Experimental Investigation of the Drag Mechanisms of a Helicopter Rotor in Hovering Flight.

摘要

The present paper describes an experiment in which laser velocimetric methods are employed to investigate the drag mechanisms of a helicopter rotor in hover. Emphasis is on the development of a measurement technique capable of quantifying, the contribution of rotor profile drag to total power required. The scheme devised employs a 2-D LV system to measure the axial and tangential velocity field in the vicinity of the rotor blade. Application of a combined Kutta and Momentum Equation (KME) along a closed contour surrounding the blade section provides a measure of the local sectional normal and shear forces. A detailed survey of the rotor blade's near wake region is then performed in an attempt to directly determine the streamwise, velocity deficit. Integration of the resulting velocity profiles provides a measure of the profile drag. Accuracy of the method is checked by performing measurements at conditions of very low lift and by introducing blade surface modifications which aggravate the profile drag with accompanying comparisons of the effect on sectional and global performance.