Wind-tunnel and field investigation of the effect of local wind direction on speed-up over hills

Measurements of flow past simulated sinusoidal hills were taken in an atmospheric boundary layer wind tunnel (ABLWT) that modeled typical full-scale complex terrain for many wind turbine locations in the Altamont Pass, California, USA. Velocity profiles and speed-up factors for several model hills were determined. All hills modeled had the same height and sinusoidal cross-section, and length-to-width aspect ratios of infinity, four and one. Each of the three models was tested with approach wind directions from 0° to 90°, in 15° increments. It was observed that speed-up can vary significantly depending on the approaching wind direction. The effect of wind direction on speed-up was also investigated using field data from a site in the Altamont Pass. Average speed-up factor was found to vary significantly at the site in time, and as a function of atmospheric stability.