The influence of dissolved gas on the cavitation dynamics within a round nozzle

Cavitation is a phenomenon where vapour bubbles form and collapse due to a drop in static pressure of a liquid below the saturated vapour pressure. Understanding cavitation within internal flow domains is critical as it impacts the performance and service life of fluid systems such as fuel injectors and hydraulic valves. All working fluids that have a liquid-gas interface contain dissolved gas which is known to increase cavitation levels. However, the effects of varying dissolved gas concentrations on the cavity dynamics are not well understood. In this study, we employed high-speed backlit imaging to characterise the cavities within a round nozzle, under inception, intermediate and supercavitation conditions with varying concentrations of dissolved CO 2 . We demonstrated the degree of equivalence between gas concentration and cavitation number on cavity length and discharge coefficient relative to cavitation number, and the unique spectral properties of each. Using spectral analysis, we identified three unique oscillatory modes of the cavity and exit jet. The two lower-frequency modes associated with cavity oscillation were primarily influenced by cavitation number (i.e. pressure). A third higher-frequency mode whose frequency depends on gas concentration was identified, which appears only under supercavitation conditions and has not been previously reported. We propose that this higher-frequency mode is related to a coupling of the attached cavity and the bubbly jet exiting the nozzle. • Cavity lengthens with increasing dissolved gas for constant cavitation numbers. • Intermediate cavity dynamics replicate supercavitation with sufficient dissolved gas. • Supercavitation collapse instabilities are affected by dissolved gas concentration.