Continued Validation of the AeroDyn Subroutines Using NREL Unsteady Aerodynamics Experiment Data

Full-scale wind tunnel tests of the NREL Unsteady Aerodynamics Experiment (UAE) Phase VI permitted unprecedented control and measurement of inflow to the UAE rotor. This in turn has allowed in-depth validation of the AeroDyn wind turbine aerodynamics software. This validation began with comparison of simple cases (i.e., fixed yaw, fixed pitch, no teeter), with results presented last year [2]. Among the findings of that study was the significant increase in section lift along the rotor blades due to the 3–dimensional flow over the UAE rotor. This delayed stall was not adequately accounted for in the AeroDyn model. This continued validation effort looks into delayed stall and the static and dynamic behavior of the Generalized Dynamic Wake (GDW) model in AeroDyn. Validation is accomplished through comparison of UAE data and simulation results for the following cases: • Uniform inflow (upwind, zero yaw error), • Step pitch changes on an operating rotor, • A teetering rotor at various yaw angles, and • Downwind rotor released into flee yaw from various initial yaw error positions. Results presented allow us to draw several conclusions. The Du and Selig delayed stall correction adequately models the increase in C_L, but the suggested decrease in C_D of that model does not agree with observations in the data. The time lag coefficient in the GDW model agrees well with observations in the rapid pitch change UAE data. The phase of teeter response for the GDW model agrees better with data than for the equilibrium wake model. Dynamic stall provides significant additional damping to the teeter motion. The choice of wake model also greatly affects the yaw rate in the yaw release simulations.