Wake and performance measurements on the Lawson-Tancred 17 m horizontal-axis windmill

Existing estimates of the efficiency of clusters of wind turbines are principally based on wake data derived from small-scale wind-tunnel tests. Measurements of the wake at 1D and 2.5D downstream of an intermediate size windmill are described here. Centre-line velocity deficits of 0.74 and 0.44, respectively, are found. Even at 1D the wake profile is closely Gaussian. Limited data on the aerodynamic performance and response of the machine are also presented. The performance coeffincient of the rotor is found to be somewhat less than theoretically predicted. The machine response agrees well with calculated behaviour.