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1.
  • Wadekar, Sandip, 1989 (author)
  • Large-Eddy Simulation of Gasoline Fuel Spray Injection at Ultra-High Injection Pressures
  • 2021
  • Doctoral thesis (other academic/artistic)abstract
    • Gasoline direct injection is a state-of-the-art technique that reduces hydrocarbon and particulate emissions. However, further improvement is needed to meet current as well as future emission regulations. A prominent solution is to increase the fuel injection pressure which allows faster fuel droplet atomization, quick evaporation and improves fuel-air mixture formation under realistic engine conditions. In this work, the gasoline fuel injection process at ultra-high injection pressures ranging from 200 to 1500 bar was analyzed using numerical models. In particular, the Large-Eddy Simulation (LES) method, with the standard Smagorinsky turbulence model, was utilized using the Eulerian formulation  for the continuous phase. The discrete droplet phase was treated using a Lagrangian formulation together with spray sub-models. In the first part of study, spray was injected into an initially quiescent constant volume chamber using two different nozzle hole shape geometries: divergent and convergent. The numerical results were calibrated by reproducing experimentally observed liquid penetration length and efforts were made to understand the influence of ultra-high injection pressures on spray development. The calibrated models were then used to investigate the impact of ultra-high injection pressures on mean droplet sizes, droplet size distribution, spray-induced large-scale eddies and entrainment rate. The results showed that, at ultra-high injection pressures, the mean droplet sizes were significantly reduced and the droplets achieving very high  velocities. Integral length scales of spray-induced turbulence and air entrainment rate were better for the divergent-shaped injector, and considerably larger at higher injection pressures compared to lower ones. In the second part of the study, four consecutive full-cycle cold flow LES simulations were carried out to generate realistic turbulence inside the engine cylinder. The first three cycles were ignored, with the fourth cycle being used to model the injection of the fuel using the divergent-shaped injector only (which was found to be better in the previous part of this study) at different injection pressures. In addition to the continuous gas phase (Eulerian) and the dispersed liquid (Lagrangian), the liquid film feature (Finite-Area) was used to model the impingement of fuel spray on the engine walls and subsequent liquid film formation. The simulation results were used to evaluate spray-induced turbulence, fuel-air mixing efficiency and the amount of liquid mass deposited on the walls. The limitation of the high-pressure injection technique with respect to liquid film formation was optimized using a start of injection (SOI) sweep. Overall results showed that the mixing efficiency increased at high injection pressure and that SOI should occur between early injection and late injection to optimize the amount of mass being deposited on the engine walls.
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3.
  • Etikyala, Sreelekha, 1991 (author)
  • Particulate Formation in GDI Engines
  • 2022
  • Doctoral thesis (other academic/artistic)abstract
    • The need to comply with stringent emission regulations while improving fuel economy and reducing criteria pollutant emissions from transportation presents a major challenge in the design of gasoline Direct Injection (DI) engines because of the adverse effects of ultrafine Particulate Number (PN) emissions on human health and other environmental concerns. With upcoming advances in vehicle electrification, it may be the case that electric vehicles completely replace all current vehicles powered by internal combustion engines ensuring zero emissions. In the meantime, Gasoline Direct Injection (GDI) engines have become the primary mode of transportation using gasoline as they offer better fuel economy while also providing low CO2 emissions. However, GDI engines tend to produce relatively high PN emissions when compared to conventional Port Fuel Injection (PFI) engines, largely because of challenges associated with in-cylinder liquid fuel injection. Cold-starts, transients, and high load operation generate a disproportionate share of PN emissions from GDI engines over a certification cycle. The mechanisms of PN formation during these stages must therefore be understood to identify solutions that reduce overall PN emissions in order to comply with increasingly strict emissions standards. This work presents experimental studies on particulate emissions from a naturally aspirated single cylinder metal gasoline engine run in a homogeneous configuration. The engine was adapted to enable operation in both DI and PFI modes. In PFI mode, injection was performed through a custom inlet manifold about 50 cm from the cylinder head to maximize the homogeneity of the fuel-air mixture. The metal head was eventually modified by incorporating an endoscope that made it possible to visualize the combustion process inside the cylinder. The experimental campaigns were structured to systematically isolate and clarify PN formation mechanisms. Tests were initially performed in steady state mode to obtain preliminary insights and to screen operating conditions before conducting transient tests. Particulate emissions were measured and correlated with the images obtained through endoscope visualization where possible. Key objectives of these studies were to find ways of reducing PN formation by increasing combustion stability. It was found that by avoiding conditions that cause wall wetting with liquid fuel, PN emissions can be substantially reduced during both steady state operation and transients. Warming the coolant and injecting fuel at later timings reduced PN emissions during warmup and cold transient conditions. Additionally, experiments using fuel blends with different oxygenate contents showed that the chemical composition of the fuel strongly influences particulate formation under steady state and transient conditions, and that this effect is load-dependent. Overall, the results obtained in this work indicate that wall wetting is the dominant cause of particulate formation inside the cylinder and that fuel-wall interactions involving the piston, cylinder walls, and valves during fuel injection account for a significant proportion of PN emissions in the engine raw exhaust.
