Control of cavitating flow over a 2D hydrofoil by active mass injection through a slot channel in its surface

We studied cavitating flow over the suction side of a symmetric 2D foil - a scaled-down model of high-pressure hydroturbine guide vanes (GV) - in different cavitation regimes at several attack angles. High-speed imaging was used to analyze spatial patterns and time dynamics of the gas-vapor cavities, as well as for evaluating the characteristic integral parameters. A hydroacoustic pressure transducer was employed to register time-spectra of pressure fluctuations behind the hydrofoil and, thereby, determine dedicated frequencies of unsteady regimes. A PIV technique was applied to measure the velocity fields and its fluctuations, which were compared for the free and forced flow conditions. The active flow control was implemented by means of a continuous liquid supply with different flow rates through a slot channel located in the GV surface at the distaence of 60% of the chord length from the foil leading edge. It was found that the active mass injection does not influence the primary flow upstream of the slot channel position absolutely. At small angles of incidence, the injection flow at velocities in the range between zero to 0.76 of the mean bulk velocity was observed not to practically influence the distributions of turbulent characteristics so that the global difference is only between the free and forced flow conditions. For cavitation-free and cavitation inception cases, the active mass injection was shown to make the flow turbulence structure more developed and the wake past the GV section more intense. However, the active flow control system considered also allows a favorable and efficient flow manipulation, especially at the regimes with developed gas-vapor cavities. Moreover, the active flow management makes it possible to reduce substantially the amplitude or totally suppress the periodic cavity length oscillations and pressure pulsations associated with them.