A STUDY OF THE HYDROELASTIC INSTABILITIES OF SWEPT SUPERCAVITATING HYDROFOILS
A theoretical study has been made of the flutter and divergence instabilities of cantilevered flexible hydrofoils in a supercavitating flow condition. A two-dimensional, fluid-loading theory is used to define the unsteady hydrodynamic loads acting along the span of a cantilevered lifting surface with or without sweep. The lifting surface has degrees of freedom both in bending and in torsion, each being a function of spanwise position. A Raleigh-Ritz type of flutter analysis, using only the fundamental uncoupled bending and torsion modes, was used to perform the calculations. The effects of varying the elastic and inertial properties, as well as the effects of varying the flow separation point on the hydroelastic instability characteristics, are determined. It is shown that a nonzero sweepback angle is essential for the occurrence of flutter instability for cantilevered foils in the low mass ratio region. Otherwise, divergence becomes the lowest stability boundary. In the low mass ratio range, the theory predicts that the bending motion predominates the flutter mode and that the flutter speed rises as a function of the secant of the sweep angle. The divergence speed increases much more rapidly as a function of increasing sweep angle throughout the entire mass ratio region. It is further shown that only moderate sweepback is required to eliminate divergence instability completely. Viewed as a whole, this study shows that predictions of hydroelastic instabilities in the low mass ratio region are extremely sensitive to small structural parametric variations.
David Taylor Naval Ship R&D CenterBethesda, MD USA 20084
- Liu, Y N
- Caspar, J R
- Publication Date: 1976-1
- Pagination: 72 p.
- TRT Terms: Boundary layer separation; Flutter (Aeronautics); Flutter (Aeronautics); Hydrofoils; Supercavitating hydrofoils; Two dimensional flow
- Subject Areas: Marine Transportation; Vehicles and Equipment;
- Accession Number: 00134621
- Record Type: Publication
- Source Agency: National Technical Information Service
- Report/Paper Numbers: DTNSRDC-4686 R&D Rpt.
- Files: TRIS
- Created Date: Jun 9 1976 12:00AM