An experimental and theoretical investigation of the wake behind a porous disk which simulates the effect of a wind turbine is presented. Modeling of the wake in an environmental wind tunnel is described and experimental results for the three-dimensional model wake flowfield are presented. A three-dimensio nal turbulent flow analysis is developed to deal with prediction of the wake characteristics. The theoretical results are shown to display the experimentally observed features of the wake. I. Introduction T HERE is increasing need for accurate prediction of the interaction of wind turbine generators (WTG's) in arrays, as evidenced by literature published both here1'2 and abroad.3 The problem is the determination of the nature of the wake of a WTG and its development downstream prior to possible interaction with another WTG in the array. This is a case of relaxation of a wake in a turbulent shear flow, which is an important basic problem in fluid mechanics and, as such, deserves attention and study. Field tests are being carried out both here and abroad, but such approaches are expensive, difficult to carry out, and by their nature are incapable of being completely controlled. The lack of control contributes to the difficulty of interpreting such experiments and to the hazards of extrapolating from such results. To alleviate this problem it seems important to carry out a coupled experimental and theoretical program on laboratoryscale model wakes for the following reasons: First, such a laboratory investigation would provide information concerning model turbine wake characteristics over a wide range of controlled upstream conditions. Second, wake information thus obtained would be of value for checking the observations of actual wake characteristics and the predictions of various models to be developed in and for projected large-scale programs. Third, a relatively inexpensive tool for continuing assessment of wind turbine flowfields would be in hand. An exploratory investigation of laboratory-sc ale simulated WTG wakes has been carried out by Sforza et al.4 Results of that study are included here for completeness. Other studies have concentrated primarily on the overall effects of clusters of WTG's on global performance rather than on the detailed fluid dynamics of the wake re-energization process, i.e., Refs. 5-25. The objective of the present investigation is to establish the fluid dynamic processes occurring in the development of the flow in the wake, to determine the importance of some of the various simulated atmospheric boundary-layer characteristics on the flow, and to develop a reasonably accurate prediction method for the calculation of the simulated wake flowfield.