O processo de concepção de uma aeronave é um processo iterativo, e um de seus grandes desafios é o dimensionamento dos motores a serem utilizados, dimensionar seu tamanho, peso e parâmetros de desempenho com os poucos dados de entrada disponíveis. Atualmente os métodos tradicionais valem-se de correlações de dados históricos para estimar os parâmetros geométricos e de desempenho de um motor para uma aeronave em estudos conceituais. Estas estimativas trazem imprecisões, que ficam evidentes durante o processo de concepção, no qual a tração requerida para cumprir a missão da aeronave varia e, consequentemente, o motor deve ser redimensionado. Essa imprecisão causa um grande impacto quando tentamos programar métodos de otimização de projeto automatizados, como otimização de múltiplos objetivos. É necessária uma estimativa robusta para estes métodos gerarem respostas adequadas. O objetivo deste estudo é propor uma metodologia para a geração de dados básicos de motores genéricos a partir de sua tração de referência. O método escolhido foi construir um banco de dados de motores turbofan comerciais, utilizá-lo na geração de relações paramétricas entre informações básicas de entrada durante as fases iniciais de projeto de aeronave - estudos conceituais, quando o motor da aeronave em desenvolvimento ainda não foi escolhido. As relações para o cálculo dos parâmetros de motor são estabelecidas com base em uma análise teórica, evitando reduções de dados históricos com base em relações puramente estatísticas. O dado básico de entrada é a tração necessária para a aeronave na decolagem. Dados de entrada opcionais são: razão de passagem, razão de compressão, altitude de cruzeiro e velocidade de cruzeiro. Os dados de saída do programa são: dimensões geométricas do motor - diâmetro do fan, diâmetro da nacele, comprimento da nacele e peso do motor; dados de desempenho - consumo específico de combustível na decolagem e em cruzeiro, vazão mássica, e tração em cruzeiro; dados de emissões de poluentes, segundo modelos termodinâmicos e relacionados aos dados da ICAO para decolagem - HC e NOx, caso sejam inseridos os dados opcionais. O objetivo proposto foi atingido. A metodologia utilizada gerou um banco de dados de motores turbofan extenso e completo. As correlações propostas demonstraram excelente correlação com os dados do banco de dados, e a ferramenta de cálculo de parâmetros de motor, desenvolvida em Excel, possui uma interface simples e intuitiva, e está apta a auxiliar a engenheiros na execução do dimensionamento de motores e aeronaves durante a fase de estudos conceituais de aeronaves. Os desdobramentos possíveis deste trabalho seriam a geração de banco de dados e correlações para outras classes de motores, como Turboprops ou GTFs, e a utilização das correlações desenvolvidas em desenvolvimentos multi-objetivo.

Propulsion systems like Turboprop engines are generally designed to operate at a narrow range of optimum steady state performance conditions. However, these conditions are likely to vary in an unpredictable manner according to factors such as components aging, structural damages or even the operating environment. Over time, inefficiencies could add up and can lead to expensive fuel consumption or faster component aging. This thesis presents a self-optimizing control scheme, referred as Peak-seeking control, applied to propulsion systems similar to Turboprop engines. Using an extended Kalman filter, the Peak-seeking method is able drive the system to an optimal condition based only on measurements. No prior knowledge of the engine dynamics is required which make the Peak-seeking technique easy to implement and also allow for modularity in the engine design. This study is performed on both a turboprop and a DC motor driving a variable pitch propeller and considers several performance functions to optimize.

Current emphasis on sustained supersonic and hypersonic cruise has sparked interest in more efficient power plants for this flight regime. Cycle studies have shown that the turbofan engine equipped with a supersonic through-flow fan, capable of accepting supersonic axial flow from the inlet, has the potential to be very efficient at the supersonic cruise condition. / Master of Science

Despite many advances in aviation noise control over the past 50 years, the industry is continually striving to reduce noise emissions. Turbofan engine acoustic liners are efficient attenuators of engine noise. Plasma actuators have been used as flow control devices in other settings and will now be studied as an enhancement for acoustic liners. A plasma actuator can excite oscillatory flow or a single direction (bias flow). Both flow types are studied as possible means to excite turbofan liners in order to improve the acoustic performance. Experiments revealed the oscillatory flow as the dominant factor in controlling resonator performance. The phase control of the actuator signal is an important parameter when dealing with the oscillatory flow. The actuator is first applied to a single resonator and then a set of six resonators. The experiments show that with the correct phase, the actuators improved the performance of a single resonator by 3 dB to 5 dB. The results for the array of actuators/resonators mirror the results of a single device. Beyond the improvements in performance, a number of other factors affect the usefulness of the plasma actuator technology in a turbofan environment. The ability of the actuator to produce plasma is susceptible to small imperfections in the device, and this property will likely be amplified in a perforated sheet with embedded actuators. Additional weight and energy consumed by the actuators is another factor to consider. Finally, plasma actuator operation produces ozone, so environmental effects deserve consideration as well. / Master of Science

