Multidisciplinary optimisation of aero-engines using genetic algorithms and preliminary design toolsWhellens, Matthew W. January 2003 (has links)
This study investigates a novel methodology for the preliminary design of aeroengines. This involves the modelling of the disciplines that affect the engine's requirements and constraints, their implementation in software format and their coupling into a single unit. Subsequently, this unit is interfaced with an optimiser software. The resulting multidisciplinary optimisation (MDO) tool allows the automation of the traditional, human-based preliminary design process. The investigation of the above-mentioned novel methodology is carried out through the development of a "pilot" MDO tool and its subsequent utilisation in three case studies, characterised by different optimisation scenarios. The selection of each case study is motivated by current research questions, such as aviation's contribution to climate change or the attractiveness of specific novel propulsion concepts. The outcome of the pilot MDO study is considered successful and has been well received by several academic and industrial aero-engine organisations. The choice of the disciplines and of their modelling fidelity allowed a realistic representation of the main disciplinary interactions and tradeoffs that characterise the important phase of preliminary design. The computational effort involved in the solution of the optimisation studies was found to be acceptable, and no major reprogramming was required when different optimisation scenarios were considered. The case studies were investigated with an ease and comprehensiveness that would not have been achievable through a human-based parametric analysis. The positive experience with the pilot MDO tool suggests that an automated methodology for the preliminary design of aero-engines is feasible, applicable and valuable. Its adoption can provide substantial advantages over the traditional human-based approach, such as a reduction in human effort, costs and risk. From this perspective, the pilot study constitutes a first step towards the development of a full-scale MDO tooL usable by aero-engine manufacturers. In the near future, issues like climate change could drive significant modifications in airframe and engine design. A preliminary design MDO tool is therefore timely, and has the potential of making a significant contribution.
No description available.
The increasing demand of more economical and environmentally friendly aero engines leads to the proposal of a new concept – geared turbofan. In this thesis, the characteristics of this kind of engine and relevant considerations of integration on a flying wing aircraft were studied. The studies can be divided into four levels: GTF-11 engine modelling and performance simulation; aircraft performance calculation; nacelle design and aerodynamic performance evaluation; preliminary engine installation. Firstly, a geared concept engine model was constructed using TURBOMATCH software. Based on parametric analysis and SFC target, the main cycle parameters were selected. Then, the maximum take-off thrust was verified and corrected from 195.56kN to 212kN to meet the requirements of take-off field length and second segment climb. Besides, the engine performance at offdesign points was simulated for aircraft performance calculation. Secondly, an aircraft performance model was developed and the performance of FW-11 was calculated on the basis of GTF-11 simulation results. Then, the effect of GTF-11 characteristics performance on aircraft performance was evaluated. A comparison between GTF-11 and conventional turbofan, RB211- 524B4, indicated that the aircraft can achieve a 13.1% improvement in fuel efficiency by using the new concept engine. Thirdly, a nacelle was designed for GTF-11 based on NACA 1-series and empirical methods while the nacelle dimensions of conventional turbofan RB211-525B4 were obtained by measure approach. Then, the installation thrust losses caused by nacelle drags of the two engines were evaluated using ESDU 81024a. The results showed that the nacelle drags account for about 4.08% and 3.09% of net thrust for GTF-11 and RB211-525B4, respectively. Finally, the considerations of engine installation on a flying wing aircraft were discussed and a preliminary disposition of GTF-11 on FW-11 was presented.
Hutcheson, Florence Vanel
17 November 1999
An advanced model of active control of fan noise for ultra high bypass turbofan engines has been developed. This model is based on a boundary integral equation method and simulates the propagation, radiation and control of the noise generated by an engine fan surrounded by a duct of finite length and cylindrical shape, placed in a uniform flow. Control sources, modeled by point monopoles placed along the wall of the engine inlet or outlet duct, inject anti-noise into the duct to destructively interfere with the sound field generated by the fan. The duct inner wall can be lined or rigid. Unlike current methods, reflection from the duct openings is taken into account, as well as the presence of the evanescent modes. Forward, as well as backward (i.e., from the rear of the engine), external radiation is computed. The development of analytical expressions for the sound field resulting from both the fan loading noise and the control sources is presented. Two fan models are described. The first model uses spinning line sources with radially distributed strength to model the loading force that the fan blades exert on the medium. The second model uses radial arrays of spinning point dipoles to simulate the generation of fan modes of specific modal amplitudes. It is shown that these fan models can provide a reasonable approximation of actual engine fan noise in the instance when the modal amplitude of the propagating modes or the loading force distribution on the fan blades, is known. Sample cases of active noise control are performed to demonstrate the feasibility of the model. The results from these tests indicate that this model 1) is conducive to more realistic studies of active control of fan noise on ultra high bypass turbofan engines because it accounts for the presence of evanescent modes and for interference between inlet and outlet radiation, which were shown to have some impact on the performance of the active control system; 2) is very useful because it allows monitoring of any region of the acoustic field; 3) is computationally fast, and therefore suitable to conduct parametric studies. Finally, the potential that active noise control techniques have for reducing fan noise on an ultra high bypass turbofan engine is investigated. Feedforward control algorithms are simulated. Pure active control techniques, as well as hybrid (active/passive) control techniques, are studied. It is demonstrated that active noise control has the potential to reduce substantially, and over a relatively large far field sector, the fan noise radiated by an ultra high bypass turbofan engine. It is also shown that a hybrid control system can achieve significantly better levels of noise reduction than a pure passive or pure active control system, and that its optimum solution is more robust than the one achieved with a pure active control system. The model has shown to realistically predict engine acoustic behavior and is thus likely to be a very useful tool for designing active noise control systems for ultra high bypass turbofan engines. / Ph. D.
