Experimental investigation of turbulence within unsteady cavitation

An experimental study based on fast X-ray imaging was performed to investigate the turbulence within unsteady cavitating flows. Cloud cavitation in a small scale Venturi type section, characterized by periodical large-scale oscillations of the sheet cavity, was investigated. The flow was seeded with radio-opaque tracers, and acquisition was performed at the Advanced Photon Source facility of the Argonne National Laboratory. Simultaneous measurements of the liquid and the vapour velocities were obtained by PIV-like image cross-correlations applied to particle and bubble images, while the distribution of the vapour volume fraction was derived from local X-ray absorption. These data were used to determine the distributions of the turbulent kinetic energy k and the turbulent shear stress τ, for several conditions of cavitating flows. The results were then confronted to Reboud’s modification of two-equation eddy viscosity models, which is commonly used to improve the turbulence modelling by reducing the mixture turbulent viscosity in the low void ratio areas of the flow. A nice agreement between the current results and this empirical modification was obtained, explaining a posteriori why Reboud’s correction leads to major improvements in the simulation of cloud cavitation.