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4.
  • Lejon, Marcus, 1986, et al. (author)
  • Multidisciplinary Design of a Three Stage High Speed Booster
  • 2017
  • In: ASME Turbo Expo 2017: Turbine Technical Conference and Exposition. - : ASME Press. ; 2B-2017
  • Conference paper (peer-reviewed)abstract
    • The paper describes a multidisciplinary conceptual design of an axial compressor, targeting a three stage, high speed, high efficiency booster with a design pressure ratio of 2.8. The paper is outlined in a step wise manner starting from basic aircraft and engine thrust requirements, establishing the definition of the high speed booster interface points and its location in the engine. Thereafter, the aerodynamic 1D/2D design is carried out using the commercial throughflow tool SC90C. A number of design aspects are described, and the steps necessary to arrive at the final design are outlined. The SC90C based design is then carried over to a CFD based conceptual design tool AxCent, in which a first profiling is carried out based on a multiple circular arc blade definition. The design obtained at this point is referred to as the VINK compressor. The first stage of the compressor is then optimized using an in-house optimization tool, where the objective functions are evaluated from detailed CFD calculations. The design is improved in terms of efficiency and in terms of meeting the design criteria put on the stage in the earlier design phases. Finally, some aeromechanical design aspects of the first stage are considered. The geometry and inlet boundary conditions of the compressor are shared with the turbomachinery community on a public server. This is intended to be used as a test case for further optimization and analysis.
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5.
  • Okda, Sherif, et al. (author)
  • Testing of the Aerodynamic Characteristics of an Inflatable Airfoil Section
  • 2020
  • In: Journal of Aerospace Engineering. - 1943-5525 .- 0893-1321. ; 33:5
  • Journal article (peer-reviewed)abstract
    • Inflatable structures are characterized by being light and easy to manufacture and deploy. Hence, they find many applications in aerospace and aeronautical engineering. In this paper, an inflatable segment with a The National Advisory Committee for Aeronautics (NACA) 0021 airfoil cross-section is designed, fabricated, and tested. The geometrical accuracy of the manufactured inflatable segment is measured using laser scanning. Measurements show that the average normalized error of the chord length and thickness are 2.97% and 0.554%, respectively. The aerodynamic behavior of the inflatable segment is then tested in a wind tunnel at different wind speeds and angles of attack. Lift forces are measured using a six-component balance, while the drag forces are calculated from the wake measurements. The lift and drag coefficients of the inflatable section are compared to those of a standard NACA 0021 airfoil. Finally, flow visualization is examined at different angles of attack using two methods: smoke and tufts. Both methods show that flow separation starts at 15° and full stall occurs at 25°. Results indicate that inflatables can find more applications in the design and construction of aerodynamic structures, such as wings.
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6.
  • Li, Xiaojian, 1991, et al. (author)
  • Installation effects on engine design
  • 2020
  • Conference paper (other academic/artistic)abstract
    • Increasing the engine bypass ratio is one way to improve propulsive efficiency. However, an increase in the bypass ratio (BPR) has usually been associated with an increase in the fan diameter. Consequently, there can be a notable increase in the impact of the engine installation on the overall aircraft performance. In order to achieve a better balance between those factors, it requires novel nacelle and engine design concepts. This report mainly reviews installation effects on engine design. Firstly, the installation effects assessment methods are introduced. Then, the installation effects on engine cycle design, intake design and exhaust design are sequentially reviewed.
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7.
