MULTIDISCIPLINARY DESIGN ANALYSIS AND OPTIMIZATION OF INNOVATIVE PROPULSION SYSTEMS AND AIRFRAME INTEGRATION FOR A LOW ENVIRONMENTAL IMPACT

The PhD activity is based on the investigation of new green aeronautical innovations, able to make a positive contribute to the global attempt to reduce human impact on the environment. The research activity was conducted in a three-year time schedule: first and last year were spent at Politecnico di Torino (Italy), while the second year I was host at Virginia Tech (VA, USA) as visiting scholar. The first part of the proposed study mainly focuses on the analysis and optimization of a high-speed turbine disks cavity, and those studies were carried on at the Great Lab, a joint laboratory between Politecnico di Torino and Avio S.p.A. A Multidisciplinary Design Analysis and Optimization approach was selected in order to align this part of the research with the most advanced approaches. An optimization framework was realized by linking together different national research centers, in order to comply with that engineering management philosophy commonly known as Concurrent Engineering. An automatic optimization tool was designed to optimize low-pressure turbine disks performance, by considering new high-speed configurations. Deterministic and stochastic optimizations were performed with the aim of better understanding the considered design space, as well as mostly adopted optimization algorithms were investigated. A code-based deterministic multi-objective optimization approach was finally chosen and its performance was compared to a surrogate-based approach, with the aim of identifying the best optimization methodology and a possible reduction of calculation times. Then trade-offs of radical engine architectures were pursued with the aim of investigating the current scenario of mostly studied Green Engines concepts. The Geared Open Rotor (GOR) engine was chosen in that well-populated scenario, as it presents the highest capability to meet environmental challenges for a short-range aircraft. Geared Open Rotor performance were investigated by modeling its engine cycle. The developed optimization tool was adopted and customized to optimize the disks cavity of the GOR high-speed power turbine, by extending the set of design variables also to the Abstract V required bleed and sealing flows. Finally the specific fuel consumption of the GOR was evaluated by considering the impact of the optimized Power Turbine disks cavity. The second part of this work concerns the study of an innovative concept for nextgeneration Green Aircrafts. The study was conducted at Virginia Tech and at the National Institute of Aerospace (NIA) in a one-year timeframe. The research team was led by three Virginia Tech professors (Dr. Schetz, Dr. Kapania and Dr. Roy). The conducted activity was considered as part of a more wide research project, the Truss Braced Wing. The investigation started from one interesting arrangement for fuselage drag reduction involving a Boundary Layer Ingestion device and engines embedded within the fuselage, proposed and studied by Goldschmied and co-workers starting in the 1950’s. That device was claimed to be potentially able to cancel the parasite drag contribution of a fuselage, therefore NASA started considering its possible application for next-generation Green Aircrafts. Based on existing experimental data provided by Goldschmied papers, the research aim was to understand if it was possible to take advantage of the great potential of such a device. Exhaustive analyses were conducted by using modern RANS-based Computation Fluid Dynamics. Computational grids studies were performed to capture the aerodynamics involving both the external shape and the internal ducts, interested by a very complex flow. Several reference fuselage-like prolate spheroids were investigated and detailed analyses of the required power of the embedded engine were pursued. Finally, sensitivity analysis of the results due to different computational grids refinements and turbulence models were conducted, as well as iterative convergence errors were carefully investigated. Hence, an accurate assessment of the potential for the boundary layer control and static pressure thrust generation with an embedded propulsor concept was conducted.