Flow physics of wind turbines over complex terrain

Wind-turbine measurements over a hilly terrain in the BL wind tunnel at KTH.

Background
With an ever-growing demand of renewable energy, an increasing number of wind farms are built on-shore. Due to this trend, further insight of how the wind-turbine power performance is influenced by the surrounding terrain is desired. In a wind farm, the turbulent wakes behind the front-row turbines cause velocity deficits that reduce the amount of power available to the downstream ones. Furthermore, the wakes behind the turbines interact causing complex flow structures within the wind farm that complicate the energy-yield prediction. On-shore farms are subjected to elevation changes in the terrain that coupled with wind-turbine wake interactions generate additional distortions in the flow field. Only few studies have been conducted in the past regarding these issues, since more focus has been put on offshore wind farms and on the effect of surface roughness.

Aims
The focus of the present project is to study the flow around wind turbines and wind farms in complex-terrain environments in order to gain further insight about the prevailing flow conditions during such situations.

Approaches
Within the project an experimental study of wind-turbine wakes, in the presence of a hilly terrain, has been conducted. This was done in the BL wind tunnel at KTH, using stereoscopic particle image velocimetry (PIV) to study the turbine wake development in planes perpendicular to the free stream. Numerical simulations, using Reynolds averaged Navier-Stokes equations (RANS) and an actuator disc technique, has also been used as a complementary tool to study the wind-turbine wake development. Future wind-tunnel measurements are planned, involving wind farms over flat and complex terrains, from which the large-scale flow structures arising around wind farms will be studied.

Keywords
Complex terrain, wake development, wind-tunnel measurements, wind turbines, wind farms

Research Group

Project leader
Antonio Segalini, STandUP for Wind, KTH Mechanics, Stockholm, Sweden

Other project members

Ann Hyvärinen, STandUP for Wind, KTH Mechanics, Stockholm, Sweden

P. Henrik Alfredsson, STandUP for Wind, KTH Mechanics, Stockholm, Sweden

Links and references

A. Hyvärinen and A. Segalini, ”Effects from complex terrain on wind-turbine performance”, J. Energy Resources Tech. 139 (2017) 051205.

A. Hyvärinen, G. Lacagnina and A. Segalini, ”Experimental study of wind-turbine wakes over hilly terrain”, Submitted for publication, 2017.

A. Hyvärinen and A. Segalini, ”Qualitative comparison of wind-turbine wakes over hilly terrain”, Accepted for publication, J. Phys. Conf. Ser. (2017).

Additional funding (apart from StandUp for Energy)

The present project is funded by the Swedish Research council (VR) under a framework grant for strategic energy research.