Detailed calibration of eddy viscosity turbulence models for incipient cavitating flow predictions in asymmetrical nozzel of injectors/atomizers

Abstract

Cavitation in pressure injectors/atomizers strongly affects the liquid/spray jet behavior at its outlet. The type of atomization induced by cavitation allows developing more efficient devices if this cavitation state is controlled. Cavitating flow is related to turbulent and multiphase flows with mass transfer between the liquid and its gaseous phase. It is affected by several factors such as local pressure, local state of the turbulence, non-condensable dissolved gas concentration, nozzle geometry and others. Due to the high speed flow and small spatial and time scales involved, the study of cavitating flows by physical experiments is very expensive. On the other hand, several codes for numerical modeling of cavitating flows have been developed, but turbulent multiphase flow modeling is still a big challenge. Previous works showed that it is possible to capture several of the incipient cavitating flow characteristics performing a careful calibration of the Eddy Viscosity Models in nozzles with symmetrical inlet geometry and with round or square outlet sections. This work extends the study to nozzles with asymmetrical inlet geometry and square outlet section. It was demonstrated in previous works that a careful calibration task should be necessary, because there is a close relation between the cavitation inception/developing condition and the turbulence level in the flow leading to a ‘nonstandard turbulence state’. The spatial distribution and the slow decay of the turbulence level produced by cavitation could be related to some preferred turbulence scales in the process, so cavitating flows should not be modeled as typical turbulence. It is showed that based on the special characteristics of the incipient/slightly developed cavitating flows, a suitable calibration of the turbulence models allows obtaining improved results. These results become competitive when they are compared against ones computed by Large Eddy Simulations which need a lot of computational resources and an appropriate initial solution for running. It was also demonstrated that suppressing by calibration the level of the eddy viscosity in certain zones the vapor fraction predicted rises, provoking the incipient cavitation state in the flow. The obtained conclusions could be useful to improve injectors design using numerical modeling, because the detection of the incipient cavitation flow condition, useful to improve the atomization, could be captured accurately.