Cloud cavitation, both in external and internal flow fields, has been an active field of research because of its different harmful effects like noise, vibration, and material damage in several applications. In the present work, the same is studied experimentally and numerically using venturi geometries. Venturi geometry was selected because of its diverse applications. The two venturi geometries chosen are nearly identical in all respect except the throat length. The influence of throat length is examined in this study because previously, these two venturi geometries (with and without throat) produced contradictory results in terms of the underlying mechanisms of cavity shedding, namely, re-entrant jets and condensation shocks observed at different cavitation numbers. Different diagnostic strategies were adopted to characterize cavitation events viz., sound pressure level, dynamic pressure fluctuations and high-speed imaging. High-speed images were studied to obtain mean cavity length. Proper orthogonal decomposition (POD) along with wavelet analysis, was also employed. From these analyses, it was shown that for the venturi with 23 mm throat length, the condensation shock is followed by the re-entrant jet as cavitation number is reduced, while reverse is seen for venturi with zero throat length. Simulations of unsteady turbulent-cavitating flow is an essential step to further understand the physics involved. Based on the performance, computational time and resource requirements, the combination of detached eddy simulation (DES) and dynamic cavitation model (DCM) is found to be an efficient tool for predicting turbulent-cavitating flows. The numerical results of the attached cavity length and frequency shedding exibits extremely good accuracy. Thereby, it is shown that the order of predominance of the two mechanisms can be explained by the function of the product of the maximum adverse pressure gradient and the ratio of cavity thickness to re-entrant jet thickness.
KEY WORDS: Cloud cavitation, Venturi geometry, Re-entrant jet, Condensation shock, Proper orthogonal decomposition (POD), Turbulent, Detached eddy simulation (DES), Dynamic cavitation model (DCM).