Effects of Ambient Conditions, the Gravity Field, and Struts, on Flows over Ventilated Hydrofoils

摘要

A series of experiments was conducted to determine the effects on foil performance of changes in cavity pressure and submergence depth. With fully-ventilated foils, drag and lift coefficients were found to be proportional to (1 + sigma sub cav), as predicted by theory. For base-ventilated foils a different and unexpected dependence of drag and lift on the cavity cavitation number was observed. Lift and drag on fully ventilated hydrofoils were also found to be almost unaffected by changes in submergence depth over the range of practical interest, as predicted by theory. However, the magnitudes of the measured forces were found to be smaller than predicted values. A simple analysis was made of the possible effects of the gravity field on foil performance. Further support for the idea that the gravity field may exert considerable influence was obtained through a series of tests in which ventilated hydrofoils were operated at both positive and negative angles of attack. Measurements were also made to determine the effects of struts on ventilated hydrofoil cavity contours. Indirectly, these tests also assessed the magnitude of the strut-induced downwash. A considerable downwash was found to exist, having a profound effect on the cavity shape over the hydrofoil. Recent linearized theory on the magnitude of this strut-induced downwash correlates very well with the measurements. (Author)