MEASURED AND SIMULATED UNIFORMITY OF LOW DRIFT NOZZLE SPRINKLERS

Abstract

Field measurements conducted on largescale irrigation systems with fixedplate, low drift nozzle (LDN)sprinklers showed that coefficient of uniformity (CU) values ranged from 70 to over 90. Measured CU values were typicallylower in value for the lower operating pressure systems and for sprinkler packages with wider spacings. Measuredsinglesprinkler distribution patterns were then used in an overlapping sequence with specific sprinkler spacing scenariosto simulate multiplesprinkler distribution patterns for moving systems. Scenarios included sprinkler operating pressures of41, 69, 104, and 138 kPa; sprinkler spacings of 1.83, 2.44, 3.05, and 3.66 m; and nozzle orifice sizes of 4.76 to 7.94 mm witha flow range of 0.16 to 0.77 L/s.<br><br>Simulated patterns and CU values compared well with fieldmeasured patterns and CU values for the respective sprinklersize, spacing, and operating pressure combinations. CU values from simulated patterns were highest for closer sprinklerspacing scenarios (<2.4 m) and higher operating pressures (104 and 138 kPa; still in the low range for sprinkler systems).However, evaporative and wind losses could be higher than with the lower operating pressures, thus reducing the overallapplication efficiency. Based on the spacing, nozzle size, and operating pressure scenarios tested in this research, sprinklerspacing to wetted diameter ratios should not exceed 0.20 in order to achieve coefficients of uniformity in excess of 90 undernowind conditions with fixedplate, LDNtype sprinklers.