06 July 2017
(has links) (PDF)
Fuel consumption and noise reduction trigger the evolution of aircraft engines towards Ultra High Bypass Ratio (UHBR) architectures. Their short air inlet design and the reduction of their interstage length lead to an increased circumferential inhomogeneity of the flow close to the fan. This inhomogeneity, called distortion, may have an impact on the tonal noise radiated from the fan module. Usually, such a noise source is supposed to be dominated by the interaction of fan-blade wakes with Outlet Guide Vanes (OGVs). At transonic tip speeds, the noise generated by the shocks and the steady loading on the blades also appears to be significant. The increased distortion may be responsible for new acoustic sources while interacting with the fan blades and the present work aims at evaluating their contribution. The effects of distortion on the other noise mechanisms are also investigated. The work is based on full-annulus simulations of the Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations. A whole fan module including the inlet duct, the fan and the Inlet and Outlet Guide Vanes (IGVs/OGVs) is studied. The OGV row is typical of current engine architecture with an integrated pylon and two different air inlet ducts are compared in order to isolate the effects of inlet distortion. The first one is axisymmetric and does not produce any distortion while the other one is asymmetric and produces a level of distortion typical of the ones expected in UHBR engines. A description and a quantification of the distortion that is caused by both the potential effect of the OGVs and the inlet asymmetry are proposed. The effects of the distortion on aerodynamics are highlighted with significant modifications of the fanblade wakes, the shocks and the unsteady loading on the blades and on the vanes. Both direct and hybrid acoustic predictions are provided and highlight the contribution of the fan-blade sources to the upstream noise. The downstream noise is still dominated by the OGV sources but it is shown to be significantly impacted by the inlet distortion via the modification of the impinging wakes.
Neale, Tyler P.
2010 May 1900
Laminar flow control has been studied for several decades in an effort to achieve higher efficiencies for aircraft. Successful implementation of laminar flow control technology on transport aircraft could significantly reduce drag and increase operating efficiency and range. However, the crossflow instability present on swept-wing boundary layers has been a chief hurdle in the design of laminar wings. The use of spanwise-periodic discrete roughness elements (DREs) applied near the leading edge of a swept-wing typical of a transport aircraft represents a promising technique able to control crossflow and delay transition to accomplish the goal of increased laminar flow. Recently, the Flight Research Laboratory at Texas A&M University conducted an extensive flight test study using DREs on a swept-wing model at chord Reynolds numbers in the range of eight million. The results of this study indicated DREs were able to double the laminar flow on the model, pushing transition back to 60 percent chord. With the successful demonstration of DRE technology at these lower chord Reynolds numbers, the next logical step is to extend the technology to higher Reynolds numbers in the range of 15 to 20 million typical of smaller transport aircraft. To conduct the flight tests at the higher Reynolds numbers, DREs will be placed on a wing glove attached to the aircraft wing. However, a feasibility study was necessary before initiating the flight-testing. First, a suitable aircraft able to achieve the Reynolds numbers and accommodate a wing glove was identified. Next, a full CFD analysis of the aircraft was performed to determine any adverse effects on the wing flow-field from the aircraft engines. This required an accurate CAD model of the selected aircraft. Proper modeling techniques were needed to represent the effects of the aircraft engine. Once sufficient CFD results were obtained, they were used as guidance for the placement of the glove. The attainable chord Reynolds numbers based on the recommendations for the wing glove placement then determined if the selected aircraft was suitable for the flight-testing.
