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 wel

A Multi-Objective Design Optimization Approach for the Preliminary Design of High Speed Low Pressure Turbine Disks for Green Engine Architectures

The so-called Green Engine architectures are deeply investigated by the scientific community with the aim of reducing fuel consumption and noise emissions by 50%, and pollutants by 80%, environmental targets established by the Advisory Council for Aeronautical Research in Europe to be achieved by 2020. Low pressure turbine improvements will be important to increase the efficiency of the two most innovative propulsive architectures, the Geared Turbofan and the Open Rotor Engine. The low pressure turbine is released from the fan and can rotate at higher speed values, implying a reduction in fuel consumption. Due to a higher rotational speed, low pressure turbine disks design needs careful considerations due to their higher stress level and reduced burst limit. This paper presents a multi-objective hybrid optimization methodology designed to study high speed low pressure turbine disks. The presented study falls within the preliminary design phase, thus a code based on finite differences was used to perform an optimization study of high speed low pressure turbine disks. The objective functions of the constrained multi-objective optimization were the minimization of the disks weight and the maximization of the burst speed, and a hybrid approach was pursued to better investigate the design space and find the optimum. Then a surrogate-model-based hybrid optimization was conducted to reduce computational time while ensuring the analysis accuracy. A trade-off of most common approximation strategies was conducted. Distributed computing was used involving three national research centers, and parallel computing was adopted to spread the calculation tasks on local workstations. Numeric and Finite-Element-Methodology-based validations followed. This study provides an innovative approach to design such critical components by reducing disks weight by 15% and computational time by 30% if compared to traditional design methodologies. Furthermore, a good match between optimal solutions was found, thus justifying a surrogate-model-based-approach that led to further gains in computational time

IMPACT OF AN OPTIMIZED POWER TURBINE DISKS CAVITY ON GEARED OPEN ROTOR PERFORMANCE - A MULTIDISCIPLINARY APPROACH IN THE PRELIMINARY DESIGN

A constantly growing number of studies have been oriented to Green Aircraft and Green Engine concepts during last years in order to reduce pollutants and carbon-dioxide production by 2020. Ultra high by-pass engines are recently getting the highest interest by academia, research centers and industries. Among the most recent research activities, many studies are focused on geared architectures, the Geared Turbofan (GTF) and the Geared Open Rotor (GOR). The GOR architecture seems to be the most promising radical architecture for short-range aircraft as climbing and landing phases interest the major part of the whole mission. Our work takes place in the most recent research activities regarding a GOR-like engine, and can fit its preliminary design phase. A multidisciplinary modular simulation environment was developed to let researchers the chance to directly relate the considered disciplines. Introductory trade-off studies were carried on to effectively show GOR capabilities amongst the most innovative engines. A reference military core engine was used for the considered GOR engine, as previously done by General Electric for its original open rotor engine. GOR performance were predicted on-design and off-design, by relating to corporate inputs. Optimization studies of the GOR high-speed power turbine disks cavity were performed to reduce disks weight and cooling flows, complying with several engineering constraints provided by the industry. Finally the optimization outcomes were linked to the performance code to capture their impact on the overall engine efficiency and specific fuel consumption. Results show that it is possible to get an improvement in the specific fuel consumption by minimizing the required cooling flows of the GOR power turbine. Moreover, for a required thrust level, engine weight may be reduced