The Aerodynamic Efficiency of Windmills

Abstract

SummaryThe paper reproduces the results of an earlier report on the vortex theory of windmills and follows that theory through to establish the aerodynamic design procedure for a horizontal axis windmill. The results are shown to differ considerably from those given in a recent paper by Griffith and the differences are explained. The main conclusion is that, when full allowance is made for the drag of the blades, hub and tip losses, and losses due to interference with the support tower, the power output coefficient or efficiency of a horizontal axis windmill cannot exceed 30 to 35 per cent, as compared to an ideal efficiency of 59 per cent.