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 errors in both the outputs and 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 method is demonstrated by identifying high-quality polars for small-scale wind turbines used in wind tunnel experiments for wake and wind farm control research.