To mitigate climate change, all sectors must contribute their part. Electric propulsion system is a promising approach to reduce emissions from the aviation industry. A major challenge is however the low energy density in today’s battery technology. Even with today’s leading li-ion batteries, the specific energy density in jet fuel is 48 times larger. Because of the low energy density in any battery technology today, hybrid electric propulsion system could be a bridge between conventional and fully electric propulsion systems. The purpose of this degree project is to explore different designs of a parallel hybrid electric mixed turbofan to minimize the impact aircraft have on the environment. The engine has been designed in Modelon Impact and MATLAB has been used to evaluate the thrust requirement and, the performance and weight calculation of the electrical power system. Furthermore, the conventional engine was validated against GasTurb. Three different designs were evaluated, i.e., design #1 (reference engine with hybridization), #2 (decreased OPR) and #3 (increased BPR and decreased FPR) with two different weights of the electrical power system. None of the designs showed a reduction in terms of the total fuel consumption during the whole mission profile. However, design #3 showed the most beneficial results in terms of reducing the specific fuel consumption and could reduce the fuel consumption in the climb segment the most among the three different designs.

Inlet distortion is an important consideration in fan performance. Distortion can be caused through flight conditions and airframe-engine interfaces. The focus of this paper is a series of high-fidelity time accurate Computational Fluid Dynamics (CFD) simulations of a multistage fan. These investigate distortion transfer and generation as well as the underlying flow physics of these phenomena under different operating conditions. The simulations are performed on the full annulus of a 3 stage fan. The code used to carry out these simulations is a modified version of OVERFLOW 2.2 developed as part of the Computational Research and Engineering Acquisition Tools and Environment (CREATE) program. Several modifications made to the code are described within this thesis. The inlet boundary condition is specified as a 1/rev total pressure distortion. Simulations at choke, design, and near stall points are analyzed and compared to experimental data. Analysis includes the phase and amplitude of total temperature and pressure distortion through each stage of the fan and blade loading plots. An understanding of the flow physics associated with distorted flows will help designers account for unsteady flow physics at design and off-design operating conditions and build more robust fans with a greater stability margin.

