A Wind Tunnel Study of Airflow through Horticultural Crops: Determination of the Drag Coefficient

Molina-Aiz, F.D.; Valera, D.L.; Martínez, Antonio Jesús Álvarez; Madueño, Adrián Feria

doi:10.1016/j.biosystemseng.2006.01.016

Cited by 87 publications

(52 citation statements)

References 42 publications

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“…Experiments have been conducted using dead vegetation [125], live vegetation [60,78], or artificial vegetation [79,95,126,127]. Suter-Burri et al [60] used coloured sand to visualize spatial patterns of sediment redistribution within grass tussocks, allowing them to relate different canopy densities to their theoretical flow regimes ( Figure 6).…”

Section: Evidence From Wind Tunnel Windbreak and Field Studiesmentioning

confidence: 99%

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

Mayaud

Webb

2017

Land

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Drylands are characterised by patchy vegetation, erodible surfaces and erosive aeolian processes. Empirical and modelling studies have shown that vegetation elements provide drag on the overlying airflow, thus affecting wind velocity profiles and altering erosive dynamics on desert surfaces. However, these dynamics are significantly complicated by a variety of factors, including turbulence, and vegetation porosity and pliability effects. This has resulted in some uncertainty about the effect of vegetation on sediment transport in drylands. Here, we review recent progress in our understanding of the effects of dryland vegetation on wind flow and aeolian sediment transport processes. In particular, wind transport models have played a key role in simplifying aeolian processes in partly vegetated landscapes, but a number of key uncertainties and challenges remain. We identify potential future avenues for research that would help to elucidate the roles of vegetation distribution, geometry and scale in shaping the entrainment, transport and redistribution of wind-blown material at multiple scales. Gaps in our collective knowledge must be addressed through a combination of rigorous field, wind tunnel and modelling experiments.

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Section: Evidence From Wind Tunnel Windbreak and Field Studiesmentioning

confidence: 99%

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

Mayaud

Webb

2017

Land

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“…This device is able to produce airflows of up to 10 m s -1 , and is divided into the following principal parts ( Fig. 1): flow conditioner and contraction, test section, diffuser and fan Molina-Aiz et al, 2006). The experimental device forces a current of air through the porous meshes, allowing measurement of both the air velocity and the pressure drop produced.…”

Section: Wind Tunnel Testsmentioning

confidence: 99%

“…In line with Forchheimer's equation, a second degree polynomial can be used (Miguel et al, 1997;Dierickx, 1998;Muñoz et al, 1999) to adjust the experimental values of pressure drop through the mesh (Molina-Aiz et al, 2006;Valera et al, 2006):…”

Section: Wind Tunnel Testsmentioning

confidence: 99%

“…The experimental device forces a current of air through the porous meshes, allowing measurement of both the air velocity and the pressure drop produced. For the technical characteristics of the wind tunnel, the sensors used to measure air velocity and pressure drop and the different electronic components, see Valera et al (2005 and or Molina-Aiz et al (2006).…”

Section: Wind Tunnel Testsmentioning

confidence: 99%

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Microclimate evaluation of a new design of insect-proof screens in a Mediterranean greenhouse

López-Martínez

Valera

Molina-Aiz

et al. 2014

Span. j. agric. res.

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This work studies natural ventilation in a Mediterranean greenhouse, comparing a new experimental screen of 13×30 threads cm-2 (porosity 39.0%) with a commercial control screen of 10×20 threads cm-2 (porosity 33.5%). In addition, both screens were tested in a wind tunnel to determine the discharge coefficients Cd of the greenhouse side and roof vents, which proved to be 0.16 for the commercial control screen and 0.18 for the experimental screen at both vents. These values represent a theoretical increase of 11% (Cd,φ-10×20 /Cd,φ-13×30 = 0.89) in the natural ventilation capacity of the greenhouse when the experimental screen is used. The greenhouse was divided into two separate sections allowing us to analyze natural ventilation in both sectors simultaneously. Air velocity was measured in the lateral and roof vents with two 3D and six 2D sonic anemometers. Using the commercial control screen there was an average reduction of 16% in ventilation rate, and an average increase of 0.5ºC in the average indoor air temperature, compared to the experimental screen. In addition, the ventilation efficiency ηT was higher with the experimental screen (mean value of 0.9) than with the control (mean value 0.6). We have designed an experimental insect-proof screen (13×30 threads cm-2) with smaller thread diameter, higher thread density, smaller pore size and higher porosity than are used in most commercial meshes. All of these factors promote natural ventilation and improve the greenhouse microclimate.

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“…For instance, the artificial leaves are stationary and are thus unable to interact with the wind, which may be an important factor in forest flows (Finnigan, 2010). Similarly, the ridged branches are unable to streamline to the incident flow which results in a coefficient of drag which is independent of the magnitude of the incident wind speed which is not the case in actual canopies (Molina-Aiz et al 2006). Also, as discussed in Bohm et al (2013), the use of scale models of vegetation in wind tunnels may result in the flow being dominated by viscous drag which will not be representative of full-scale flows.…”

Section: Model Treesmentioning

confidence: 99%

A study on the inclusion of forest canopy morphology data in numerical simulations for the purpose of wind resource assessment

Desmond

Watson

Aubrun

et al. 2014

Journal of Wind Engineering and Industrial Aerodynamics

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A series of numerical simulations of the flow over a forest stand have been conducted using two different turbulence closure models along with various levels of canopy morphology data. Simulations have been validated against Stereoscopic Particle Image Velocimetry measurements from a wind tunnel study using one hundred architectural model trees, the porosities of which have been assessed using a photographic technique.It has been found that an accurate assessment of the porosity of the canopy, and specifically the variability with height, improves simulation quality regardless of the turbulence closure model used or the level of canopy geometry included. The observed flow field and recovery of the wake is in line with characteristic canopy flows published in the literature and it was found that the shear stress transport turbulence model was best able to capture this detail numerically.

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A Wind Tunnel Study of Airflow through Horticultural Crops: Determination of the Drag Coefficient

Cited by 87 publications

References 42 publications

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

Vegetation in Drylands: Effects on Wind Flow and Aeolian Sediment Transport

Microclimate evaluation of a new design of insect-proof screens in a Mediterranean greenhouse

A study on the inclusion of forest canopy morphology data in numerical simulations for the purpose of wind resource assessment

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