Experimental and Theoretical Investigation of Unsteady Supercavitating Hydrofoils of Finite Span.

摘要

Measurements of the forces, moment and cavity pressure on aspect ratio 3 and 5 supercavitating hydrofoils of elliptical planform oscillating in pitch have been obtained at frequencies from 5 to 20 Hz. A region of resonant behavior was found, which corresponds to a natural frequency of the cavity. A thermodynamic analysis of the cavity was performed under the assumptions of a spherical cavity and uniform cavity interior properties. The calculated damped natural frequencies were compared with the results taken from peak oscillatory lift experiments. The damping ratio of the cavity depends upon the partial pressure of air, temperature and cavity size. A numerical method was developed for a supercavitating hydrofoil. The problem of supercavitating hydrofoils of finite span in steady flow was solved numerically and compared with analytical solutions and with experiments. Results of these calculations indicate that this method gave a more accurate prediction of lift and moment coefficients than existing asymptotic theories. The numerical solutions of unsteady hydrofoils of finite span were also compared with experiments. The amplitude of the forces was in good agreement, but the phase differences between theory and experiment was large.