  • Pieringer, Astrid, 1979, et al. (author)
  • Investigation of railway curve squeal using a combination of frequency- and time-domain models
  • 2016
  • In: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16. ; , s. 444 - 451
  • Conference paper (peer-reviewed)abstract
    • Railway curve squeal arises from self-excited vibrations during curving. In this paper, a frequency- and a timedomainapproach for curve squeal are compared. In particular, the capability of the frequency-domain model topredict the onset of squeal and the squeal frequencies is studied. In the frequency-domain model, linear stabilityis investigated through complex eigenvalue analysis. The time-domain model is based on a Green's functionsapproach and uses a convolution procedure to obtain the system response. To ensure comparability, the samesubmodels are implemented in both squeal models. The structural flexibility of a rotating wheel is modelled byadopting Eulerian coordinates. To account for the moving wheel‒rail contact load, the so-called moving elementmethod is used to model the track. The local friction characteristics in the contact zone is modelled inaccordance with Coulomb's law with a constant friction coefficient. The frictional instability arises due togeometrical coupling. In the time-domain model, Kalker's non-linear, non-steady state rolling contact modelincluding the algorithms NORM and TANG for normal and tangential contact, respectively, is solved in eachtime step. In the frequency-domain model, the normal wheel/rail contact is modelled by a linearization of theforce-displacement relation obtained with NORM around the quasi-static state and full-slip conditions areconsidered in tangential direction. Conditions similar to those of a curve on the Stockholm metro exposed tosevere curve squeal are studied with both squeal models. The influence of the wheel-rail friction coefficient andthe direction of the resulting creep force on the occurrence of squeal is investigated for vanishing train speed. Results from both models are similar in terms of the instability range in the parameter space and the predictedsqueal frequencies.
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8.
  • Hadadpour, Ahmad (author)
  • Spray combustion with multiple-injection in modern engine conditions
  • 2020
  • Doctoral thesis (other academic/artistic)abstract
    • Combustion of fuel in diesel engines emits substances harmful to the environment such as soot. These emissions can be reduced by either in-cylinder treatments or after-treatments. One of the common in-cylinder treatments is multiple-injection, which divides a single fuel injection to multiple smaller injections. There are many open questions on the physical processes of the ignition, combustion and emissions of diesel spray flame with multiple injections. The current PhD project aims at studying these processes using large-eddy simulations (LES) and strives to answer some of the open questions. To develop a fast and robust LES tool for this study, a new method is formulated for spray combustion simulation. This method is developed based on the flamelet-generated manifold (FGM) method and the Eulerian stochastic fields (ESF) method. The new ESF/FGM method relaxes some of the substantial assumptions in conventional FGM, while it still keeps the computational costs at a reasonable level for engineering applications. Additionally in this work, a new reaction progress variable for FGM models is proposed by using local oxygen consumption, and the advantages and limitations of this progress variable are explored. Spray-A from Engine Combustion Network (ECN) which is designed to mimic modern engine conditions is chosen as the baseline case for simulations. In this case, liquid n-dodecane, which is a diesel surrogate, is injected into a high-pressure constant-volume vessel. The comparison of simulation results with experimental measurements shows that the ESF/FGM method with the new progress variable can predict the spray combustion characteristics such as ignition delay time, ignition location, lift-off length, pressure rise and thermochemical structure of the spray flame, accurately. After validation of simulation results against experimental measurements, the new ESF/FGM and other available turbulence-combustion simulation tools are applied to simulate multiple-injection spray combustion. Different multiple-injection strategies are investigated by systematically changing the injection timing. The effects of applying each strategy on the ignition, combustion, mixing and emissions are investigated. The results show that in split-injection and post-injection strategies the major physical reason for reduction of soot is better air entrainment and lower local equivalence ratio. It is shown that increasing the dwell time and retarding it toward the end of injection can enhance this effect. On the contrary, for the pre-injection strategies, shortening the ignition delay time of the main injection reduces its pre-mixing and increases its soot formation. In these strategies, the high-temperature region from the pre-injection combustion can increase soot oxidation of the main injection fuel, only if this region is not cooled down as a result of air entrainment during dwell time. Therefore, in such cases shortening the dwell time decreases net soot emissions.
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9.
