Modelling and validation of wind turbine wake superposition

Abstract

The wind field and, more importantly, the power production change when downstream wind turbines are located in the wake of an upstream wind turbine. Wind farms become larger and therefore the field becomes more complex. Turbines will experience the influence of the wake of multiple wind turbines. The interaction of these wakes can be modelled using different approaches. Using numerical solvers is very computationally costly and accordingly, there is a need for simple engineering wake models which represent the wind field in a good way.
The focus of this MSc Thesis project is to find a superposition method in combination with the Jensen/Park model, which is in good agreement with a representative reference for mixed wakes in reality.
This reference could be either Large Eddy Simulations (LES) or large-scale measurements data from the BEACon campaign, carried out by Ørsted. Comparisons between some datasets showed that more research is needed to identify the discrepancies between the wake fields of both datasets.
Studies have been carried out in literature, but mostly focussing on wind speeds below rated wind speed. Therefore, cases with an inflow wind speed just above and below rated wind speed are considered. The superposition methods looked at are linear superposition, quadratic superposition and the maximum deficit method. The modelling of the wake boundary, rotor averaged wind speed and power are discussed. Some superposition methods are in good agreement with the LES results, but because a uniform profile is modelled, more research is needed to assess if these conclusions also hold for sheared inflow wind profiles.
Apart from examining the combination of superposition methods and the Park wake, a study is also carried out to examine if single LES wakes can be superposed to mimic LES wake fields with multiple wind turbines. Based on the available single LES wakes, there are still essential differences in the results, but these might be overcome if more single LES wakes can be used.
As the proposed superposition methods are not necessarily "true", a preliminary study is carried out in which the superposition method is optimized. This gives an insight in the number of upstream wakes that need to be included and the possible scaling or improvement of the superposition methods.