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Many of the challenges that limited aero-engine operation in the 1950s, 60s, 70s and 80s were static in nature: hot components exceeding temperature margins, stresses in the high-speed rotating structure approaching safety limits,...
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Many of the challenges that limited aero-engine operation in the 1950s, 60s, 70s and 80s were static in nature: hot components exceeding temperature margins, stresses in the high-speed rotating structure approaching safety limits, and turbomachinery aerodynamic efficiencies missing performance goals. Modeling tools have greatly improved since and have helped enhance jet engine design, largely due to better computers and improved simulations of the fluid flow and supporting structure. The situation is thus different today, where important problems encountered past the design and development phases are dynamic in nature. These can jeopardize engine certification and lead to major delays and increased program cost. A real challenge is the characterization of damping and the related dynamic behavior of rotating and stationary components and assemblies, and of the fluid-structure interactions and coupling. The theme of this lecture is instability in the broadest sense. A number of problems of technological interest in aero-engines are discussed with focus on dynamical system modeling and identification of the underlying mechanisms. Future perspectives on outstanding seminal problems and grand challenges are also given.
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Given the maturity of the gas turbine engine since its invention and also considering the limited and flattened level of resources expected to be allocated for NASA aeronautics research and development, we ask the question are NAS...
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Given the maturity of the gas turbine engine since its invention and also considering the limited and flattened level of resources expected to be allocated for NASA aeronautics research and development, we ask the question are NASA technology investments still needed to enable future turbine engine-based propulsion systems? If so, what is NASA's unique role to justify NASA's investment? To address this topic, we will first review the accomplishments and the impact that NASA Glenn Research Center has made on turbine engine technologies over the last 78 years. Specifically, this paper discusses NASA's role and contributions to turbine engine development, specific to both 1) NASA's role in conducting experiments to understand flow physics and provide relevant benchmark validation experiments for Computational Fluid Dynamics (CFD) code development, validation, and assessment; and 2) the impact of technologies resulting from NASA collaborations with industry, academia, and other government agencies. Note that the scope of the discussion is limited to the NASA technology contributions with which the author was intimately associated, and does not represent the entirety of the NASA contributions to turbine engine technology. The specific research, development, and demonstrations discussed herein were selected to both 1) provide a comprehensive review and reference list of the technology and its impact, and 2) identify NASA's unique role and highlight how NASA's involvement resulted in additional benefit to the gas turbine engine community. Secondly, we will discuss current NASA collaborations that are in progress and provide a status of the results. Finally, we discuss the challenges anticipated for future turbine engine-based propulsion systems for civil aviation and identify potential opportunities for collaboration where NASA involvement would be beneficial. Ultimately, the gas turbine engine community will decide if NASA involvement is needed to contribute to the development of the design and analysis tools, databases, and technology demonstration programs to meet these challenges for future turbine engine-based propulsion systems.
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Effects of SDBD and DBD-VGs plasma actuations on film cooling performance of a plain wall were numerically investigated based on the RANS solutions and linearized body force model. With a user defined function (UDF), the plasma ac...
