A Quantitative Comparison of Aeroelastic Computations using Flex5 and Actuator Methods in LES

Actuator disc and actuator line techniques are widely used for modelling wind turbines operating in wind farms. These techniques essentially replace the blade geometry with applied body forces, which reduce the resolved length scales significantly and hence the required grid resolution. This work is a verification of the coupling between the flow solver EllipSys3D and the aeroelastic tool Flex5, through a quantitative comparison of coupled actuator line, coupled actuator disc, and standalone Flex5. Steady state performance predictions, instantaneous reaction to turbulence and damage equivalent load analyses all show a very good agreement between the three methods. Differences can be explained primarily by the higher fidelity modelling of the coupled simulations; this is particularly in regard to the influence of blade flexibility, as the actuators deflect and interact with the modelled flow. Additionally, some overpredictions of loading at the blade tip and root below rated velocity for the actuator methods can be attributed to the Gaussian smearing used to apply the body forces.