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Field experiments have been conducted in the semiarid southwest region of La Pampa, Argentina, in order to investigate the effect of different types of windbreak on wind characteristics and growth parameters of wheat (Triticum aestivum, Buck Charrua variety) within the sheltered region. Windbreaks decrease wind speed, reducing damage to the crop and improving yield and quality. Sheltering may improve microclimate conditions for plant growth and protects the soil from wind erosion. Aspects of the sheltering ability of four different windbreaks have been tested: single and double row herbaceous (Tritio secale) shelterbelts, and two different artificial wooden fences, with the same overall average porosity, but with different porosity distributions. Mean velocity, turbulence intensity, skewness distributions and spectral and wavelet analysis have been performed in order to characterise the turbulent flow downstream of the different windbreaks. Wheat grain yield and harvest index were compared with adjacent unsheltered plantations. The single and double row shelterbelts enhanced the grain yield and the harvest index of the protected plants. An influence of the turbulent structure on plant growth is suggested by the different response of plants sheltered by the two types of artificial fences.

A NACA 4412 airfoil was tested, in a boundary layer wind tunnel, with the aim to study the effect of a Gurney mini-flap, as an active and passive flow control device submitted to a turbulent flow field. The main objective was the experimental determination of flow pattern characteristics downstream the airfoil in the near wake. The untwisted wing model used for the experiments had 80cm wingspan and 50cm chord, with airfoil NACA 4412. The miniflap was located on the lower surface at a distance, from the trailing edge, of 8%c (c airfoil chord). The Reynolds number, based upon the wing chord and the mean free stream velocity was 326,000 and 489,000. The turbulence intensity was 1.8%. The model was located into the wind tunnel between two panels, in order to assure a close approximation to two-dimensional flow over the model. As an active control device a rotating mini-flaps, geared by an electromechanical system (which rotate to a 30°) was constructed. The wake pattern and pressure values near the trailing edge were measured. The results obtained, for this mechanism, show us that the oscillating mini-flap change the wake flow pattern, alleviating the near wake turbulence and enhancing the vortex pair near the trailing edge at the mini-flap level and below that level, magnifying the effect described first by Liebeck [1]. That effect grows with the oscillating frequency. Additionally, the wake alleviation probably affects also the far wake. All of these facts suggest us to continue with the experiments, trying to measure the pressure distribution around the airfoil in all the cases, obtaining the lift and drag characteristics.

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