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Effects of SDBD and DBD-VGs plasma actuations on film cooling performance of a plain wall were numerically investigated based on the RANS solutions and linearized body force model. With a user defined function (UDF), the plasma actuation forces were implemented into the momentum equations as the source terms in the commercial CFD solver ANSYS Fluent. With the experiment data and referenced numerical results, reliabilities of the linearized body force model and numerical methods were validated. At a range of dimensionless actuation strengths and frequencies, the film cooling effectiveness on the wall surface and flow structure development in the near-wall regions were analyzed and compared with the plasma-off case. The results show that both SDBD and DBD-VGs plasma actuations are beneficial for reducing the development of kidney vortex pair downstream of the cooling hole, thus significantly improving the film cooling effect on the wall surface. With SDBD plasma actuation, the streamwise velocity gradient in near-wall region is increased compared with the plasma-off case, resulting in delayed coolant flow lifting-off downstream of the cooling hole. However, with DBD-VGs plasma actuation, the development of anti-kidney vortex pair is intensified, which in turn weakens the development of kidney vortex pair and widens the coolant coverage on the wall surface along lateral direction. As the actuation strength and frequency increase, the film cooling effectiveness on the wall surface is enhanced along both streamwise and lateral directions. Compared with the plasma-off case, the area-averaged film cooling effectiveness for DBD-VGs plasma actuation case is increased by 331% at dimensionless actuation frequency of 2.5 and dimensionless actuation strength of 30, whereas for SDBD plasma actuation case the area-averaged film cooling effectiveness is only increased by 42.8% at dimensionless actuation frequency of 2.5 and dimensionless actuation strength of 60. With the same actuation parameters, compared against the SDBD case, a higher film cooling effectiveness is achieved on wall surface for the DBD-VGs plasma actuation case, and the coolant coverage along the lateral direction is significantly improved by DBD-VGs plasma actuation.
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The utilization of automotive engine components for the development of a reverse Brayton cycle is shown in this study. The well-known characteristics of turbochargers and electrical centrifugal compressors commonly used in the aut...
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The utilization of automotive engine components for the development of a reverse Brayton cycle is shown in this study. The well-known characteristics of turbochargers and electrical centrifugal compressors commonly used in the automotive industry is a starting point for developing an experimental cycle configuration of a reverse Brayton refrigeration cycle with the ability to achieve up to 115K after a multi-stage compression with intermediate cooling and a single-stage expansion in a radial turbine using air (R-729) as working fluid. The use of a variable nozzle turbine allows to evaluate the optimum rack position for each operating point, as well as having control over refrigeration capacity. Studies over the minimum cycle pressure at the inlet of the first stage of compression have been performed to assess the possible benefit of creating vacuum or pressurize the working fluid. A 1m~3 cooling chamber was attached to the installation to test the ability of cooling different thermal loads working under different operation ways, open or closed cycle, this is, letting the working fluid to interact with the thermal load or cooling it through a heat exchanger.The evaluation of thermodynamic parameters allows to obtain the coefficient of performance (COP) of the installation as well as the efficiency of each component. The analysis of turbomachinery performance will allow identifying weak points to improve cycle performance, and to improve the coupling model between the rotatory machines as well as to adapt the size of the installation to the refrigeration capacity required for different applications.
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Synchronous motor driven centrifugal compressors are widely used in the oil and gas industry. In evaluating the optimum selection of synchronous motor drivers for centrifugal compressors, it is important to understand the factors ...
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Synchronous motor driven centrifugal compressors are widely used in the oil and gas industry. In evaluating the optimum selection of synchronous motor drivers for centrifugal compressors, it is important to understand the factors influencing a proper match for a centrifugal compressor and its synchronous motor driver. The buyer should specify process requirements and define possible operating scenarios for the entire life of the motor driven centrifugal compressor train. The compressor designer will use the buyer-specified process conditions to model the aero-thermodynamic behavior of the compressor and characterize its performance. Performance, controllability, starting capabilities as well as the optimum power margin required for a future-oriented design must also be considered. This paper reviews the criteria for evaluating the optimal combination of a centrifugal compressor and its synchronous motor driver as an integral package. It also addresses API standard requirements on synchronous motor driven centrifugal compressors. Design considerations for optimal selection and proper sizing of compressor drivers include large starting torque requirements to enable compressor start from settle-out conditions and to prevent flaring are addressed. Start-up capabilities of the motor driver can significantly impact the reliability and operability of the compressor train. API 617 on centrifugal compressors refers to API 546 for synchronous motor drivers. In this paper, requirements of API 617 and 546 are reviewed and several important design and sizing requirements are presented. In the effort to optimize plant design, and maintain the performance requirements, the paper discusses optimization options, such as direct on-line starting method to explore the motor rating limits, and the use of synchronous motors for power factor correction to eliminate or reduce the need for reactive power compensation by capacitor banks. This paper presents a novel approach to show constant reactive power lines on traditional V curves. It also complements capability curves of synchronous motors with lines of constant efficiency. The paper discusses variable frequency drive options currently used for synchronous motors in compressor applications. The paper addresses the available variable frequency drive types, their impact on the electrical grid, and motor design considerations with a view to summarizing factors important to the selection of variable frequency drives.