  • Kyprianidis, Konstantinos, 1984, et al. (author)
  • Multidisciplinary Analysis of a Geared Fan Intercooled Core Aero-Engine
  • 2014
  • In: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 136:1
  • Journal article (peer-reviewed)abstract
    • The reduction of CO2 emissions is strongly linked with the improvement of engine specific fuel consumption, along with the reduction of engine nacelle drag and weight. One alternative design approach to improving specific fuel consumption is to consider a geared fan combined with an increased overall pressure ratio intercooled core performance cycle. The thermal benefits from intercooling have been well documented in the literature. Nevertheless, there is very little information available in the public domain with respect to design space exploration of such an engine concept when combined with a geared fan. The present work uses a multidisciplinary conceptual design tool to analyze the option of an intercooled core geared fan aero engine for long haul applications with a 2020 entry into service technology level assumption. With minimum mission fuel in mind, the results indicate as optimal values a pressure ratio split exponent of 0.38 and an intercooler mass flow ratio of 1.18 at hot-day top of climb conditions. At ISA midcruise conditions a specific thrust of 86 m/s, a jet velocity ratio of 0.83, an intercooler effectiveness of 56%, and an overall pressure ratio value of 76 are likely to be a good choice. A 70,000 lbf intercooled turbofan engine is large enough to make efficient use of an all-axial compression system, particularly within a geared fan configuration, but intercooling is perhaps more likely to be applied to even larger engines. The proposed optimal jet velocity ratio is actually higher than the value one would expect by using standard analytical expressions, primarily because this design variable affects core efficiency at midcruise due to a combination of several different subtle changes to the core cycle and core component efficiencies at this condition. The analytical expressions do not consider changes in core efficiency and the beneficial effect of intercooling on transfer efficiency, nor do they account for losses in the bypass duct and jet pipe, while a relatively detailed engine performance model, such as the one utilized in this study, does. Mission fuel results from a surrogate model are in good agreement with the results obtained from a rubberized-wing aircraft model for some of the design parameters. This indicates that it is possible to replace an aircraft model with specific fuel consumption and weight penalty exchange rates. Nevertheless, drag count exchange rates have to be utilized to properly assess changes in mission fuel for those design parameters that affect nacelle diameter.
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10.
  • Thulin, Oskar, 1987, et al. (author)
  • First and Second Law Analysis of Radical Intercooling Concepts
  • 2018
  • In: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 140:8, s. 081201-081201-10
  • Journal article (peer-reviewed)abstract
    • An exergy framework was developed taking into consideration a detailed analysis of the heat exchanger (HEX) (intercooler (IC)) component irreversibilities. Moreover, it was further extended to include an adequate formulation for closed systems, e.g., a secondary cycle (SC), moving with the aircraft. Afterward, the proposed framework was employed to study two radical intercooling concepts. The first proposed concept uses already available wetted surfaces, i.e., nacelle surfaces, to reject the core heat and contributes to an overall drag reduction. The second concept uses the rejected core heat to power a secondary organic Rankine cycle and produces useful power to the aircraft-engine system. Both radical concepts are integrated into a high bypass ratio (BPR) turbofan engine, with technology levels assumed to be available by year 2025. A reference intercooled cycle incorporating a HEX in the bypass (BP) duct is established for comparison. Results indicate that the radical intercooling concepts studied in this paper show similar performance levels to the reference cycle. This is mainly due to higher irreversibility rates created during the heat exchange process. A detailed assessment of the irreversibility contributors, including the considered HEXs and SC, is made. A striking strength of the present analysis is the assessment of the component-level irreversibility rate and its contribution to the overall aero-engine losses.
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11.
  • Thulin, Oskar, 1987 (author)
  • On the Analysis of Energy Efficient Aircraft Engines
  • 2017
  • Doctoral thesis (other academic/artistic)abstract
    • Aero engine performance analysis is highly multidimensional using various measures of component performance such as turbomachinery and mechanical efficiencies, and pressure loss coefficients. Using conventional performance analysis, relying on only the laws of thermodynamics, it is possible to understand how the performance parameters affect the component performance, but it is difficult to directly compare the magnitude of various loss sources. A comprehensive framework has been detailed to analyze aero engine loss sources in one common currency. As the common currency yields a measure of the lost work potential in every component, it is used to relate the component performance to the system performance. The theory includes a more detailed layout of all the terms that apply to a propulsion unit than presented before. The framework is here adopted to real gases to be used in state of the art performance codes. Additionally, the framework is further developed to enable detailed studies of two radical intercooling concepts that either rejects the core heat in the outer nacelle surfaces or uses the core heat for powering of a secondary cycle. The theory is also extended upon by presenting the installed rational efficiency, a true measure of the propulsion subsystem performance, including the installation effects of the propulsion subsystem as it adds weight and drag that needs to be compensated for in the performance assessment.
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13.
