Geometric and kinematic similarity are readily achieved by the application of constant geometric scale factor and the maintenance of the tip speed ratio, respectively. It is highly challenging to match the performance of the scaled rotor for the coefficients such as coefficient of power ( Cp), coefficient of torque ( Cq), and the coefficient of thrust ( Ct), to a full scale reference rotor due to the incompatibility of the three primary scaling criteria, the maintenance of geometric, kinematic, and dynamic similarity between model and full scale. This can be attributed to the complexities involved in accomplishing the three scaling laws, which has to be followed to design a scaled rotor that matches the performance of full scale reference rotor. To predict the global loads in well-ordered experimental conditions by scaling down the wind turbine rotor is challenging. Scaled Rotor for Unsteady Aerodynamic Experiments To gauge the accuracy of engineering numerical codes LR AeroDyn and LR-uBEM, high fidelity CFD model was developed and validated against the experimental simulation. The LR-uBEM model implements the dynamic inflow model based on the elemental aerodynamic loads prediction of individual blades. LR has enhanced the BEM code (LR-uBEM) to simulate the unsteady aerodynamic behavior of the rotors. The BEM-based AeroDyn model was modified (LR AeroDyn) to predict the hydrodynamic load on to the scaled rotor. The experiments are conducted with the focus on surge motion and its effects on aerodynamic performances. A scaled down model of the NREL 5 MW rotor was designed and tested in the wave tank (immersed in the water) to match the Reynolds number Re, as in field operation. The platform motions significantly affect the power and thrust characteristics of the rotor almost to the same order as the effect of tip speed ratio (TSR) and the blade angle. As platform motions of FOWT has greater influence on the unsteady aerodynamic response, a scaled model of the rotor was designed to study the effect. Experiments on scaled rotor provides an insight on the aerodynamic loading of the rotor and to validate the non-linear models. Lloyds Register (LR) has been actively involved in the development of numerical models and experimental modelling. ![]() Almost in all frequencies and amplitudes, CFD, LR-BEM and LR-uBEM predictions of mean thrust shows a good correlation with experimental results. Also, the surging motion significantly influences the windmill operating state due to strong flow interaction between the rotating blades and generated blade-tip vortices. It is shown that the unsteady aerodynamic loads of FOWT are highly sensitive to the changes in frequency and amplitude of the platform motion. The influence of platform surge amplitude together with the tip speed ratio on the unsteady aerodynamic loading has been simulated through unsteady CFD. The current study examines the predictions of numerical codes by comparing with unsteady experimental results of a scaled floating wind turbine rotor. ![]() Accurate prediction of the unsteady aerodynamic loads is imperative for determining the fatigue life, ultimate loads on key components such as FOWT rotor blades, gearbox and power converter. ![]() Aerodynamic performance of a floating offshore wind turbine (FOWT) is significantly influenced by platform surging motions.
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