Determination of the Circulation for a Large-Scale Wind Turbine Blade Using Computational Fluid Dynamics

The determination of the circulation for wind turbine blades is an important problem in engineering. In the present study, we develop a specific approach to evaluate the integral that represents mathematically the circulation. First the potentialities of the method are assessed using a two-dimensional NACA64_A17 airfoil as a testbed and evaluating the influence of different integration paths and angles of attack on the circulation value. Then the method is applied to blades with different relative heights in order to provide useful reference data to be used for the optimization and reverse design of wind turbine blades. As shown by the results, the integral value changes with the integral path, and an "optimal circle radius" exists. We calibrate the integral value by comparing its value with the lift formula. In this was we succeed in showing that there is a certain error when the radius is too small. However, the error can increase rapidly when the radius is too large. When the radius of the circle is 1-6 times the chord length, the error of all integral values is less than 5%. The optimal radius varies with the angle of attack.