Agricultural and Forest Meteorology 100 2000 169–181
Mean and turbulent air flows and microclimatic patterns in an empty greenhouse tunnel
T. Boulard
∗
, S. Wang, R. Haxaire
I.N.R.A. — Unité de Bioclimatologie — Site Agroparc, Domaine Saint Paul, 84914 Avignon Cedex 9, France Received 17 March 1999; received in revised form 27 August 1999; accepted 20 September 1999
Abstract
The turbulent air flow along with patterns of air temperature and humidity transport were studied in a classical ‘Filclair’ tun- nel, situated near Avignon in the south of France. Measurements with three-dimensional sonic anemometers and rapid-response
hygrometers revealed a strong heterogeneity in the windward side of the tunnel. For winds perpendicular to the axis of the tunnel, the air flow exhibited a strong current crossing the tunnel between the windward and leeward openings and moderate
air velocities in the vertical section situated between two consecutive series of openings. The temperature distribution showed a north–south gradient due to the cold air penetration through the vent opening and a vertical gradient above the soil surface
due to solar energy absorption at the soil level. Air water vapour patterns were quite different from air temperature patterns, with ‘humid’ areas only concentrated along the soil surface close to the source of evaporating water. Analysis of the energy
spectra showed that all the locations had similar spectral levels in the dissipation region. ©2000 Elsevier Science B.V. All rights reserved.
Keywords: Greenhouse climate; Ventilation; 3-D Sonic anemometer; Turbulence intensity; Dissipation rate
1. Introduction
Spatial variations in air velocity and microclimate inside greenhouses influence crop growth through
their effects on transpiration and photosynthesis. This heterogeneity is particularly marked in the case of
plastic tunnel houses, the most frequently used de- sign in the Mediterranean basin. This variability leads
growers to practise excess irrigation and fertilisation, as has been observed on lettuce crops in the south of
France de Tourdonnet, 1998. Variations in the wind flow are largely responsible for this heterogeneity;
∗
Corresponding author. Tel.: +33-4-90-31-60-80; fax: +33-4-90-89-98-10.
E-mail address: boulardavignon.inra.fr T. Boulard.
however, given the complexity of turbulent flows in general and the intricate boundary conditions that exist
within greenhouses, it is not surprising that the details of the air flow remain elusive and seldom considered
even in numerical simulations. To date, most experi- mental studies of ventilation in full-scale greenhouses
have employed tracer techniques de Jong, 1990; Fer- nandez and Bailey, 1992; Boulard and Draoui, 1995
that neither allow clear identification of the compo- nents of energy and mass transfer through the vent
openings, nor a detailed information on the air-flow pattern within the structure. More recently, Mistriotis
et al. 1997 have used computational fluid-dynamics techniques to simulate forced convective exchanges in
a greenhouse subject to external winds. Experimental and numerical studies by Boulard et al. 1998 have
0168-192300 – see front matter ©2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 9 2 3 9 9 0 0 1 3 6 - 7
170 T. Boulard et al. Agricultural and Forest Meteorology 100 2000 169–181
investigated the detailed temperature and air-flow patterns under conditions of free convection in a
greenhouse equipped with roof openings. All these numerical studies require further empirical validation
particularly in the case of turbulent characteristics, which represent the most critical factors to take into
account in simulations Mohammadi and Pironneau, 1994.
Further insight into the turbulent air flow and asso- ciated sensible heat exchange in a naturally ventilated
bi-span greenhouse was provided by measurements with an ultrasonic anemometer operated in a horizon-
tal plane at the level of continuous openings Boulard et al., 1997. Similar data is lacking for tunnel-type
greenhouses, a fact that provides the primary motiva- tion for the current study. This paper deals with the
characterisation of mean and turbulent air flows and patterns of air temperature and humidity inside a clas-
sical 8-m wide tunnel house. The tunnel under study was sheltered upwind by other tunnels and oriented
perpendicularly to the dominant wind direction as is usual in this region. Natural ventilation was provided
by means of discontinuous openings placed every 4 m on either side of the tunnel. Such conditions are
common in southern France and in all other Mediter- ranean regions where the use of tunnel houses is
widespread.
The present study builds upon measurements of mean and fluctuating air speeds, and fluctuations in
temperature and humidity to: 1. characterise patterns of air flow and the microcli-
matic heterogeneity in vertical cross sections of a tunnel; and
2. evaluate the mean and turbulence characteristics of air velocity components.
2. Theory
