The main objective of this project is to define and implement a verified engineering model that accounts for the effects of dynamic inflow (wake related). The model(s) are to be implemented in existing computer models for aero-elastic response and load calculations.
Blade and shaft loads on the Tjaereborg 2 MW turbine were measured for a number of pitching transients and safety stops. Model calculations were conducted for matching conditions; calculated and measured loads are compared and analysed.
The conclusion seems to be warranted that for axial symmetric cases, the dynamic inflow modelling used is capable of describing the flow dynamics sufficiently accurately. The dynamic laod ranges resulting from pitching transients are predicted quite well over a range of tip speed ratios which include high loading, optimal loading and low laoding conditions. Sample calculations showed that unsteady profile aerodynamic effects do not contaminate the measured data to a large extend for the pitching transients considered, so that the measured load overshoot can be attributed to dynamic inflow. Measured and (averaged) calculated time scales appear to be in reasonable agreement in the period shortly after the pitching step, which is the most relevant period. However, the spead in calculated time scales is large and the accuracy in the determination of measured time scales is poor.
There is a need for a better prediction of effects of severe gusts, fast pitching actions and yawed or yawing operation. All these cases are influenced by turbine wake development in time (dynamic inflow). Effects are more pronounced for larger wind turbines, but presently not accounted for by the majority of aero-elastic computer codes for design and certification purposes.
The work will start with the identification of a number of possible approaches for simple engineering models. These models will typically alter the momentum equation of blade element-momentum theory by the addition of a time derivative term. Calculational results of models will be compared both to results of unsteady vortex wake calculations (which is theoretically a correct way of modelling but leads to excessive computer time) and to measurements of real turbines. Part of these measurements are to be performed within this project, on the Esbjerg wind turbine.
The initial workprogramme was extended to yaw misalignment conditions as well as to wind tunnel measurements.
Funding SchemeCSC - Cost-sharing contracts
161 11 Bromma
BS2 0QD Bristol
2628 BL Delft