Prediction of raingun application patterns in windy conditions
1993
Richards, P.J. | Weatherhead, E.K.
A semi-empirical model has been developed for predicting the distortion by wind of raingun application patterns. The model can be calibrated from three full-circle wetting pattern field tests and used to predict wetting patterns at any intermediate wind speed and for any sector angle, thus providing data for raingun evaluation. For large sprinklers and rainguns, the water jet induces flow of the surrounding air mass, reducing air resistance and enhancing throw. The model assumes that the distortion of the irrigation pattern by wind is due to the combination of wind drift and range shortening due to disruption of the induced air flow, and that the disruption of the air flow is proportional to the component of the wind velocity perpendicular to the jet near the nozzle. The model was tested against 18 other measured patterns and, except in one case, achieved a reasonable degree of fit with standard deviations of the errors between 1.4 and 3.4 mm/h compared to peak application rates between 23.8 and 30.6 mm/h and a typical standard deviation in the field measurements of 1.55 mm/h due to non-symmetry.
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