Identification of airfoil polars from uncertain experimental measurements

Abstract. A new method is described to identify the aerodynamic characteristics of blade airfoils directly from operational data of the turbine. Improving on a previously published approach, the present method is based on a new maximum likelihood formulation that includes both errors in the outputs and in the inputs, generalizing the classical error-in-the-outputs only formulation. Since many parameters are necessary to meaningfully represent the behavior of airfoil polars as functions of angle of attack and Reynolds number, the approach uses a singular value decomposition to solve for a reduced set of observable parameters. The new approach is demonstrated by identify high quality polars for small-scale wind turbines used in wind tunnel experiments for wake and wind farm control research.