dimensional sonic
anemometer was deployed within the screenhouse near the EC system.
Canopy
height during the measurement period averaged 4.2 m and the anemometer was
installed 5 m above ground.
Internal temperature and humidity were measured near
the anemometer by three aspirated psychrometers, shielded from direct solar
radiation, at heights of 1.5, 3 and 5 m above ground level.
External meteorological
conditions were measured by a standard meteorological station located outside the
screenhouse, about 150 m to the east.
A good correlation was found between inside
air velocity (uint) and outside wind speed (uext). As expected, the inside air velocity
was significantly lower than outside wind speed, the relation being uint=0.27uext – 0.11
(R² = 0.89). Most of the time, airflow directions inside and outside were similar but
during a few events, for southern external wind the airflow inside was northern.
Friction velocity calculated using the measured wind components inside the
screenhouse, u*meas, is compared with the one modelled through the logarithmic wind
profile, under neutral stability, u*mod. The relation between the two was
u*mod=1.02xu*meas+ 0.11 (R² = 0.77), suggesting that the logarithmic wind profile
model is approximately valid.
Average turbulence intensity is 0.49 with a standard
deviation of 0.12 suggesting that on average, Taylor’s hypothesis is marginally
satisfied.
Air exchange rate, Xs, estimated through the vapour balance technique,
increased with external wind speed, as expected, and followed the relation: Xs =
2.39uext + 17.82 (R² = 0.36).
turbulence characteristics and ventilation in a commercial flat-roof screenhouse in
which a banana crop was grown.
The screenhouse was a rectangle, 352 × 228 × 6 m
high, covered with transparent, 15% woven shading screen.
An eddy covariance
(EC) system was deployed within the screenhouse, 186 m south and 128 m east of its
northwest corner to measure evapotranspiration.
A three-dimensional sonic
anemometer was deployed within the screenhouse near the EC system.
Canopy
height during the measurement period averaged 4.2 m and the anemometer was
installed 5 m above ground.
Internal temperature and humidity were measured near
the anemometer by three aspirated psychrometers, shielded from direct solar
radiation, at heights of 1.5, 3 and 5 m above ground level.
External meteorological
conditions were measured by a standard meteorological station located outside the
screenhouse, about 150 m to the east.
A good correlation was found between inside
air velocity (uint) and outside wind speed (uext). As expected, the inside air velocity
was significantly lower than outside wind speed, the relation being uint=0.27uext – 0.11
(R² = 0.89). Most of the time, airflow directions inside and outside were similar but
during a few events, for southern external wind the airflow inside was northern.
Friction velocity calculated using the measured wind components inside the
screenhouse, u*meas, is compared with the one modelled through the logarithmic wind
profile, under neutral stability, u*mod. The relation between the two was
u*mod=1.02xu*meas+ 0.11 (R² = 0.77), suggesting that the logarithmic wind profile
model is approximately valid.
Average turbulence intensity is 0.49 with a standard
deviation of 0.12 suggesting that on average, Taylor’s hypothesis is marginally
satisfied.
Air exchange rate, Xs, estimated through the vapour balance technique,
increased with external wind speed, as expected, and followed the relation: Xs =
2.39uext + 17.82 (R² = 0.36).
Publication
Authors
J. Tanny, S. Cohen, A. Grava, L. Haijun
Keywords
Wind speed, airflow direction, friction velocity, turbulence intensity, air
Online Articles (73)