Entropy-based cavitation and primary atomization analysis with a 2D transparent injector
Jean-Bernard Blaisot  1@  , Fakhry Abuzahra  1@  , Akira Sou  2@  , Christophe Dumouchel  1@  
1 : Complexe de recherche interprofessionnel en aérothermochimie
Centre National de la Recherche Scientifique : UMR6614, Institut national des sciences appliquées Rouen Normandie, Université de Rouen Normandie
Site Universitaire du Madrillet, BP 12, 76801 St Etienne du Rouvray Cedex -  France
2 : Kobe University

A transparent scale-up injector with asymmetric incoming flow direction was designed to promote cavitation on mainly one-side of the orifice. This orifice has a rectangular cross-section that provides straightforward optical access to the internal flow. This geometry was designed to study the role of the internal flow, and particularly of the development of cavitation, on the modification of the primary atomization process occurring as soon as the liquid emanates from the injector.
The internal flow is classified into four regimes based on the extent of the cavitation zone; 1- no-cavitation, 2- developing cavitation, 3- super cavitation and 4- partial-hydraulic flip cavitation. Image series of 500 images was recorded for different flow rates belonging to regimes 2-4. Image segmentation is applied to each individual image to identify liquid and vapour phase regions. Based on these segmented images, the mean and rms values of the cavitation extent are determined for each cavitating regime. Furthermore, a more detailed statistical analysis of the cavitation is obtained with the computation of an entropy image, bringing indication on interface between vapour and liquid and on the shed cavitation bubbles.
The liquid jet fragmentation is qualified from the entropy analysis also. The primary atomization is associated with the region in the image where the liquid core is fragmented in detached ligaments and drops. This region is easily identified from the entropy analysis and the primary atomization is quantified through the computation of the area of this region.
In the presence of cavitation, the primary atomization process is altered. The way liquid fragmentation is modified by cavitation is shown to be correlated to the extent of the cavitation zone in the orifice. In this paper we give a quantification of these modifications, clearly visible to the naked eye on the images.


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