• wind farm;
  • experiment;
  • terrain effects;
  • turbulence;
  • separated flows;
  • laser Doppler


The turbulent flow above a generic terrain model has been investigated in a wind tunnel. The rather large terrain model was split up into a set of smaller modules, which could be combined in various ways, and consisted of features inspired by the mountainous terrain along the Norwegian coastline. Several vertical velocity profiles were measured above each terrain module, using two-component laser Doppler anemometry. The mean velocity, turbulence intensity and power spectrum in the simulated incoming atmospheric boundary layer were similar to wind in coastal areas. The flow above hills with sharp and rounded crests and various inclination angles, followed by a plateau, was compared. Results for a straight slope with a sharp crest was compared with a rounded hill with a similar slope, revealing large discrepancies. Flow above rounded hills was seen to be very advantageous for wind turbines, with increased mean velocities and reduced turbulence intensity, compared with the incoming flow. Separated flow occurred in the case with a sharp crest, resulting in highly increased levels of turbulence. Results from cases with two mountains of different heights are also reported. When the flow separated downstream of the first mountain, the flow above the second was affected to a varying extent, depending on the height of the upstream mountain compared to the one downstream. Copyright © 2008 John Wiley & Sons, Ltd.