  • Li, Xiaojian, 1991, et al. (author)
  • A New Method for Impeller Inlet Design of Supercritical CO2 Centrifugal Compressors in Brayton Cycles
  • 2020
  • In: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:19
  • Journal article (peer-reviewed)abstract
    • Supercritical Carbon Dioxide (SCO2) is considered as a potential working fluid in next generation power and energy systems. The SCO2 Brayton cycle is advantaged with higher cycle efficiency, smaller compression work, and more compact layout, as compared with traditional cycles. When the inlet total condition of the compressor approaches the critical point of the working fluid, the cycle efficiency is further enhanced. However, the flow acceleration near the impeller inducer causes the fluid to enter two-phase region, which may lead to additional aerodynamic losses and flow instability. In this study, a new impeller inlet design method is proposed to achieve a better balance among the cycle efficiency, compressor compactness, and inducer condensation. This approach couples a concept of the maximum swallowing capacity of real gas and a new principle for condensation design. Firstly, the mass flow function of real gas centrifugal compressors is analytically expressed by non-dimensional parameters. An optimal inlet flow angle is derived to achieve the maximum swallowing capacity under a certain inlet relative Mach number, which leads to the minimum energy loss and a more compact geometry for the compressor. Secondly, a new condensation design principle is developed by proposing a novel concept of the two-zone inlet total condition for SCO2 compressors. In this new principle, the acceptable acceleration margin (AAM) is derived as a criterion to limit the impeller inlet condensation. The present inlet design method is validated in the design and simulation of a low-flow-coefficient compressor stage based on the real gas model. The mechanisms of flow accelerations in the impeller inducer, which form low-pressure regions and further produce condensation, are analyzed and clarified under different operating conditions. It is found that the proposed method is efficient to limit the condensation in the impeller inducer, keep the compactness of the compressor, and maintain a high cycle efficiency.
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14.
  • Bayani, Mohsen, 1981 (author)
  • Squeak and Rattle Prediction for Robust Product Development in the automotive industry
  • 2021
  • Doctoral thesis (other academic/artistic)abstract
    • Squeak and rattle are nonstationary, irregular, and impulsive sounds that are audible inside the car cabin. For decades, customer complaints about squeak and rattle have been, and still are, among the top quality issues in the automotive industry. These annoying sounds are perceived as quality defect indications and burden warranty costs to the car manufacturers. Today, the quality improvements regarding the persistent type of sounds in the car, as well as the increasing popularity of electric engines, as green and quiet propulsion solutions, stress the necessity for attenuating annoying sounds like squeak and rattle more than in the past. The economical and robust solutions to this problem are to be sought in the pre-design-freeze phases of the product development and by employing design-concept-related practices. To achieve this goal, prediction and evaluation tools and methods are required to deal with the squeak and rattle quality issues upfront in the product development process. The available tools and methods for the prediction of squeak and rattle sounds in the pre-design-freeze phases of a car development process are not yet sufficiently mature. The complexity of the squeak and rattle events, the existing knowledge gap about the mechanisms behind the squeak and rattle sounds, the lack of accurate simulation and post-processing methods, as well as the computational cost of complex simulations are some of the significant hurdles in this immaturity. This research addresses this problem by identifying a framework for the prediction of squeak and rattle sounds based on a cause-and-effect diagram. The main domains and the elements and the sub-contributors to the problem in each domain within this framework are determined through literature studies, field explorations and descriptive studies conducted on the subject. Further, improvement suggestions for the squeak and rattle evaluation and prediction methods are proposed through prescriptive studies. The applications of some of the proposed methods in the automotive industry are demonstrated and examined in industrial problems. The outcome of this study enhances the understanding of some of the parameters engaged in the squeak and rattle generation. Simulation methods are proposed to actively involve the contributing factors studied in this work for squeak and rattle risk evaluation. To enhance the efficiency and accuracy of the risk evaluation process, methods were investigated and proposed for the system excitation efficiency, modelling accuracy and efficiency and quantification of the response in the time and frequency domains. The demonstrated simulation methods besides the improved understanding of the mechanisms behind the phenomenon can facilitate a more accurate and robust prediction of squeak and rattle risk during the pre-design-freeze stages of the car development.
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15.
