Modelling Cavitation and Flash Atomization

Cavitation occurs in many engineering configurations such as marine propellers, liquid turbines, injectors and even flash atomization can be considered related to cavitation. Cavitation occurs when the pressure of liquid falls below the vapour pressure. As the vapour pressure depends on temperature, boiling can happen on superheated liquid. Indeed, homogeneous boiling and cavitation are similar phenomena that can be viewed either based on heat transfer or based on pressure changes, which is more linked to dynamics of the flow. Depending on the amount of produced vapour thermal effect can be considered to be negligible or preponderant to characterize the final two-phase flow. To be applicable for atomization, models of cavitation have to be considered both from pressure and thermal point of view. This is because vapour volume fraction can range from few percent to nearly hundred percent in case of phase inversion. For high level of vapour concentration the structure of two-phase flow changes drastically. Models based on isolated spherical bubbles do not represent the interaction that appears around the surface when a phase inversion occurs. The topic of this paper is therefore to discuss a model based on dense liquid-gas turbulent flows where cavitation modelling has been included in an attempt to capture both thermal and pressure effects. This model is derived from ELSA (Eulerian Lagrangian Spray Atomization) model for atomization. The whole mixture is considered globally with two species: the liquid and the gas. An equation of the amount of surface per unit volume helps to represent momentum transfer at the surface in the ELSA model. Based on this approach, modelling proposals will be presented to represent heat and mass transfer in a wide range of conditions to allow a complete description of cavitation in the context of atomization.