Computer Simulation Image (image) American Institute of Physics Caption Instantaneous streamwise velocity magnitudes on three perpendicular planes across a wind turbine array boundary layer, obtained from computer simulation. The dark semicircles denote the positions of the wind turbines and the blue regions behind them denote the meandering wakes. Such simulations have been used to develop a model for wind farm roughness length, from which optimal wind turbine spacings can be deduced. Optimal spacing is found to be about 15 diameters. Credit Johan Meyers at Katholieke Universiteit, Leuven (Belgium), and Charles Meneveau, Johns Hopkins University, Baltimore, MD (USA). Usage Restrictions Reporters may use this image so long as they credit Johan Meyers at Katholieke Universiteit, Leuven (Belgium), and Charles Meneveau, Johns Hopkins University, Baltimore, MD (USA). Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.