Development of Attached Cavitation at Very Low Reynolds Numbers from Partial to Super-Cavitation

Florent Ravelet,Sofiane Khelladi,Christophe Sarraf,Kilian Croci,Farid Bakir,Amélie Danlos

doi:10.3390/app10207350

Abstract

The present study focuses on the inception, the growth, and the potential unsteady dynamics of attached vapor cavities into laminar separation bubbles. A viscous silicon oil has been used in a Venturi geometry to explore the flow for Reynolds numbers ranging from Re=800 to Re=2000. Special care has been taken to extract the maximum amount of dissolved air. At the lowest Reynolds numbers the cavities are steady and grow regularly with decreasing ambient pressure. A transition takes place between Re=1200 and Re=1400 for which different dynamical regimes are identified: a steady regime for tiny cavities, a periodical regime of attached cavity shrinking characterized by a very small Strouhal number for cavities of intermediate sizes, the bursting of aperiodical cavitational vortices which further lower the pressure, and finally steady super-cavitating sheets observed at the lowest of pressures. The growth of the cavity with the decrease of the cavitation number also becomes steeper. This scenario is then well established and similar for Reynolds numbers between Re=1400 and Re=2000.

Highlights

The presence of small separation bubbles close to the leading edge of a profile or to the summit of a wedge provides favorable conditions for the attachment of vaporous cavities when lowering the absolute pressure
Four different regimes have been observed: type-1 small cavities that are almost steady, type-2 periodically shrinking cavities of intermediate sizes, type-3 vortex bursting with no clear period and type-4 supercavities
For Re 6 1000, the background flow is steady and laminar and the cavitating flow gives rise to steady attached cavities whose length slowly increases with a decrease of the cavitation number

Summary

Introduction

The presence of small separation bubbles close to the leading edge of a profile or to the summit of a wedge provides favorable conditions for the attachment of vaporous cavities when lowering the absolute pressure. The fundamentals of sheet cavitation inception can be found for instance in the classical books of C. E. Brennen [1] or J.-P. The inception of such “sheet” cavitation has been for instance studied in Refs. [3,4,5,6,7] on smooth axi-symmetric bodies, on propellers blades or on foils. A recent review of the different sheet cavitation inception mechanisms can be found in Ref. A recent review of the different sheet cavitation inception mechanisms can be found in Ref. [8]

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Conclusion