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Fouling affects gas turbine operation and airborne or fuel contaminants, under certain conditions, become very likely to adhere to surfaces if impact takes place. Particle sticking implies the change in shape in terms of roughness...
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Fouling affects gas turbine operation and airborne or fuel contaminants, under certain conditions, become very likely to adhere to surfaces if impact takes place. Particle sticking implies the change in shape in terms of roughness of the impinged surface. The consequences of these deposits could be dramatic: these effects can shut an aircraft engine down or derate a land-based power unit. This occurrence may happen due to the reduction of the compressor flow rate and the turbine capacity, caused by a variation in the HPT nozzle throat area (geometric blockage due to the thickness of the deposited layer and the aerodynamic blockage due to the increased roughness, and in turn boundary layer). Several methods to quantify particle sticking have been proposed in literature so far, and the experimental data used for their validation vary in a wide range of materials and conditions. The experimental analyses have been supported by (and have given inspiration to) increasingly realistic mathematical models. Experimental tests have been carried out on (ⅰ) a full scale gas turbine unit, (ⅱ) wind tunnel testing or hot gas facilities using stationary cascades, able to reproduce the same conditions of gas turbine nozzle operation and finally, (ⅲ) wind tunnel testing or hot gas facilities using a coupon as the target. In this review, the whole variety of experimental tests performed is gathered and classified according to composition, size, temperature and particle impact velocity. Using particle viscosity and sticking prediction models, over seventy (70) tests are compared with each other and with the model previsions providing a useful starting point for a comprehensive critical analysis. Due to the variety of test conditions, the related results are difficult to be pieced together due to differences in particle material and properties. The historical data of particle deposition obtained over thirty (30) years are classified using particle kinetic energy and the ratio between particle temperature and its softening temperature. Qualitative thresholds for the distinction between particle deposition, surface erosion and particle break-up, based on particle properties and impact conditions, are identified. The outcome of this paper can be used for further development of sticking models or as a starting point for new insight into the problem.
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To enhance worldwide environmental conditions, the air transport industry must drastically reduce carbon dioxide emissions. Electrification of aircraft propulsion systems is one way to meet this demand. In particular, the focus is...
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To enhance worldwide environmental conditions, the air transport industry must drastically reduce carbon dioxide emissions. Electrification of aircraft propulsion systems is one way to meet this demand. In particular, the focus is on obtaining single-aisle aircraft with partial turboelectric propulsion and approximately 150 passenger seats by the 2030s. To develop a single-aisle aircraft with partial turboelectric propulsion, an air-cooled interior permanent magnet (IPM) motor with an output of 2 MW is desired. One of the most difficult problems in air cooling is that air-cooling performance decreases with increasing altitude because the air density decreases. To investigate the effect of altitude on air-cooling performance in the IPM motor, the authors formulated mathematical system equations to describe heat transfer inside the target air-cooled IPM motor, and mathematical analytical solutions were obtained. The most severe condition is the top-of-climb condition. For this condition, a designer should choose cooling air mass flow rates that keep the temperature of the permanent magnets below the maximum temperature limit of 100 ℃ and the temperature of the coils below the maximum temperature limit of 250 ℃. Here, the sizes of the air-cooling channels strongly affect air cooling with the IPM motor. In this paper, the authors briefly review the mathematical formulations and their solutions, investigate the effect of channel size on air-cooling performance in an IPM motor, and explore the optimum configuration and settings for the air cooling channels.
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Liquid fuel jet in Crossflow (LJIC) is significant to the aviation industry since it is a vital technique for atomization. The hydrodynamic instability mechanisms that drive a transverse jet's primary breakup were investigated usi...
