This work concerns high-fidelity numerical simulations of a rotor wake, with focus on the tip vortices and their stability. Blade-resolved and actuator line lattice-Boltzmann simulations are performed on a symmetric baseline rotor, as well as on a rotor with asymmetries. The asymmetry has the purpose of destabilizing the tip vortices to enhance wake recovery and hence the performance of potential downstream turbines. Limitations in the actuator line method are highlighted, and we show the potential of addressing these limitations with a so-called “preset” actuator line, where the forces are extracted from blade-resolved simulations, or an analytical load model, which as input only requires the thrust and power coefficients. Simulations agree well with experimental results and leapfrogging is captured, even with a coarse actuator line simulation. The asymmetric rotor is shown to improve power in the far-wake by 12%.

Numerical simulations of a wind turbine blade with and without trailing-edge serrations are validated with full-scale field test of a 130 m diameter onshore wind turbine. Simulations focus on trailing-edge noise and are conducted on extruded airfoil sections of the blade using the lattice-Boltzmann method and very large eddy simulations, which are then propagated to the far-field using the Ffowcs Williams-Hawkings approach, simulating the rotation of the sections and the noise of the entire rotor. Far-field noise spectra at two mean wind speeds are used for validation, with the sound power level of the simulations being within 2.5 dB of field test and the total noise reductions attributed to the serrations being captured within 0.6 dB.

Vertical axis wind turbines (VAWTs) have been identified as a technology that, in association with wake steering, can increase power density of wind farms. In this study, we validate a free wake method for VAWT wake prediction, which leads to satisfactory results. We then use this method to simulate wake steering by means of fixed pitched blades and struts. We demonstrate that combining pitched wakes and struts can lead to very advantageous wake behavior, but only when the interactions between the tip vortices are taken into account. The possibility to inject more high momentum flow into the wake while moving the vortex system away from the next turbine could make pitched blades and struts a powerful tool for future wind farms.

With distributed propulsion and electric vertical take-off and landing aircraft on the rise, fast and accurate methods to simulate propeller slipstreams and their interaction with aircraft components are needed. In this work, we compare results obtained with a filament-based free wake panel method to experimental and previously validated numerical data. In particular, we study a propeller-wing configuration at zero angle of attack and the aerodynamics of the blade-resolved slipstream interaction with the wing. We use a prescribed wake on the wing and a free wake on the propeller, which greatly accelerate the computations. Results indicate that, while forces are overpredicted due to the inviscid nature of the panel method, the free wake is able to capture the slipstream deformation and shearing with remarkable success. We find that a filament-based free wake panel method can be a useful tool for propeller-wing interaction in preliminary aircraft design.

Simulating entire wind farms with an actuator line model requires significant computational effort, especially if one is interested in wake dynamics and wants to resolve the tip vortices. A need to explore unconventional approaches for this kind of simulation emerges. In this work, the actuator line method is implemented within a lattice-Boltzmann flow solver, combined with a sliding mesh approach. Lattice-Boltzmann solvers have advantages in terms of performance and low dissipation, while the sliding mesh allows for local refinement of the blade and tip vortices. This methodology is validated on a well-documented case, the NREL Phase VI rotor, and the local refinement is demonstrated on the NREL 5 MW rotor. Results show good agreement with reference Navier–Stokes simulations. Advantages and limitations of the sliding mesh approach are identified.

This paper presents low speed fluid structure interaction simulations of a highly flexible wing at various flow conditions, including flutter and excitation from sinusoidal gusts. Such wings are becoming more relevant in recent years, due to their potential for improving aerodynamics and reducing weight, while their flutter characteristics are particularly challenging to address, as the modal properties of the wings change as deflections increase. Calculations are based on time domain coupling of a geometrically exact beam structural model and a 3D free wake panel method, modeling the outer surface of the wing, which allow for nonlinear effects in terms of geometrical deformations and the flow at low computational cost. Static and aeroelastic wing deflections are in line with experimental data of the Pazy wing, which is a benchmark for highly flexible wings from Technion. Two flutter mechanisms are predicted within 1 to 3 m/s of the experimental range. An analysis of the flutter modes is performed, showing that the second torsion mode plays a role in flutter, something that had not been published before. Limit cycle oscillations are achieved and are shown to compare well with reference data, with the frequency being within 1% of the experimental value. Finally, results of gust simulations of the Pazy wing are compared to data from experiments and corrections for the wind tunnel measurements are proposed, which should facilitate future validation efforts. This work serves as a contribution to the Pazy wing dataset and is a step towards mid-fidelity simulations for more complex configurations.

We investigate the aerodynamics of a surging wind turbine with numerical simulations based on a free wake panel method. We start by demonstrating the method's capability to simulate a plunging airfoil, which provides some insights that are later used to interpret results of a surging rotor. We then validate the method on a non-surging wind turbine and discuss the strengths and weaknesses of our approach. Next, we focus on the UNAFLOW case: a surging wind turbine which was modelled experimentally and with various numerical methods. Good agreement with experimental data is observed for amplitude and phase of the thrust with surge motion. For the first time, we achieve numerical results of a wind turbine wake that accurately reproduce experimentally verified effects of surging motion. Finally, we extend our simulations beyond the frequency range of the UNAFLOW experiments and reach results that do not follow a quasi-steady response. Using the plunging airfoil data, we justify the behavior observed in the non-linear range. Our work seeks to contribute a different method to the pool of results for the UNAFLOW case, while extending the analysis to conditions that have not been simulated before.