Analysis the vortex ring state and propeller state of floating offshore wind turbines and verification of their prediction criteria by comparing with a CFD model

In our previous study, the vortex ring state (VRS) prediction criteria were introduced from helicopter's realm and applied to floating offshore wind turbines (FOWTs). The existence of the VRS on FOWTs was also successfully predicted. However, the prediction criteria we used have not been verified by comparing them with similar studies because of the lack of reference publications — until recently. In this paper, a comparative analysis of the VRS phenomenon of an FOWT is done and aerodynamic performance of the FOWT is evaluated. We compare the VRS results predicted based on the criteria we proposed with a new study about the VRS by means of a computational fluid dynamics (CFD) method. The aerodynamic performance of an FOWT undergoing surge motions is simulated with an in-house code based on a free wake vortex method. Similarities and differences of the two studies are compared and discussed. The propeller state of the rotor is further analyzed to gain a deeper understanding of the working state change of FOWTs as well as to strengthen the research in this area.