Aircraft engines are one of the most heavily instrumented parts of an aircraft, and the data from various types of instrumentation across these engines are continuously monitored both offline and online for potential anomalies. Vibration monitoring in aircraft engines is traditionally performed using an order tracking methodology. Currently, there are no representative and efficient physics-based models with the adequate fidelity to perform vibration predictions in aircraft engines, given various parametric dependencies existing among different attributes such as temperature, pressure, and external conditions. This gap in research is primarily attributed to the limited understanding of mutual interactions of different variables and the nonlinear nature of engine vibrations. The objective of the current study is three-fold: (i) to present a preliminary investigation of tracked order vibrations in aircraft engines and statistically analyze them in the context of their operating environment, (ii) to develop data-driven modeling methodology to approximate a dynamical system from input-output data, and (iii) to leverage these data-driven modeling methodologies to develop highly accurate models for tracked order vibration in a turbo-fan engine valid over a wide range of operating conditions. Off-the-shelf data-driven modeling techniques, such as machine learning methods (eg., regression, neural networks), have several drawbacks including lack of interpretability and limited scope, when applying them to a complex multiscale multi-physical dynamical system. Moreover, for dynamical systems with external forcing, the identified model should not only be suitable for a specific forcing function, but should also generally approximate the input-output behavior of the data source. The author proposes a novel methodology known as Wavelet-based Dynamic Mode Decomposition (WDMD). The methodology entails using wavelets in conjunction with input-output dynamic mode decomposition (ioDMD). Similar to time-delay embedded DMD (Delay-DMD), WDMD builds on the ioDMD framework without the restrictive assumption of full state measurements. The author demonstrates the present methodology's applicability by modeling the input-output response of an Euler-Bernoulli finite element beam model, followed by an experimental investigation. As a first step towards modeling the tracked order vibration amplitudes of turbofan engines, the interdependencies and cross-correlation structure between various thermo-mechanical variables and tracked order vibration are analyzed. The order amplitudes are further contextualized in terms of their operating regime, and exploratory data analyses are performed to quantify the variability within each operating condition (OC). The understanding of complex correlation structures is leveraged and subsequently utilized to model tracked order vibrations. Switching linear dynamical system (SLDS) models are developed using individual data-driven models constructed using WDMD, and its performance in approximating the dynamics of the $1^{st}$ order amplitudes are compared with the state-of-the-art time-delay embedded dynamic mode decomposition (Delay-DMD) and Lasso regression. A parametric approach is proposed to improve the model further by leveraging previously developed WDMD and Delay-DMD methods and a parametric interpolation scheme. In particular, a recently developed pole-residue interpolation scheme is adopted to interpolate between several linear, data-driven reduced-order models (ROMs), constructed using WDMD and Delay-DMD surrogates, at known parameter samples. The parametric modeling approach is demonstrated by modeling the transverse vibration of an axially loaded finite element (FE) beam, where the axial loading is the parameter. Finally, a parametric modeling strategy for tracked order amplitudes is presented by constructing locally valid ROMs at different parametric samples corresponding to each pass-off test. The performance of the parametric-ROM is quantified and compared with the previous frameworks. This work was supported by the Rolls-Royce Fellowship, sponsored by the College of Engineering, Virginia Tech. / Doctor of Philosophy / Vibrations in commercial aircraft engines are of utmost importance as they directly translate to aviation health and safety, and hence are continuously monitored both online and offline for potential abnormalities. Notably, this is of increased interest with the abundance of air transportation in today's world. However, there is limited understanding of the complex higher vibration in aircraft engines. Vibration engineers often face ambiguity when interpreting higher vibrations. This can often lead to a lengthy investigative process resulting in longer downtime and increased testbed occupancy, ultimately leading to revenue loss. It is often hypothesized that prior engine running conditions such as shutdown/cooling time between one engine run to another engine run affect the vibration profile. Nonetheless, there exists a gap in understanding tying together various historical operational conditions, temperature, pressures, and current operational conditions with the expected vibration in the engine. This study aims to fill some of these gaps in our understanding by proposing a data-driven strategy to model the vibrations in commercial aircraft engines. Subsequently, this data-driven model can serve as a baseline model to compare the observed vibrations with the model predicted vibration and supplement physics-based models. The data for the present study is generated by operating a commercial turbofan engine in a testbed. With the advent of machine learning and data fusion, various data-driven techniques exist to model dynamical systems. However, the complexity of the turbofan engine vibrations calls for developing new techniques applicable towards modeling the vibration characteristics of a turbofan engine. Specifically, this dissertation details the development of a novel methodology called Wavelet-based Dynamic Mode Decomposition (WDMD) and applies the technique to model input-output characteristics of various dynamical systems ranging from a numerical finite element (FE) beam to an experimental free-free beam to shaft vibrations in a turbofan engine. The study finally presents an improved modeling framework by incorporating the existing techniques with parametric dependencies. This enables the existing method to consider slight differences existing from one engine run to another, such as the history of the engine, the shutdown time, and the outside environmental parameters.

Next generation aircraft design focuses on highly integrated airframe/engine architectures that exploit advantages in system level efficiency and performance. One such design concept incorporates boundary layer ingestion which locates the turbofan engine inlet near enough to the lifting surface of the aircraft skin that the boundary layer is ingested and reenergized. This process reduces overall aircraft drag and associated required thrust, resulting in fuel savings and decreased emissions; however, boundary layer ingestion also creates unique challenges for the turbofan engines operating in less than optimal inlet flow conditions. The engine inlet flow profiles predicted from boundary layer ingesting aircraft architectures contain complex distortions that affect the engine operability, durability, efficiency, and performance. One component of these complex distortion profiles is off-axial secondary flow, commonly referred to as swirl. As a means to investigate the interactions of swirl distortion with turbofan engines, an experiment was designed to measure distorted flow profiles in an operating turbofan research engine. Three-dimensional flow properties were measured at discrete planes immediately upstream and immediately downstream of the fan rotor, isolating the component for analysis. Constant speed tests were conducted under clean and distorted test conditions. For clean tests, a straight cylindrical inlet duct was attached to the fan case; for distorted tests, a StreamVane swirl distortion generator was inserted into the inlet duct. The StreamVane was designed to induce a swirl distortion matching results of computation fluid dynamics models of a conceptual blended wing body aircraft at a plane upstream of the fan. The swirl distortion was then free to develop naturally within the inlet duct before being ingested by the engine. Results from the investigation revealed that the generated swirl profile developed, mixed, and dissipated in the inlet duct upstream of the fan. Measurements immediately upstream of the fan rotor leading edge revealed 50% reduction in measured flow angle magnitudes along with evidence of fanwise vortex convection when compared to the StreamVane design profile. The upstream measurements also indicated large amounts of secondary flow entered the fan rotor. Measurements immediately downstream of the fan rotor trailing edge demonstrated that the fan processed the distortion and further reduced the intensity of the swirl; however, non-uniform secondary flow persisted at this plane. The downstream measurements confirmed that off-design conditions entered the fan exit guide vanes, likely contributing to cascading performance deficiencies in downstream components and reducing the performance of the propulsor system. / Master of Science

