Performance of windmills in a closely spaced array

A model based on momentum theory is developed for windmill performance with slipstream interference. Only the two-rotor interference problem is considered. The windmill performance is obtained from momentum theory with the approach velocity of the blanketed part of the rotor assumed to correspond to the fully developed wake velocity of the upstream windmill. It is shown that wake interference between windmills in a closely spaced array strongly degrades system performance, the power output varying cosine-like from interference-free to fully blanketed operation. Performance improvement results from a more favorable distribution of the kinetic energy of the impinging air over each rotor of the array.