Flutter and Cavity-Induced Oscillation of a Two-Degree-Of-Freedom Hydrofoil in Two-Dimensional Cavitating Flow

摘要

Two hydrofoil flutter tests were performed using a two-degree-of-freedom, semiwedge hydrofoil in two-dimensional cavitating flow. In the first test, conducted in the high-speed towing basin, four distinct cavity lengths were tested. Flutter occurred for cavities 1/2 and several chords in length. Cavity-induced oscillations may have occurred for 1-chord cavities, but no oscillations were observed for 2-chord cavities. The flutter results are compared with flutter boundaries predicted by partially cavitating and supercavitating flutter theories. It is concluded that the experimental flutter results do not disagree with the predicted values. In the second test, conducted in the 24-in. variable-pressure water tunnel, cavity lengths were varied from 0 to 3 chords. Cavity-induced oscillations were observed for cavities between 0.4 and 1.4 chords in length, but other cavity lengths were free of oscillation. The oscillations are discussed in terms of forced oscillations of a coupled two-degree-of-freedom elastic system. It is concluded that the cavity-induced oscillations, unlike flutter, are positively damped oscillations. (Author)