High-Performance Partially Cavitating Hydrofoils

Abstract

Partial cavitation reduces hydrofoil wetted area and friction, but usually with a significant drag penalty associated with unsteady cavity dynamics. A design concept for a high-performance partially cavitating hydrofoil that centers on the suppression of these oscillations by tuning the local pressure gradient in the region of cavity closure is described. The design algorithm is based on ideal fluid theory. An example of this design is the OK-2003 hydrofoil, which is derived from the NACA-0015 geometry. The concept is verified through water tunnel experiments. It is found that under partial cavitation, a two-dimensional hydrofoil exhibits up to a 100% increase in the lift-to-drag ratio compared to its noncavitating conditions. The substantial increase in this ratio relative to the ratio exhibited by the initial NACA-0015 hydrofoil remains significant within a 3 deg range of angle of attack and under a variation of cavitation number of about ±0.2. It was also found that this new hydrofoil design reduces hydrodynamic force pulsations under partially cavitating conditions to operational levels typical of noncavitating flow. In order to further verify the design benefits, the effects of cross flow have been studied with a swept hydrofoil of the same cross section. It was found that outstanding performance of the designed cavitating hydrofoil is retained with 15 deg sweep.