Quantitative analysis of the minor deviations in nozzle internal geometry effect on the cavitating flow

Cavitation is an important phenomenon occurred inside the nozzle hole and has a significant influence on the internal and jet flow. The quality of atomization for the liquid engines is depended on the status of liquid flow, so that the complicated cavitating flow inside discharge nozzles has long been concentrated on. Cavitation is sensitive to geometric structure, operation condition and liquid properties. At present, achieving high precision in mass manufacturing and measurement of nozzle orifices on micrometer scales is still very difficult, and minor deviations in nozzle internal geometry caused by manufacturing errors or abrasion are inevitable. These deviations will cause an irregular and more complicated internal morphology of the nozzle structure, so that the circumstances of cavitation and flow field are also diversiform, and thus affect the quality of fuel atomization and engine performance. In this paper, the diameter error, conicality and incline that embody common deviations in nozzle geometry are experimentally investigated using transparent nozzles. The geometry dimensions of tested nozzles were ultra-precise measured by self-developed microhole-measuring system based on a twin FBG (fiber Bragg grating) probe. The internal flows of nozzles were visualized and their hydraulic characterization analyzed. The results indicate that very small differences in geometric structure still have consequences for the obviously different characteristics of cavitating flow.