From test site to flume: replication and quantification of tidal turbine blade fatigue loads in turbulent flows

In this paper experiments were performed on an instrumented 1/20th scale turbine using static grids to generate turbulent flows in a circulating water flume and also at a small-scale tidal test site. Fatigue Damage Equivalent Loads (FDEL’s) were calculated to allow cross comparison between different cases. The results of this research demonstrate that a wide range of turbulent flow conditions can be generated using varying geometry grids, locating the turbine at varying distances downstream. It is possible in the laboratory to closely replicate flow conditions from a real tidal site with corresponding replication of measured fatigue loads. There was a 5-fold increase in fatigue damage acting on the turbine at the tidal test site compared to the typical low turbulence laboratory case. It was also found that the increase in fatigue damage due to increasing turbine rotational speed was only 10% of that due to increasing ambient turbulence thus the ambient flow conditions are critical in determining fatigue loading. This work found that exact replication of turbulent characteristics was not required to match fatigue damage loads between the flume and real site, but a relatively close match was sufficient.