Metodologia semi-analítica para predição de ruído de banda larga causado pela interação entre a esteira turbulenta do rotor com as aletas da estatora em motores turbofans / Rotor wake turbulence noise semi-analytical methodology in turbofans enginesCarlos Cesar Brochine Junior 29 November 2013 (has links)
A maior parte do ruído de aeronaves é advinda dos motores. Como houve grande avanço no controle do ruído tonal, atualmente grande parte do esforço se dá para redução do ruído de banda larga, que é menos compreendido. O ruído de banda larga é gerado pela interação entre um escoamento turbulento e uma superfície, como por exemplo, a turbulência ingerida interagindo com o rotor, o escoamento na ponta das pás, entre outros. Apesar das diversas fontes citadas, sabe-se que a principal fonte de ruído de banda larga em tal tipo de motor é a interação da esteira turbulenta do rotor com as aletas da estatora. Assim, o presente estudo manterá seu enfoque apenas em tal causa. O objetivo deste então é o desenvolvimento de um modelo capaz de previsão do ruído de banda larga pela interação da esteira turbulenta causada pelo rotor, interagindo com as aletas da estatora, bem como o entendimento da propagação do ruído em duto. A primeira abordagem em relação a tal tipo de ruído é através da previsão do ruído gerado. Para previsão de ruído podem ser utilizados métodos analíticos, numéricos, ou empíricos, cada qual com suas vantagens e penalizações. Para tal, foi utilizado um método semi-analítico, em tais métodos utiliza-se simulação numérica para previsão da característica da turbulência e uma teoria analítica para a geração e propagação do ruído no duto. A principal motivação para o método semi-analítico é sua vantagem em relação aos métodos numéricos que demandam custo computacional extremamente alto e vantagem em relação a métodos analíticos que necessitariam uma demasiada simplificação geométrica. Dessa maneira, utilizou-se a geometria do ANCF, uma plataforma de ensaios desenvolvida pela NASA, onde havia geometria e resultados divulgados, tornando possível a verificação dos resultados obtidos. Os resultados mostram que as tendências capturadas são condizentes com o esperado, e então com um tempo relativamente baixo, de maneira prática, é possível a previsão do ruído de interação e sua propagação em dutos nos motores turbofans. / The major noise source in aircraft is the engine. Since tonal noise control is well developed, the current effort concentrates on broadband noise reduction, which is less understood. The broadband noise is generated when a turbulent flow interacts with a surface as, for example, rotor blade tip flow, boundary layer and the rotor interaction. Although there are different sources of broadband noise it is known that the major broadband source in turbofan engine is the rotor turbulent wake interacting with the stator vanes. This study is focused in that source of noise and the goal is to develop a model capable of predicting the rotor/stator interaction noise as well as in duct noise propagation. Noise prediction can be carried out by analytical, numerical or empirical methods, each one with advantages and disadvantages. In the present work the semi-analytical method was used. Turbulence characteristics were estimated by a numerical method and the noise generation and duct propagation was estimated by an analytical method. The biggest advantage comparing with the numerical methods is that this method is less time consuming. A purely analytical method would require excessive geometric simplification. The ANCF, a rig developed by NASA was used as basis for the simulations, since its geometry and noise data are available. The results show that the correct trends are consistently captured. So it is concluded that it is possible to predict the broadband noise and its propagation in turbofans engines with a practical and low cost method.
10 July 2012
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.
Lucas, James Redmond
26 June 2013
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. <br /><br />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.<br /> / Master of Science
Allen, Matthew Paul
07 June 2012
Community noise impact is an important factor in design of current generation aircraft, especially when considering projected trends in flight volume and urbanization. Simulation is a useful tool to evaluate the human annoyance response due to both current and proposed aircraft, and it has some advantages over field studies or playback of recordings. However, current simulation methods which are based on time-averaged prediction methods do not include short term fluctuations observed in recordings of real aircraft engines. Those fluctuations in both tonal and broadband sources provide psychoacoustic clues to listeners when evaluating flyover noise realism. When those short-term fluctuations are not included, simulation realism may suffer and evaluation results might not be applicable to real aircraft. This thesis presents work to analyze and model fluctuations in aircraft engine fan noise, using an existing set of static turbofan engine recordings. The inclusion of the observed fluctuations, which are unaccounted for in many current prediction and simulation routines, was expected to increase the perceived realism of simulated flyover events. The analysis of tonal fluctuations was performed by utilizing the complex-valued analytic signal to extract instantaneous amplitude and frequency. A simple parametric model was developed to represent each measured fluctuation using its spectral bandwidth and variance. The model was then used to generate new fluctuations which were perceptually similar to the original. Tonal synthesis was performed as the sum of many amplitude- and frequency-modulated tones. Analysis was also performed on the broadband fan noise component, which used output from the Short-Time Fourier Transform was used to characterize fluctuations in third-octave band SPL. Those fluctuations were not modeled as in the case of tonal fluctuations and were directly reproduced using an overlap-add synthesis tool. A subjective listening test was then conducted to evaluate the perceptual similarity between synthesized and recorded fan noise. That test concluded that synthesized tonal noise which included short-term fluctuations was perceived as more realistic than noise without. It also concluded that the addition of broadband fan noise components tended to mask tonal fluctuations. / Master of Science
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