Use of Jet-Flapped Hydrofoils as Ship Antipitching Fins

摘要

An analysis is presented to determine the feasibility of using jet flap foils as anti-pitching fins for large ships. The effectiveness of ordinary anti-pitching fins is limited by the occurrence of cavitation. It is shown that the jet flap postpones cavitation until the lift reaches two to three times the no jet value. Boundary layer calculations indicate that cavitation and not separation is the limiting condition for operation of the foil. For an oscillating jet angle, it is shown that at the frequencies associated with wave orbital velocities the forces are quasi-steady and so is the condition for the inception of cavitation. Finally some consideration of the power requirements necessary to operate the jet flap are presented, and it is shown that the power expended to obtain a 25% decrease in pitch is a very small fraction of the total propulsive power available on an aircraft carrier of the Forrestal class. (Author)