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Liquid fuel jet in Crossflow (LJIC) is significant to the aviation industry since it is a vital technique for atomization. The hydrodynamic instability mechanisms that drive a transverse jet's primary breakup were investigated using modal and traveling wavelength analysis. This study highlights the primary breakup mechanisms for aviation fuel Jet-A. However, the techniques discussed are applicable to any liquid. Mathematical decomposition techniques are known as POD (Proper Orthogonal Decomposition), and MrDMD (Multi-Resolution Dynamic Mode Decomposition) are used together to identify dominant instability flow dynamics associated with the primary breakup mechanism. Implementation of the MrDMD method deconstructs the nonlinear dynamical systems into multiresolution time-scaled components that capture the intermittent coherent structures. The MrDMD, in conjunction with the POD method, is applied to data points taken across the entire spray breakup regimes, which are: enhanced capillary breakup, bag breakup, nultimode breakup, and shear breakup. The dominant frequencies of both breakup regimes are extracted and identified. These coherent structures are classified with an associated time scale and Strouhal number. Characterization of the traveling column and surface wavelengths are conducted and associated with a known instability model. It is found that the Plateau -Rayleigh instability model predicts columns wavelengths similar to wavelengths found in dominant modes associated with a capillary breakup. Rayleigh Taylor's instability model matches well with bag and multimode breakup. Small scale surface wavelengths associated with a shear breakup are correlated to a modified Rayleigh Taylor instability model founded by Wang et al. . Furthermore, an atomization model that predicts the Sauter Mean Diameter associated with the dominant small-scale surface traveling wavelengths is established.
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Breaking down the total loss in a turbomachine into a number of low order physical models is a powerful way of developing loss models. A problem, however, is that in complex flows it is often not clear how to put together these ph...
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Breaking down the total loss in a turbomachine into a number of low order physical models is a powerful way of developing loss models. A problem, however, is that in complex flows it is often not clear how to put together these physical models in the correct way. An additional problem is that the designer often doesn 't know whether all of the underlying low order physical models are correct or whether a more general, and accurate, physical model is yet to be discovered. In practice this problem often leads to loss models of low accuracy, which only work in a limited part of the overall design space. This paper shows that machine learning can be used to augment a designer in the process of developing loss models for complex flows. It is shown that it helps both in understanding how to put together the underlying physical models in a more accurate way, and also in discovering new, and more general, underlying physical models. The paper illustrates the new method using the problem of compressor and turbine profile loss. This problem was chosen because it is well understood and therefore is a good way of validating the new method. However, surprisingly the new method is shown to be able to develop a new profile loss model which is more accurate than previous models. This is shown to have been achieved by the machine learning finding a new, more general, underlying model for trailing edge mixing loss.
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Recent developments in Pressure Gain Combustion (PGC) technology have demonstrated its ability to achieve higher thermal efficiencies and lower carbon emissions as compared to conventional gas turbine counterpart working in Brayto...
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Recent developments in Pressure Gain Combustion (PGC) technology have demonstrated its ability to achieve higher thermal efficiencies and lower carbon emissions as compared to conventional gas turbine counterpart working in Brayton cycle. Ongoing studies suggest the possibility of implementing PGC in aircraft engines by replacing the high-pressure section (HP compressor, combustion chamber and HP turbine) with a PGC system. This, coupled with research on advanced materials and cooling solutions, offers the potential for higher overall gas turbine efficiency and fuel economy, contributing towards emission reduction of the aviation sector.This paper aims at a comprehensive review of PGC technology solutions applied in the area of aero propulsion. Reported background covers the historic as well as ongoing research activities at the component level, the cycle level, and the propulsion application of Pulse Detonation Engine (PDE), Rotating Detonation Engine (RDE), Oblique Detonation Wave Engine (ODWE), Free Piston Composite Cycle Engine (FP-CCE), and wave rotor engines. The analytical, numerical, and experimental research work is reviewed, providing also a comparison of PGC engine conceptual designs with existing gas turbine engines used in aerospace propulsion.
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