Detailed calibration of eddy viscosity turbulence models for incipient cavitating flow predictions in asymmetrical nozzel of injectors/atomizers
Date
2019-11-01
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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.
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Keywords
Cavitation, Injectors, Atomizers, Turbulence, Eddy viscosity models, Validation/Calibration.
Citation
Mecánica Computacional Vol XXXVII
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