(An) experimental study of an autorotating Rotor in a uniform flow

Abstract

The purpose of this thesis is to analyse the autorotating rotor in a uniform flow by experimental method. The resultant force acting on a rotor and its aerodynamic characteristics were measured by pyramidal strain gauge balance and by an on-line microcomputer-based measurement system. For the model rotor, two bladed see-saw rotor mechanism was adopted and two kinds of blade with different airfoil section were used. As the blade length of model rotor was relatively short and the air forces acting on it were not large, the twisting effect on the blade pitch angle was not considered. The aerodynamic characteristics of autorotating rotor is largely governed by its tip speed ratio. The fundamental parameters of rotor except L/D ratio are sensitive to small change in pitch angle. The values of lift and drag coefficient based on free stream velocity and rotor disk area decrease as tip speed ratio increases and, especially, they show abrupt decrease when tip speed ratio is in the lower range. The rotor vibration is closely related to the rotor pitching moment and 20-rotor has somewhat severe vibration in the lower range of tip speed ratio.