Unraveling Cloud Cavitation: The Role of Rayleigh-Taylor Instability

In multiphase flows, cavitation is one of the phenomena that are not completely understood, especially cloud cavitation which involves complex fluid dynamics. In cloud cavitation, a sheet of vapor grows to a critical length from a low-pressure region in the flow and this sheet of vapor detaches as a cloud of bubbles to high-pressure regions while a new sheet of vapor forms. This cloud of bubbles violently collapses in the high-pressure regions, thereby causing destruction to the equipment. It is a periodic phenomenon and the interactions between the vapor and liquid are not completely understood. These interactions need further investigation to gain a deeper understanding of how this unsteady phenomenon evolves in real-world applications. There are numerous studies available in literature about different mechanisms responsible for the shedding of the vapor cavity and yet no clear understanding about when a particular mechanism is more dominant than others. Usually, the cavity grows to a maximum length before the shedding process starts. However, the visualizations obtained using a high-speed camera, for venturi geometry with certain flow conditions, show that there is an instability at the top interface, causing the cavity to shed slightly before it grows to a maximum length. The instability in question is hypothesized to be Rayleigh-Taylor Instability and the hypothesis is corroborated with the help of an analytical model.