Bubble size distribution at early stage of hydrodynamic cloud cavitation

The bubble size distribution (BSD) in hydrodynamic cloud cavitation is poorly understood, in spite of its importance in cavitation erosion and noise. Challenges arise owing to the heterogeneous turbulent flows and high void fraction in the cavitation regime. The use of a fiber optical probe enables us to obtain the BSD in a cavitation cloud. Two distinct power law scalings at the early stage of cloud cavitation are identified. The first generation of bubbles is produced by the fission to the shedding cavitation pocket by large-scale turbulence, whose isotropic part leads to the basic scaling - 10 / 3, while the anisotropic part due to the effect of hydrofoil wall contributes to the deviation. The successive fragmentation of bubbles accompanied with turbulent energy cascade results in the fairly uniform scaling - 4 / 3. The results indicate that turbulence plays a dominant role in bubble breakup at the early stage of cloud cavitation.