Boundary Layer Ingestion (BLI) is currently being researched as a potential method to improve efficiency and decrease emissions for the next generation of commercial aircraft.  While re-energizing the boundary layer formed over the fuselage of an aircraft has many system level benefits, ingesting the low velocity boundary layer flow through a serpentine inlet into a turbofan engine adversely affects the performance of the engine.  The available literature has only yielded studies of the effects of this specific type of inlet distortion on engine performance in the form of numerical simulations.  This work seeks to provide an experimental analysis of the effects of BLI-type distortion on a turbofan engine's performance.  A modified JT15D-1 turbofan engine was investigated in this study.  Inlet flow distortion was created by a layered wire mesh distortion screen designed to create a total pressure distortion profile at the aerodynamic interface plane (AIP) similar to NASA's Inlet A boundary layer ingesting inlet flow profile.  Results of this investigation showed a 15.5% decrease in stream thrust and a 14% increase in TSFC in the presence of BLI-type distortion. Flow measurements at the AIP and the bypass nozzle exit plane provided information about the losses throughout the fan flow path.  The presence of the distortion screen resulted in a 24% increase in mass-averaged entropy production along the entire fan flow path compared to the non-distorted test.  A mass-averaged fan flow path efficiency was also calculated assuming an isentropic process as ideal.  The non-distorted fan flow path efficiency was computed to be 60%, while the distorted fan flow path efficiency was computed to be 50.5%, a reduction in efficiency of 9.5%.  The entropy generation between ambient conditions and the AIP was compared to the entropy production along the entire fan flow path.  It was found that the majority of entropy generation occurred between the AIP and bypass nozzle exit.  Based on flow measurements at the bypass nozzle exit plane, it was concluded that inlet flow distortion should be located away from the tip region of the fan in order to minimize losses in a very lossy region.  It was also determined that the fan and bypass duct process the different regions of the total pressure distortion in different ways.  In some regions the entropy production decreased for the distorted test compared to the clean test, while in other regions the entropy production increased for the distorted test compared to the clean test.  Finally, it was found that small improvements in total pressure and total temperature variation at the bypass nozzle exit plane will greatly improve the fan flow path efficiency and entropy generation, thereby decreasing performance losses. / Master of Science

The combination of traditional passive acoustic liners with Herschel-Quincke (HQ) waveguides is proposed in this work as a device for Turbofan Engine Noise Control. The approach consists of installing circumferential arrays of HQ tubes on the lined sector of the inlet of a turbofan engine. A theoretical model is developed to predict the performance of this system assuming that the engine inlet is a circular lined duct with uniform mean flow. The tube-duct interfaces are modeled as finite piston sources that couple the sound field inside the duct with the dynamics of the HQ tubes. The finite piston source radiation is modeled in terms of a new closed form Green's function, which is found as the solution of the non-homogeneous convected acoustic wave equation with soft wall boundary conditions. The Green's function is extended from a point source to a finite piston by using the Divergence Theorem in the appropriate form. The dynamics of the HQ tube are both modeled as plane waves inside a straight tube and experimentally determined. The experimental determination of the HQ-dynamics is undertaken using impedance tubes with a 4-microphone technique. The newly developed theoretical model was used to predict the performance of a combined HQ-Liner system, which was tested on a scale simulated turbofan rig. The model is validated for broadband noise with the experimental data obtained from this test rig. The analytical predictions are shown to correlate well with experimental data. The results of the application of a HQ-Liner on a turbofan engine show a great potential in order to improve the performance of traditional passive acoustic liners. / Ph. D.