AN ACTUATOR DISC THEORY FOR THE SHED WAKE AT LOW TIP SPEED RATIOS
MASSACHUSETTS INST OF TECH CAMBRIDGE AEROELASTIC AND STRUCTURES RESEARCH LAB
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A model of the flow through a helicopter rotor, suitable for estimating shed wake effects in hovering and at low tip speed rations, is described. The method leads to the same result for the aerodynamic damping of blade bending oscillations as more complex theories. It is shown that the damping of small natural oscillations is to a first order unaffected by tip speed ratio. Interharmonic couplings, arising out of the convection of the shed vorticity parallel to the rotor disc, prove to be quite important, especially if resonance occurs. Also, in the presence of strong interharmonic coupling, the effective lift curve slope cannot be considered as a universal parameter, independent of the harmonic content of the blade motion.
- Fluid Mechanics