Turbulent Structure of Cavitating Flow: PIV Measurementsover a Model of Guide Vane of Hydraulic Turbine

The article presents the results of an experimental study of the turbulent structure of flow over a two-dimensional hydrofoil, which is a scaled-down model of guide vane of high-pressure hydraulic turbine. The study was carried out for four regimes of cavitating flow, covering the cases of cavitation-free flow, quasi-steady sheet-vortex cavity with detachments of small-scale cavitation clouds, and unsteady cloud cavitation with periodic separation of the whole attached cavity, formation of large-scale cavitation cloud, and its advection. Distributions of the average velocity, turbulent kinetic energy, and functional shear stresses are given. The transformation of the turbulent structure of the flow over the hydrofoil during transition from the cavitation-free flow to the regime of cloud cavitation is analyzed. Flow regions with non-local characteristics of turbulent transport are detected, where the known semi-empirical gradient-type models used in RANS approaches give qualitatively improper results.