25 Oct 2021

25 Oct 2021

Review status: this preprint is currently under review for the journal WES.

CFD Studies on Wind Turbine Interactions with the Turbulent Local Flow Field Influenced by Complex Topography and Thermal Stratification

Patrick Letzgus, Giorgia Guma, and Thorsten Lutz Patrick Letzgus et al.
  • Institute of Aerodynamics and Gas Dynamics, University of Stuttgart, Pfaffenwaldring 21, 70563 Stuttgart, Germany

Abstract. This paper shows the results of CFD studies of turbulent flow fields and their effects on a wind turbine in complex terrain. As part of the WINSENT project a research test site comprising four meteorological masts and two research wind turbines is currently being constructed in the Swabian Alps in Southern Germany. This work is an essential part of the research of the Southern German wind energy research cluster WindForS. The terrain site is characterised by a densely forested escarpment and a flat plateau downstream of the slope. The met masts and wind turbines are built on this plateau.

In the first part, high-resolution CFD simulations are performed to separately investigate the effects of the forested escarpment and of thermal stratification on the flow field and on the wind turbine accordingly. In the second part, all the examined effects are combined for a real-life case dated March 2021. There, unstable conditions prevailed and the forest shows low leaf area densities due to the wintertime.

It is shown that atmospheric turbulence, forests, orographies, and thermal stratification must be considered when assessing the impact of wind turbines in complex terrain. All of these effects influence the flow field both at the turbine position as well as in its wake. Turbulent structures of the forest wake cross the rotor plane temporarily and thereby affect the turbine inflow. Moreover, convective conditions and upward flows caused by the orography have an impact on the performance output as inclined flows result in asymmetric torque distributions. The wind turbine wake and the forest wake mix further downstream, resulting in a fast decay of the turbine wake. The paper also describes how the turbulent flow in the wake changes in the presence of thermal stratification.

Patrick Letzgus et al.

Status: open (until 01 Jan 2022)

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Patrick Letzgus et al.

Patrick Letzgus et al.


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Short summary
The research article presents the results of a study of highly resolved numerical simulations of a wind energy test site in complex terrain that is currently under construction in the Swabian Alps in Southern Germany. The numerical results emphasised the importance of considering orography, vegetation, and thermal stratification in numerical simulations to resolve the wind field decently. In this way, the effects on loads, power, and wake of the wind turbine can also be predicted well.