Purpose Understanding the interaction of turbulence and cavitation is an essential step towards better controlling the cavitation phenomenon. The purpose of this paper is to bring out the efficacy of different modelling approaches to predict turbulence and cavitation-induced phase changes. Design/methodology/approach This paper compares the dynamic cavitation (DCM) and Schnerr–Sauer models. Also, the effects of different modelling methods for turbulence, unsteady Reynolds-averaged Navier–Stokes (URANS) and detached eddy simulations (DES) are also brought out. Numerical predictions of internal flow through a venturi are compared with experimental results from the literature. Findings The improved predictive capability of cavitating structures by DCM is brought out clearly. The temporal variation of the cavity size and velocity illustrates the involvement of re-entrant jet in cavity shedding. From the vapour fraction contours and the attached cavity length, it is found that the formation of the re-entrant jet is stronger in DES results compared with that by URANS. Variation of pressure, velocity, void fraction and the mass transfer rate at cavity shedding and collapse regions are presented. Wavelet analysis is used to capture the shedding frequency and also the corresponding occurrence of features of cavity collapse. Originality/value Based on the performance, computational time and resource requirements, this paper shows that the combination of DES and DCM is the most suitable option for predicting turbulent-cavitating flows.
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 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 studied in the present work because in the past, these two venturi geometries (with and without throat) have produced contradictory results with respect to 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, namely 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 employed to bring out underlying flow physics. From these analyses, it was shown that, for the venturi with 23 mm throat length, condensation shock is followed by the re-entrant jet as cavitation number is reduced while reverse order is seen for venturi with zero throat length. Simulations of unsteady, non-cavitating, turbulent flow through these venturis show that this difference in the order of predominance of the two mechanisms can be explained by the product of cavity thickness (approximated by boundary layer height) and average pressure gradient value.
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