Vertical profiles of (a) wind speed (<em>u</em>) (ms<sup>−1</sup>), (b) turbulence intensity (TI) (%) from the ZephIR lidar at SW mast on 04/20/2012 at 09:05 (red), 10:45 (blue) and 14:25 (green)

2013-07-16T00:00:00Z (GMT) by Craig M Smith R J Barthelmie S C Pryor
<p><strong>Figure 5.</strong> Vertical profiles of (a) wind speed (<em>u</em>) (ms<sup>−1</sup>), (b) turbulence intensity (TI) (%) from the ZephIR lidar at SW mast on 04/20/2012 at 09:05 (red), 10:45 (blue) and 14:25 (green). Profile times are indicated in figure <a href="http://iopscience.iop.org/1748-9326/8/3/034006/article#erl467625fig4" target="_blank">4</a>(a).</p> <p><strong>Abstract</strong></p> <p>Observations of wakes from individual wind turbines and a multi-megawatt wind energy installation in the Midwestern US indicate that directly downstream of a turbine (at a distance of 190 m, or 2.4 rotor diameters (<em>D</em>)), there is a clear impact on wind speed and turbulence intensity (TI) throughout the rotor swept area. However, at a downwind distance of 2.1 km (26 <em>D</em> downstream of the closest wind turbine) the wake of the whole wind farm is not evident. There is no significant reduction of hub-height wind speed or increase in TI especially during daytime. Thus, in high turbulence regimes even very large wind installations may have only a modest impact on downstream flow fields. No impact is observable in daytime vertical potential temperature gradients at downwind distances of >2 km, but at night the presence of the wind farm does significantly decrease the vertical gradients of potential temperature (though the profile remains stably stratified), largely by increasing the temperature at 2 m.</p>