Hose reel irrigarion system si the most popular in Europe. To improve the performances of this irrigation system, a good knowledge of the size and spatial distribution of the generated droplets si necessary. The objective of this paper si to investigate the break-up mechanism of water issuing from irrigation nozzle. In order to modelise the atomisation process close to the nozzle, we used an Eulerian desription of single phase to representing the liquid and the gas. This approach si derived from turbumence modelling of non constant density flows. It si based on the calculation of the two quantities which are the "mean liquid mass fraction " and the " mean interfacial area per unit volum in the mixture flow". The knowmedge of these two variables allows the calculation of the liquid drops characteristic size.