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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'Optimising measurement strategies to maximise project value: Is the industry making false economies at the expense of project value?' taking place on Tuesday, 11 March 2014 at 11:15-12:45. The meet-the-authors will take place in the poster area.

Alfredo Peña DTU, Denmark
Co-authors:
Alfredo Peña (1) F P
(1) DTU, Roskilde, Denmark

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Abstract

The behavior of the wind profile and wind turning over large wind turbine operating heights

Introduction

Although it is well known that the wind turns with height and that this can have a strong effect on the performance of particularly large wind turbines, there are only few analytical models that are able to predict the behavior with height of both horizontal wind speed components. Numerical micro and meso-scale models are able to reproduce such behavior but evaluation of their performance is difficult due to the lack of accurate observations.

Approach

We performed a nearly 1-year measurement campaign at Høvsøre, Denmark, which is a coastal farmland over flat terrain. The terrain is also homogeneous within an upstream sector and therefore allows us to analyze vertical profiles of both horizontal wind speed components under different atmospheric stability, turbulence and forcing conditions. The observations were carried out with a long-range wind lidar and sonic anemometers on a met mast. The first 100 m are covered by the sonics and from 100 up to 1200 m the vertical profiles are complemented with the wind lidar measurements.

Main body of abstract

We here present results of the analysis of the combined wind lidar/sonic observations of the two horizontal wind speed components, and thus, of the turning of the wind with emphasis on those heights where large wind turbines (will) operate. The results have been classified into 10 different wind conditions each representing atmospheres with different surface atmospheric stabilities (from very stable up to unstable), wind speeds (10-m values of 5 to 10 m/s), and forcing conditions (geostrophic winds of 5 to 20 m/s), which lead to cases of very large, low and negative wind shears, and large and small variations of wind direction with height. The forcing conditions are derived from outputs from the Weather Research and Forecasting (WRF) model and the observations approach well the derived geostrophic winds close to the boundary-layer height. From the analysis of the forcing conditions we are able to identify nearly barotropic and very baroclinic cases. Baroclinity is observed to strongly influence both the wind shear and turning of the wind.

Conclusion

The observed vertical wind shear and turning of the wind are higher in stable conditions compared to unstable conditions. Under both barotropic and baroclinic conditions, the observations of both horizontal wind speed components approach well the geostrophic winds. Only a low-level jet case shows a different behavior. Backing and veering conditions are well simulated by the WRF model, although the model generally underpredicts the turning of the wind.


Learning objectives
- The audience will observe the capabilities of a wind lidar to observe the two horizontal wind speed components
- The audience will be able to see how much the wind veers and turns in the atmospheric boundary layer
- The audience will observe the ability of WRF to simulate forcing conditions