Aerodynamic analysis for different operating states of floating offshore wind turbine induced by pitching movement

Abstract

The floating offshore wind turbine (FOWT) may experience dynamic stall and complex rotor-wake interaction, such as the vortex ring state (VRS) or propeller working state (PWS), under large platform movements, which can lead to intricate alterations in both aerodynamic parameters and flow states. In this paper, we propose a reliable criterion based on the velocity field of FOWT to distinguish its operating states (VRS or PWS). The aerodynamic characteristics and flow mechanism of the FOWT are considered in details as different operating states induced by a large pitch motion are experienced. Excessive angle of attack (AOA) will cause a dynamic stall, generating a large number of stall vortices and inducing violent fluctuations in the normal and tangential forces of the blade. When the wind turbine experiences VRS or PWS, the continuity of the tip vortex is broken by the blade–vortex or vortex–vortex interaction, complicating the flow state and even resulting in a negative thrust and AOA. In comparison with the remainder of the blade, the blade tip is more likely to experience VRS or PWS owing to its higher movement velocity.