Pier Francesco Melani

This paper presents an open-access dataset that has been developed to provide high-fidelity aerodynamic polars for a wide range of wind turbine airfoils, computed using a consistent computational fluid dynamics (CFD) methodology. The database includes lift, drag, and moment coefficients across multiple Reynolds and Mach numbers. Coefficients are computed with both fully turbulent and free transition boundary layers between positive and negative stall angles. A blend of the free transition and fully turbulent coefficients is also included. Beyond the stall region, state-of-the-art post-stall extrapolation models are used, the calibration parameters of which are derived from a number of high-fidelity calculations at various angles of attack in separated flow. The data are relevant for wind turbine design, modeling, and simulation and reflect representative airfoil performance along the span of modern, large-size offshore rotors. The database includes FFA-W3, FFA-W2, FFA-W1, DU, FX-77, and the recently developed OSO families of airfoils. All simulations are performed using validated numerical methods and span a range of conditions typical of utility-scale offshore turbines. The paper discusses the dataset and its key differences from other open-access data, as well as some general trends that can be noted in the aerodynamic coefficients; such a discussion is made possible by the volume of data produced and is specifically tailored to wind turbine applications.

Despite an increasing number of experimental and numerical studies, the influence of platform motion on wake dynamics (wake recovery and turbulence production) in floating offshore wind turbines is still an open research question. In particular, efforts are being made to understand the accuracy of numerical models in use so far for fixed-bottom turbines when they are applied to floating configurations. Similarly to what has been done in the IEA OC6 task, in this work, a multi-fidelity approach is leveraged to investigate the capabilities of engineering models to capture the wake dynamics of a wind turbine model under imposed motion. In contrast to previous studies, however, many more different operating conditions have been investigated, including surge, pitch, yaw, and wind–wave misalignment cases; moreover, numerical methods are here consistently applied to the same test cases, which are part of the first experimental round of the NETTUNO project. More specifically, free vortex wake (FVW), actuator line model (ALM), and blade-resolved computational fluid dynamics (CFD) simulations have been benchmarked, and their capabilities in predicting the mean wake response and the onset of velocity oscillations in the wake of a floating wind turbine were evaluated. Results showed that FVW methods, if properly tuned, can correctly capture the wake response up to 3 D from the rotor, but to simulate the wake response up to 5 D, higher-fidelity methods are required. Significant improvements are achieved with ALM CFD simulations, even though a URANS approach might struggle to correctly predict the wake dissipation due to the interaction between the free-stream turbulence and wake.

The efficiency gains observed in a pair of closely spaced Darrieus turbines suggest the deployment of multiple turbines as an appealing solution for wind and, particularly, hydrokinetic applications, where the inflow direction is constant. The present study develops some design guidelines for closely spaced hydrokinetic Darrieus turbines by analyzing the trends of both power augmentation and wake development within arrays of multiple rotors, including not only an even number of rotors, which is the usual case in literature, but also an odd one. The analysis is carried out by means of two-dimensional computational fluid dynamics simulations and includes not only the assessment of instantaneous blade forces but also locally sampled flow fields past each blade that allowed the reconstruction of dynamic polar data, contributing to a more comprehensive understanding of the physical mechanisms at play in such compact setups. The study demonstrates a consistent power augmentation mechanism across different layouts, even in the case of an odd number of rotors. This enhancement originates from flow blockage in the mutual interaction areas, favorably altering the inflow angle and subsequently increasing the angle of attack and lift generation. While this mechanism aligns with previous observations on arrays of counter-rotating pairs, its application to multiple turbines introduces complexities due to potential asymmetries in inflow, leading to an uneven power enhancement across turbines within the array. The identified efficiency improvement pattern suggests that maximizing leeward mutual interactions within an array of multiple Darrieus turbines would enhance the overall efficiency of the setup.

The authors proposed a simplified model for the real-time prediction of propellers' thrust in oblique flow, which has shown good accuracy when compared against experimental measurements. The topic and the activity are very interesting, innovative, an...