Design and Testing of Scale Model Wind Turbines for Use in Wind/Wave Basin Model Tests of Floating Offshore Wind Turbines

Abstract

Model basin testing is a standard practice in the design process for offshore floating structures and has recently been applied to floating offshore wind turbines. 1/50th scale model tests performed by the DeepCwind Consortium at Maritime Research Institute Netherlands (MARIN) in 2011 on various platform types were able to capture the global dynamic behavior of commercial scale model floating wind turbine systems; however, due to the severe mismatch in Reynolds number between full scale and model scale, the strictly Froude-scaled, geometrically similar wind turbine underperformed greatly. This required significant modification of test wind speeds to match key wind turbine aerodynamic loads, such as thrust. To execute more representative floating wind turbine model tests, it is desirable to have a model wind turbine that more closely matches the performance of the full scale design. This work compares the wind tunnel performance, under Reynolds numbers corresponding to model test Froude-scale conditions, of an alternative wind turbine designed to emulate the performance of the National Renewable Energy Laboratory (NREL) 5 MW turbine. Along with the test data, the design methodology for creating this wind turbine is presented including the blade element momentum theory design of the performance-matched turbine using the open-source tools WT_Perf and XFoil. In addition, a strictly Froude-scale NREL 5 MW wind turbine design is also tested to provide a basis of comparison for the improved designs. While the improved, performance-matched turbine was designed to more closely match the NREL 5 MW design in performance under low model test Reynolds numbers, it did not maintain geometric similitude in the blade chord and thickness orientations. Other key Froude scaling parameters, such as blade lengths and rotor operational speed, were maintained for the improved designs. The results of this work support the development of protocols for properly designing scale model wind turbines that emulate the full scale design for Froude-scale wind/wave basin tests of floating offshore wind turbines.