Investigation for Unsteady Cavitation and Re-entrant Jet on a Foil Section

The mechanism of cloud cavitation generation from a sheet cavity on a foil section has been studied by several researchers. It has been revealed that re-entrant jet cuts the leading edge of sheet cavity and breaks the clear vapour structure into small bubble clusters as cloud cavity. However, the detailed picture of the sheet cavity cut-off phenomenon is still missing. In this study, we carried out experimental observations of sheet-cloud cavity on a NACA0015 foil section using high speed video and hot wires mounted on a foil surface in order to clarify quantitative characteristics of re-entrant jet and its role in sheet cavity cut-off phenomenon.The results of experiments have shown that there were several patterns in the sheet cavity cut-off phenomenon, and that the thickness of re-entrant jet is an important factor.We have also carried out numerical simulations for the same test case. The numerical simulation was performed using a commercial CFD code STAR-CD and the Bubble Two Phase Flow cavitation model implemented in the code. The simulation reproduced unsteady shedding of cloud cavity, although some differences were found in the detailed features of the flow.