SIMULATION OF WIND-DISTORTED SPRINKLER PATTERNS

Single-sprinkler wind-distorted distribution patterns are simulated utilizing drop trajectory computations, and compared with measured patterns. It is found that the exact formulation of the drag coefficient of single drops is not critical for applications focusing on water distribution. A drag correction factor, k is introduced to account for the effect of the incidence angle between drag force and orientation of a jet segment. The agreement between measured and computed patterns improves considerably when the proper value of k has been used. Three measures of similarity of computed to measured single patterns are put forth. The most comprehensive measure, denoted by sigma, is a normalized sum of squares of differences between the measured and computed local application rates. The values of k that produce the best agreement in terms of sigma seem to be an increasing function of the range of a sprinkler. Single patterns computed with the best values of k were used to calculate uniformity coefficients for a realistic spacing of the medium-pressure sprinklers under consideration. The results suggest that the computational method can be used to forecast, with an error of only a few percent, the uniformity of application under wind speeds as high as 8 m/s. Considering the effort involved in field measurements, this seems a viable alternative.