Shadowgraphy investigations of high speed water jet atomization into still air

Abstract The present study aims at characterizing the atomization of a water jet which is injected at high velocity into still air thanks to an industrial nozzle particularly used in irrigation. The nozzle diameter is 4.36 mm and exit velocity is about 25 m/s. The droplet size and velocity are analyzed by a double-pulsed shadowgraph imaging technique using a Droplet Tracking Velocimetry (DTV) method and are compared with optical probe measurements. A particular attention is paid to the calibration of the imaging system to define the measurement volume associated with each droplet size and to improve the estimation of droplet diameters. The results of the calibration procedure are then used to estimate the size of non-spherical liquid fragments. Drop size distributions are obtained by image processing as a function of the turbulent scales of the upstream flow, as well as Reynolds and Weber numbers. Preliminary results show that log-normal distributions give the best fit to the experimentally observed drop size distributions. Moreover the ratio of the Mass Median Diameter (MMD) over the Sauter Mean Diameter (SMD) is found to be constant and equal to 1.2, which is in good agreement with previous studies, and yields to a relation between the mean and the standard deviation of lognormal distributions.