Experimental Studies of Air Ventilation of Vertical Semi-Submerged Bodies

Experimental studies were conducted to investigate the scale-effect problem associated with the ventilation of vertical, semi-submerged cylindrical rods and streamlined lifting surfaces. Several of the rods were coated with Teflon, a non-wetting material. Two types of ventilation--creeping and flash--have been observed for these shapes. Data for the large-diameter rods can be correlated with the Froude number, whereas uncoated rods of small diameter require consideration of several parameters. The use of Teflon-coated rods improved the Froude number correlation for the rods of small diameter. Ventilation of vertical, lifting struts is primarily a function of velocity, yaw angle, submergence, and foil shape. Ventilation data of two foil shapes at high yaw angles can be correlated with the Froude number based on chord. Ventilation data at low yaw angles have not been successfully analyzed. Some data are presented for the spanwise and chordwise pressure distributions about a surface-piercing dihedral hydrofoil (NACA 0012) at several angles of attack and dihedral angles. Distributions were obtained at subcritical and supercritical velocities. A tendency was noted for the center of pressure to move forward as the measuring section approached the free surface.