Limitations of Froude's Actuator Disc Concept

摘要

The question of whether the actuator disc including edge forces is a betterrepresentation of the action of conventional helicopter or wind turbine rotors than Froude's mathematical model is addressed. The load on the chordwise bound vorticity of the rotor blade is shown not to perform work, which conflicts with Froude's assumption of the load converting power being equal to the total load. An experiment on a model rotor in hover shows the load converting power to be smaller than the total load on the rotor. It is concluded that the addition of edge forces to Froude's concept improves the performance prediction for rotors significantly, although discrepancies between prediction and measurement remain. The actuator disc itself is addressed and the question of whether the edge forces are an inherent part of the load instead of merely an addition to Froude's concept is addressed numerically and analytically to improve the representation of real rotors. A nonlinear viscous finite element calculation is set up for the flow of a two dimensional actuator strip with a smooth load distribution.