Flow visualisation studies on rotating blades.

The effects of radial flows on wind turbine blades are currently being studied by a number of researchers, to shed light on the reasons why blade loads, post stall, are frequently higher than predicted. Flow visualization, using tufts, was used on the blade of a 26 m wind turbine to gain a better understanding of the flow processes. High speed flash photography, synchronized with blade position, has enabled the flow patterns to be explored over a wide range of operating conditions. Location of the separation line was clearly seen as a change in tuft orientation. Correlation of the degree of separation with angle of incidence was achieved using binned incidence data. This in turn led to prediction of the lift curve, using Kirchhoff's method. Results suggest that stall is slightly delayed for this aerofoil, the GA(W)-1, by comparison with two dimensional wind tunnel data.