Velocity Of Water Drops At Simulated Rains.

Different spray nozzles are used frequently to simulate natural rain for soil erosion and chemical transport, particularly phosphorous (P), studies.  Oscillating VeeJet nozzles are used mostly in soil erosion research while constant spray FullJet nozzles are commonly used for P transport.   Several characteristics of the rain nozzles are  well defined in the literature,  however some physical properties such as drop size, shape and fall  velocity of rainfall, that enable to estimate kinetic energy are not well quantified. These information are important in order to estimate erosivity, which is the rain potential to cause disaggregation and transport of soil particles. To measure the velocity and kinetic energy of drops from artificial rains generated by those nozzles, a dynamic system of pluviometers, developed in Brazil was used to obtain the velocity spectrum.   In addition, an optical laser disdrometer, was used to measure and compare the kinetic energy of the nozzles tested.  For Veejet nozzles, when the rain intensity varied from 50 to 100 mm per hour, the drop velocity increased from 3.89 to 3.95 meters per second, according to LASER disdrometer.  Comparatively, at the dynamic system of pluviometers the drop velocity ranged from 3.35 to 3.48 meters per second. For Fulljet nozzles, the average velocity measured by the dynamic system of pluviometers varied from 2.98 to 3.16 m/s while the LASER disdrometer detected average velocities ranging from 2.65 to 2.94 m/s.  The discrepancies might have been caused by small oscillations occurred at central gage of the dynamic pluviometers or even by non-vertical trajectory of rain drops.  Variations in Kinetic Energy are expected to be higher since they are related to the square of rain drop velocity.