Detailed Experimental Investigation of the Aerodynamics and Blade/Tower Interaction of a 1.5 MW Wind Turbine in a Downwind Configuration

We present a detailed experimental investigation of the flow details of the blade/tower interaction on a 1.5 MW wind turbine operated in a downwind configuration. The study aims to address claims of shortcomings in the downwind turbine concept, such as impulsive blade loading and the generation of low-frequency noise. The measurement campaign was part of a comprehensive project conducted by the National Renewable Energy Laboratory and its partners exploring the feasibility, reliability, and performance of wind turbines whose rotors are oriented downwind instead of the more traditional upwind configuration. The campaign measured blade pressure distributions at two radial positions on one blade and pressure on the tower surface at the position corresponding to the blade path of the outboard instrumented section on the blade. Pressure distributions on the blade and tower were measured using add-on pressure belts, and local inflow was measured on the blade with two five-hole probes. Despite challenging weather conditions, two measurement campaigns of different durations were successfully completed. The analysis of the datasets indicates the data are of good quality and highlights the importance of dynamically reconstructing the tower pressure measurements that used pressure belts up to 10.7 m in length. Impulse loading is found to be 100-150 N m-1 on the tower and 200-500 N m-1 on the blade over a time span of approximately 0.3 s. The detailed pressure measurements make the dataset well suited for use in validating high-fidelity models such as full three-dimensional computational fluid dynamics rotor simulations that include tower flow.