On enhancement of hydrofoil performance by partial cavitation

Ventilated cavitation can enhance the performances of various vehicles, including hydrofoil ships. Partial cavitation can reduce the drag coefficients of hydrofoils. For natural partial cavitation of specially designed hydrofoils this reduction is coupled with a significant increase of their lift. The intention to obtain a similar enhancement at smaller vehicle speeds using ventilation of hydrofoil by air looks natural. However, for hydrofoil ventilated cavitation the lift increase at the same cavitation numbers is substantially smaller. The physics of this lift difference is explained here via numerical analysis of the data obtained in water tunnel during experiments with the specially designed hydrofoil OK2003. The unavoidable lift difference is caused by a decrease of medium density downstream of the ventilated cavity due to the air escape from it.