COMPRESSIBILITY EFFECTS IN HELICOPTER ROTOR BLADE FLUTTER.
GEORGIA INST OF TECH ATLANTA SCHOOL OF AEROSPACE ENGINEERING
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An analytical investigation of the effect of compressibility on the flutter condition of rotary wings is presented. A two-dimensional model for the helicopter rotor flow field is postulated and used to develop a two-dimensional, unsteady, compressible aerodynamic theory. A kernel function technique is used and the resulting downwash integral equation is solved numerically by collocation using a pressure mode assumption. The resulting aerodynamic coefficients are compared with the results of two other existing theories one incompressible and one compressible and found to agree with these theories when the different flow models used are brought into close agreement. The compressible aerodynamic theory is used in a classical two degree of freedom flutter analysis and a variation of the flutter parameters made to establish their influence under compressible flow conditions. The results indicate that the general trend is for decreasing flutter speed with increasing Mach number. The flutter results obtained using the compressible aerodynamic theory with zero Mach number are also shown to be in excellent agreement with the results obtained using an existing incompressible aerodynamic theory. Author
- Fluid Mechanics