Multi-Fidelity Numerical Methods for Aircraft and Wind Turbines: Aerodynamics, Aeroelasticity, and Aeroacoustics

The aerospace and wind energy markets are going through dramatic changes. The first, due to the rise of electric aircraft with multiple rotors in various complex configurations that are incompatible with traditional design methods. The latter, due to the quick growth in wind turbine size and the move to floating offshore installations, which are more complex than their fixed-base onshore counterparts. Hence, there is a clear necessity for fast tools for aerodynamic and aeroelastic design of these new configurations, along with highly accurate methods for late stage verification of aerodynamics and aeroacoustics. The first objective of this thesis is to develop and validate a free wake panel code, exploring its capabilities and applicability to model complex problems relevant to the wind energy and aerospace market. The second objective is to develop methodologies for a high-fidelity lattice-Boltzmann code, also to evaluate the capabilities of such method for problems in wind energy and aerospace that mainstream tools struggle to solve.

The first half of the work focuses on the development and applications of the free wake panel method. After several fundamental verification and validation studies, the method is used to study the nonlinear aerodynamics of an offshore wind turbine undergoing surge, sway, and yaw motions. The method is able to reproduce experimental results and is then used to go beyond the range of motion available in the literature, showing where nonlinear effects start playing a role. The free wake panel method is then used on a highly flexible wing undergoing flutter. The method compares very well with the experimental flutter onset range and is also used on a case with gusts, where corrections to the experiments are proposed. The use of blade and strut pitching on vertical axis wind turbines is investigated next, with a novel combination of pitched elements is proposed, leading to more efficient wake steering. Finally, the free wake panel method is used to investigate propeller-wing interactions on a wing in cruise conditions, showing good agreement with reference cases, and good computational efficiency, due to a mixed fixed/free wake formulation.

The second half of the thesis focuses on high-fidelity lattice-Boltzmann simulations, using the commercial software PowerFLOW(R). The first implementation of a sliding mesh actuator line method is explored, with the advantages and disadvantages quantified. This actuator line method is used, along with blade-resolved simulations, to investigate rotor tip vortex instabilities. Then, the method is validated on a propeller-wing interaction case in cruise and high-lift conditions, with good agreement with experimental data and a deeper flow analysis of slipstream deformation and tip vortex instabilities than what was possible in the experiments. Next, trailing-edge noise of a full wind turbine with serrations is performed and compared to field test data, with good agreement and run times that are compatible with industrial expectations. Finally, a detailed study of leading-edge noise, with a focus on turbulence distortion is performed, where the effects of airfoil thickness on turbulence and noise are investigated in detail.

The conclusion of this work is that free wake panel methods can contribute to wind turbine and aircraft design, but there are cases where lifting line methods for wind turbines and vortex lattice methods for aircraft are sufficiently accurate while being faster. For wake steering studies, the panel method was shown to be useful for finding new solutions, but simulation of wind farms require more stable wakes, such as those obtained with actuator line or vortex particle methods. The scale-resolving lattice Boltzmann method was shown to be very accurate for applications in wind turbine wake dynamics, propeller-wing interaction, trailing and leading-edge noise, making such tool effective for design, able to reduce the amount of experimental campaigns. Several physical insights from the simulations are given throughout the work.