A new coupled modelling framework for turbine inflow generation: mesoscale-synthetic turbulence

Abstract

At the mercy of strong winds, high wind shear, unstable boundary layer and anomalous atmospheric conditions, stands a wind turbine designed to produce sustainable power under harsh conditions. The field of wind energy is a promising prospect for a sustainable future. Diverse research towards the improvement of a wind turbine’s capability and cost is currently the focus of the wind energy industry. With higher wind turbines being designed every day, various challenges and limitations of the current state-of-the-art surface; anomalous atmospheric conditions, structural integrity and cost.
The goal of this thesis is to extend the approach to design a site-specific wind turbine considering an anomalous atmospheric condition. By coupling a mesoscale model with a stochastic turbulence function, a wind field capable of depicting a particular atmospheric condition is created. Using an aeroelastic solver the resulting loads on a wind turbine can be simulated. The methodology uses Weather, Research and Forecasting (WRF) model to re-create an event of low-level jet identified at the met mast of FINO-1, off coast Germany. The wind profile is coupled with a stochastic turbulence function designed at FINO-1 to be used as wind field for the aeroelastic solver, FAST.
A literature survey identified a multitude of approaches used for simulating a low-level jet and analyse the loads on a wind turbine, the majority of which indicate high computational costs and contrived re-creations of the event. Thus, the challenge was to identify a near-realistic event creation with low computational costs. Therefore, coupling a low-resolution mesoscale model to create the event with a site-specific stochastic turbulence function is used to analyse loads on a wind turbine.
Meteorological data analysis at FINO-1 led to the identification of three case studies of low-level jets under varied stability conditions of the atmosphere. The case studies are compared with the International Electrotechnical Commission (IEC) standard’s, IEC – 61400 – Ed3; IEC Kaimal and IEC Great Planes Low Level Jet (GPLLJ) spectrum. For cases with high stability, on an average proposed model predicts 21% higher stress on blade root and 27% higher at the tower top and base in comparison to IEC GPLLJ and 15% and 30% lower in comparison to IEC Kaimal, respectively. Similarly, under unstable conditions, proposed model predicts similar loads on the blade root, 7% lower loads at the tower top and base in comparison to IEC GPLLJ and 30% higher loads for blade root and tower top and base in comparison to IEC Kaimal. Comparing these results with literature on high stability loading higher loads are expected under these conditions.
Concluding, this project developed a model framework to analyse anomalous atmospheric phenomena on a wind turbine specific to a site with low computational costs. While the capabilities of the model have been successfully showcased, only a partial validation on a benchmark case has been carried out. Therefore, going forward a full physical validation of the model for its accuracy for its target applications is recommended.