6,435 research outputs found

    Double-branched vortex generator

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    In order to assess the suitability of using a double branched vortex generator in parametric studies involving vortex interactions, an experimental study of the main vortex and secondary flows produced by a double branched vortex generator was conducted in a 20-by-40 cm indraft wind tunnel. Measurements of the cross flow velocities were made with a five hole pressure probe from which vorticity contours and vortex parameters were derived. The results showed that the optimum configuration consisted of chord extensions with the absence of a centerbody

    Improved Skin Friction Interferometer

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    An improved system for measuring aerodynamic skin friction which uses a dual-laser-beam oil-film interferometer was developed. Improvements in the optical hardware provided equal signal characteristics for each beam and reduced the cost and complexity of the system by replacing polarization rotation by a mirrored prism for separation of the two signals. An automated, objective, data-reduction procedure was implemented to eliminate tedious manual manipulation of the interferometry data records. The present system was intended for use in two-dimensional, incompressible flows over a smooth, level surface without pressure gradient, but the improvements discussed are not limited to this application

    An experimental study of plane mixing layer development

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    Mean flow and turbulence was measured in the near field of two plane mixing layers in air with a maximum velocity of 21 m/sec. The experimental rig enabled mixing layers of velocity ratios 0 and 0.46 to be generated simultaneously. Gases with both tripped and untripped initial boundary layers were studied. It was found that the two stream layer developed to the self preserving state in a distance much shorter than did the single stream layer which followed accepted criteria for the development distance. The asymptotic levels of the turbulence quantities in the two stream layer and the development of the single stream layer showed agreement with existing data. It is suggested that the two stream mixing layer should provide a better test case for the development of turbulence models and calculation methods than the single stream mixing layer

    Winterbeweidung als Alternative zur Mulch- bzw. Schnittnutzung von Kleegrasschlägen [Winter grazing, an alternative to mulching or mowing of grass clover swards]

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    Literature shows that management factors like the type of defoliation and seed mixture have a strong influence on yield, forage quality and N2-fixation of grass clover mixtures. In comparison to harvesting, grazing is cheaper and for economical reasons a maximum grazing period is aimed. Grazing over winter time can cause irreparable damages to the pasture. This problem is of minor relevance for grass clover grown on arable land in its last production year, which it’s ploughed anyway in the following spring. This study compares different grass clover mixtures concerning yield, forage quality and suitability for winter grazing. Grass clover swards varying with respect to the following experimental factors: I. com-panion grass species (perennial ryegrass (Lolium perenne) vs tall fescue (Festuca arundinacea)) and II. legume species (a. white clover (Trifolium repens), b. red clover (Trifolium pratense) and c. alfalfa (Medicago sativa)) were established for comparison. Tall fescue effected higher total dry matter yields than perennial ryegrass. White clover reached the highest crude protein and energy contents of all tested species. In contrast to this, swards with red clover and alfalfa, showing also the highest sward legume contents, reached higher dry matter and nitrogen yields Plots grazed in different periods over winter showed a clear loss of grazable matter. The highest losses of dry matter which also was coupled with a remarkable decrease in crude protein and energy content was observed in mixtures with alfalfa
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