Simulation of wind-farm flows by means of linearized methods

Background
A wind farm is a cluster of several wind turbines placed near each other to reduce the amount of land area used. Due to their large size, numerical modelling of a farm is computationally demanding and standard tools (based on computational fluid dynamics, CFD, for instance) necessitate long computational times (and also high costs) to determine the wind flow and the power output just for one wind direction (from some hours to several days). Consequently, industry has adopted simplified models where the wind-turbine wakes are modelled with some prescribed law with empirical parameters with a computational time of the order of few seconds. However, it has been observed that the latter approach is affected by uncertainties of the order of 25-50%, mostly due to the prescribed model and its empirical parameters. Therefore there is an industrial need to develop new and more accurate models that have reasonable turn-around times and computational costs.

Aims
To develop a new method to simulate wind farms both offshore and onshore (over terrain and forestry) with a fast and accurate model. This could improve the current design chain for wind farms and strategies to properly control farms to increase power production.

Approaches
Linearized methods solve approximate equations that keep only the leading physical flow features, neglecting non-linear interactions (so that the accuracy is expected to be slightly lower than standard CFD). However, the linearized approach enables the use of very fast solution methods, decreasing the computational time of two orders of magnitude. The linearized code ORFEUS has been developed in this spirit by Antonio Segalini at KTH and tested against real wind-farm data, with good results both offshore and onshore. The extension to unsteady turbulent conditions is ongoing, which would provide a tool with even more industrial potential.

Keywords
Wind-farm aerodynamics, Linear methods

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. Segalini (2017), Linearized simulation of flow over wind farms and complex terrains, Phil. Trans R. Soc. A, 375, 20160099

Additional funding (apart from StandUp for Energy)

Vetenskapsrådet och Vindforsk IV