UC Davis

Aerodynamic interactions between spinning rotor blades, rotor wake systems, and the fuselage present formidable challenges to rotorcraft designers. These interactions underpin much of the noise and aerodynamic challenges faced by such vehicles. With the emergence of urban air mobility (UAM) aircraft, especially vehicles with multiple rotors, the complexities and challenges of these interactions have increased dramatically when compared to simpler single-rotor helicopter designs. The need for quieter urban air vehicles requires an in-depth understanding of these interactions. This dissertation seeks to bridge existing knowledge gaps through the application of high-fidelity computational fluid dynamics (CFD) models combined with a high-fidelity model to predict resultant rotorcraft noise. By accurately simulating the aerodynamics and the noise generated by multi-rotor UAM aircraft, this research aims to pave the way for innovative low-noise designs that not only meet technical benchmarks but also fit seamlessly into urban settings by securing the acceptance of city dwellers.A foundational step in this investigation is to ensure the robustness and accuracy of the employed CFD models. To achieve this, the models are meticulously validated against experimental data. A keen emphasis is placed on examining rotor-vortex interactions, especially parallel blade-vortex interactions (BVI). These BVIs are of particular interest because of their propensity to induce rapid aerodynamic changes and significant noise, which can be detrimental to the efficacy and acceptance of UAM vehicles. Progressing from this foundational step, the research delves deeper into a case study involving NASA’s proposed side-by-side rotor vehicle. This study comprehensively evaluates the hovering rotor performance, aerodynamics, and the associated noise generation under varied design scenarios, specifically considering rotor overlaps of 0%, 5%, 15%, and 25%. Furthermore, simulations are performed for scenarios in both free-air and in proximity to the ground, reflecting the varied conditions that urban aerial vehicles might encounter. In out-of-ground situations, higher rotor overlap leads to more intense noise, primarily because of the rotor-to-rotor BVIs. However, for in-ground scenarios, lower or no overlap results in increased noise levels. This rise in noise is attributed to the interaction between the rotor and the upwash flow created by the ground, especially when the rotor is in closer proximity to the ground. This dissertation also undertakes an all-encompassing analysis of the UAM side-by-side rotor aircraft design. This involves not just the rotors, but also the fuselage and wing and its interplay with the aerodynamics and noise. Similar to the ground effect, the upwash flow from the fuselage significantly influences noise generation in scenarios with low or no overlap. The outcomes of this research shed light on the physical mechanisms behind noise generation, the directional patterns of noise propagation, and the intricacies of aerodynamic interactions. In essence, this dissertation offers more than just a deep dive into the technical aspects. It provides invaluable insights, robust models, and guidance for engineers and designers striving to create the next generation of low-noise UAM rotorcraft, ensuring they are both effective, quiet, and amenable to urban integration.