An Experimental Investigation of Scale Effects on Offshore Wind Turbine Blades

In hydrodynamic model testing, the choice of the scaling factor is often a compromise between the size of the facility and close matching of the characteristic numbers such as Reynolds and Froude. When combining the two aspects into model testing of offshore floating wind turbines, limitations on the size of the model test facilities apply and it is not possible to use both Froude and Reynolds number scaling effects at the same time. To investigate Reynolds number similarity, two wing geometries, a NACA 0012 and a NREL S825 were manufactured in several sizes and tested at identical Reynolds numbers. The wakes behind the airfoils were measured using Particle Image Velocimetry. One would expect to obtain similar results, but differences in the wake profiles were observed. Understanding the mechanisms involved are important as it then enables model building techniques to be improved, and thus make model testing more effective.