Multiphase fluid flows,such as sprays and liquid jets,are common processes in Internal Combustion and Gas Turbine engines.Liquid fuel is injected into the combustion chamber and "atomises" into droplets,due to capillary and aerodynamic interactions of the liquid and the surrounding gas.The complete characterization of Atomization at realistic Reynolds and Weber numbers is not possible due to the wide range of scales(from mm to microns)and the need to define a “minimum” computational mesh size that captures the smallest liquid scales.The alternative is to “model” the effects of unresolved scales of liquid-breakup.One approach is to represent the Atomization process through the generation and destruction of the Surface Density(∑-Y and ELSA methods).In order to capture the surface density precisely,both accuracy and mass conservation of the numerical scheme are crucial.A common approach is the coupling of Volume of Fluid with Level Set in CLSVOF,to ensure both improved surface representation and mass conservation.The present work focuses on the numerical study of surface density evolution in simple planar configurations(planar jets).The results show surface density evolution at different momentum ratios: from lower values,characteristic of diesel injectors,to high values,typical of air-blast atomizers in gas turbines.The simulations show the strong correlation between surface density and the formation of ligaments in primary atomization.