Original paper
Wind observations from a forested hill: Relating turbulence statistics to surface characteristics in hilly and patchy terrain
Pauscher, Lukas; Callies, Doron; Klaas, Tobias; Foken, Thomas
Meteorologische Zeitschrift Vol. 27 No. 1 (2018), p. 43 - 57
84 references
published: Jan 29, 2018
published online: Dec 1, 2017
manuscript accepted: Aug 9, 2017
manuscript revision received: Aug 7, 2017
manuscript revision requested: May 27, 2017
manuscript received: Apr 17, 2017
Open Access (paper may be downloaded free of charge)
Abstract
This study investigates turbulence characteristics as observed at a 200 m tall mast at a hilly and complex site. It thereby concentrates on turbulence statistics, which are important for the site suitability analysis of a wind turbine. The directional variations in terrain are clearly reflected in the observed turbulence intensities and drag. Integral turbulence statistics showed some variations from their typical flat terrain values. Footprint modelling was used to model the area of effect and to relate the observed turbulence characteristics to the ruggedness and roughness within the estimated fetch area. Among the investigated turbulence quantities, the normalised standard deviation of the wind velocity along the streamlines showed the highest correlation with the effective roughness and ruggedness within the footprint followed by the normalised friction velocity and normalised standard deviation of the vertical wind speed. A differentiation between the effects of roughness and ruggedness was not possible, as forest cover and complex orography are highly correlated at the investigated site. An analysis of turbulence intensity by wind speed indicated a strong influence of atmospheric stability. Stable conditions lead to an overall reduction in turbulence intensity for a wind speed range between approx. 6–12 m s−1 when compared to neutral stratification. The variance of the horizontal wind speed strongly varied over the height range which is typical for a modern wind turbine and was in the order of the differences between different standard turbulence classes for wind turbines.
Keywords
wind energy • turbulence intensity • footprint • complex terrain • ruggedness • design wind conditions