Experimental Study and Simulation of Cavitation Shedding in Diesel Engine Nozzle using Proper Orthogonal Decomposition and Large Eddy Simulation

The unsteady cloud cavitation shedding in fuel nozzles greatly influences the flow characteristics and spray break-up of fuel, thereby causing erosion damage. With the application of high-pressure common rail systems in diesel engines, this phenomenon frequently occurs in the nozzle; however, cloud cavitation shedding frequency and its mechanism have yet to be studied in detail. In this study, a visualization experiment and proper orthogonal decomposition (POD) method were used to study the variations in the cavitation shedding frequency and analyze the cavitation flow structure in a 3 mm square nozzle. In addition, large eddy simulation (LES) was performed to explore the causes of cavitation shedding, and the relationship between cavitation and vortices. With the increase of the inlet and outlet pressure differences, and fuel temperatures, the degree of cavitation intensified and the frequency of cavitation cloud shedding gradually decreased. LES demonstrated the relationship between the vortices, and the development, shedding, and collapse of the cavitation clouds. Further, the re-entrant jet mechanism was found to be the main reason for the shedding of cavitation clouds. Through comparative experiments, the fluctuation of the vapor volume fraction in the nozzle hole accurately predicted the regions with stable cavitation, re-entrant jet, cavitation cloud shedding, and collapse. The frequency of cavitation shedding can then be calculated. This study employed an instantaneous POD method based on instantaneous cavitation images, which can distinguish the evolution process and characteristics of cavitation in the nozzle hole of diesel engines.

Automated summary

In this study, a visualization experiment and proper orthogonal decomposition (POD) method were used to study the variations in the cavitation shedding frequency and analyze the cavitation flow structure in a 3 mm square nozzle. Large eddy simulation (LES) was performed to explore the causes of cavitation shedding, and the relationship between cavitation and vortices. The re-entrant jet mechanism was found to be the main reason for the shedding of cavitation clouds.