Development of a potential panel code for unsteady modelling of 2D airfoils in practical applications of large wind turbines

Abstract

The present work is an effort to improve airfoil modelling in wind energy applications, specifically for large wind turbine blades. A new model based on inviscid panel methods with a free vortex wake is proposed for the aerodynamic representation of deforming and moving airfoils in a wide range of operating conditions. Large rotors (above 5MW) operate in a challenging environment in terms of complex inflow conditions and dynamics of the wind turbine. The consequence for the blade sections is a significant variation of the local inflow, leading to unsteady conditions which can largely affect the loads. In order to consider this scenario, the proposed modelling strategy takes into account not only attached flow and static conditions, but also unsteady conditions with flow separation and dynamic stall, for which the present state of the art shows limitations. Some engineering concepts have been included in the formulation in order to account for the effect of the complex conditions. The present model has been implemented in an aerodynamic tool named AdaptFoil2D and an extensive validation has been carried out in order to assess the performance and the suitability of the new model. First, the results of AdaptFoil2D have been compared with experimental data of a cylinder in different flow regimes in order to validate the effect of the flow separation location. Later, static and dynamic experimental tests of the S809 and NACA0015 have been used in the validation of the model for attached and separated flow including dynamic stall. In addition, experimental tests for a NACA64418 with a TE flap have been also used in order to test the ability of the model to deal with changing geometries for active control purposes. Apart from the validation, practical investigations performed with AdaptFoil2D and related to TE flaps for load reduction have been included. The proposed model has demonstrated good performance in the estimation of the aerodynamic loads together with the reasonable computational cost associated to the inviscid approach in comparison to higher fidelity tools.