Implementation of a passive control system for limiting cavitation around hydrofoils

The performance and the durability of hydraulic systems can be significantly compromised by cavitation. To the aim of delaying cavitation inside turbomachinery, a new passive cavitation control system is proposed in this work. The mentioned system has been applied to a NACA0009 hydrofoil, which accurately reproduces the flow field around real impeller blades. Basically, it consists of slots generating a connection between the suction and the pressure side of the foil. This connection results in a pressure rise close to the leading edge of the foil. Numerical simulations have been performed with the open-source CFD code OpenFOAM and the results have been compared to experimental data available in the literature. The simulations allow to investigate the flow field unsteadiness and the possible flow separation induced by the slots. The passive cavitation control system provides remarkable advantages, i.e., strong reduction of the vapour volume fraction (-93%) accompanied by a reasonable level of loss of performance (lift coefficient reduction equal to -25% and drag coefficient increase equal to +42%). This result is particularly interesting in consideration that the leading edge is only a small part of the entire vane of an impeller.