Aerodynamic Design of the NASA Rotor 67 for Non Uniform Inflow Due to Boundary Layer Ingestion
As the demand to improve the fuel efficiency of current commercial aircraft increases, new commercial airliner concepts such as the Blended Wing Body has been researched on and studied in various aspects over the years as an efficient alternative to the conventional transport configuration. One particular aspect of the Blended Wing Body is the use of the propulsive fuselage concept. In this concept, the fuselage boundary layer is ingested by the engine and this is aimed at producing benefits such as improved fuel efficiency, reduced ram drag as well as lower structural weight of the engine. During the ingestion process, the low momentum boundary layer is re-energized by the propulsion system before exiting into the atmosphere. In this way, the ingested flow does not contribute to the wake deficit and hence, the overall drag of the aircraft is reduced. Since thrust equal drag in steady and level flight, and power is equal to thrust multiplied by velocity, the reduction in drag implies a reduction in the power required to drive the vehicle.In essence, the ingestion of the boundary layer which leads to a lower inlet stagnation pressure represents a direct thermodynamic penalty. However, the momentum deficit captured by the engine represents a drag reduction to the aircraft. In this way, the propulsion system performance suffers a decrease in engine efficiency while the aircraft drag is reduced in proportion to the amount of boundary layer flow that is ingested. Therefore, a trade-off exists between the increase in aircraft drag reduction and the decrease in engine performance as more boundary layer is consumed. Another important concern is the significant flow distortion which can lead to increased vibration and fatigue of the fan and compressor blades in particular. This flow distortion is characterized by the distortion coefficient, a standard widely used in the aircraft engine industry. While it was found that the ingestion of the boundary layer can provide a decrease in fuel burn of several percentages, the benefits of boundary layer ingestion have shown to be very sensitive to the magnitude of the fan and duct losses. Hence, it is crucial that fan designers are able to design new rotor blades that are able to withstand the flow distortion while ensuring that engine performance degradation is kept to a minimum in order to maximize the overall gain in fuel efficiency.The main aim of this research is therefore to understand and analyse the rotor performance under both uniform and non-uniform inflow condition. This will then provide insights into the main fluid mechanism affecting rotor performance under such conditions. As such, the early phase of this research was focused on the development of an in-house blade modeller which was then later used in the parametrization and reconstruction of the NASA Rotor 67. Other than the development of the Blade Modeller, this research was also focused on the coupling of an open-source meshing software, SALOME to the Blade modeller which will then allow the user to achieve automated meshing needed for the design optimization process. The main highlight of this thesis is on the detailed analysis of the blade to blade domain as well as the overall rotor performance under non uniform inflow condition.
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