  • Gantasala, Sudhakar, et al. (author)
  • Numerical Investigation of the Aeroelastic Behavior of a Wind Turbine with Iced Blades
  • 2019
  • In: Energies. - : MDPI. - 1996-1073. ; 12:12
  • Journal article (peer-reviewed)abstract
    • Wind turbines installed in cold-climate regions are prone to the risks of ice accumulation which affects their aeroelastic behavior. The studies carried out on this topic so far considered icing in a few sections of the blade, mostly located in the outer part of the blade, and their influence on the loads and power production of the turbine are only analyzed. The knowledge about the influence of icing in different locations of the blade and asymmetrical icing of the blades on loads, power, and vibration behavior of the turbine is still not matured. To improve this knowledge, multiple simulation cases are needed to run with different ice accumulations on the blade considering structural and aerodynamic property changes due to ice. Such simulations can be easily run by automating the ice shape creation on aerofoil sections and two-dimensional (2-D) Computational Fluid Dynamics (CFD) analysis of those sections. The current work proposes such methodology and it is illustrated on the National Renewable Energy Laboratory (NREL) 5 MW baseline wind turbine model. The influence of symmetrical icing in different locations of the blade and asymmetrical icing of the blade assembly is analyzed on the turbine’s dynamic behavior using the aeroelastic computer-aided engineering tool FAST. The outer third of the blade produces about 50% of the turbine’s total power and severe icing in this part of the blade reduces power output and aeroelastic damping of the blade’s flapwise vibration modes. The increase in blade mass due to ice reduces its natural frequencies which can be extracted from the vibration responses of the turbine operating under turbulent wind conditions. Symmetrical icing of the blades reduces loads acting on the turbine components, whereas asymmetrical icing of the blades induces loads and vibrations in the tower, hub, and nacelle assembly at a frequency synchronous to rotational speed of the turbine.
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16.
  • Johansson, Anders, 1985, et al. (author)
  • Experimental Investigation of Soot in a Spray-Guided Single Cylinder GDI Engine Operating in a Stratified Mode
  • 2013
  • In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 6
  • Journal article (peer-reviewed)abstract
    • Forthcoming reductions in legal limits for emissions of particle matter (PM) from direct injection engines have increased the need for understanding particle distributions in the engines and the factors affecting them. Therefore, in the presented study the influence on PM-emissions of potentially important factors (fuel injection pressure, load, speed and 50% mass fraction burned phasing) on particle mass, number and size distributions were experimentally investigated. The experimental system was a spray-guided, direct injection, single-cylinder research engine operated in stratified charge mode (using gasoline with 10% ethanol as fuel), under five load and speed settings that are appropriate for stratified combustion. The particle distributions obtained from operating the engine in homogeneous combustion and stratified combustion modes were also compared. The particle distributions were measured using a Cambustion DMS500 fast particle analyzer in combination with a Dekati FPS4000 fine particle sampler and a thermodenuder in all tests except the comparison of distributions under stratified and homogeneous combustion conditions. The sampling system was designed to remove as much of the volatile unburned hydrocarbons as possible in order to sample mostly solid particles. Under all of the stratified operating conditions studied, the results indicate that the particle distribution has a characteristic shape with a tail and one large peak. The operating speed significantly affected the size of the largest particles and the quantity of the particles represented by the tail. An almost linear, positive relationship was found between the load and particle number. Increasing the fuel injection pressure reduced particle numbers whereas combustion phasing had no significant observed effects. More particles were generated in stratified combustion mode than in homogeneous mode.
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17.
  • Cervantes, Michel, et al. (author)
  • Porjus U9A full-scale hydropower research facility
  • 2008
  • In: Hydro technology and the evironment for the new century. - Foz do Iguassu.
  • Conference paper (peer-reviewed)abstract
    • Hydropower still faces complex scientific and technical challenges in order to secure the availability and reliability of the power plants despite more than a century of development. The main challenge is due to new market constrains such as electrical market deregulation and introduction of renewable sources of energy. The major problem is related to the dynamic of the rotor involving several fields: hydraulics, power engineering and mechanics. On the other side, the large and growing hydropower world market represents an opportunity for technically advanced companies offering better efficiency. The difficulty to scale rigorously any technical advance makes full-scale experiment a necessity. World unique facilities are available at Porjus, Sweden, for this purpose. The Porjus Hydropower Centre is composed of a Francis (U8) and a Kaplan (U9) turbine of 10 MW, each exclusively dedicated to education, research and development. In order to further investigate specific issues related to availability and reliability, a project was initiated in 2006. The main objective is to make U9 a full-scale hydropower laboratory able firstly to furnish the necessary data for the development of rotor-dynamic models but also turbines and bearings. To this purposes more than 200 sensors have been installed to measure displacements, forces, pressure, film thickness, strains... The work presents an overview of the newly upgrade facility as well as some of the problems faced during the instrumentation of the machine.
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18.
  • Lundberg, Oskar, 1980- (author)
  • On the influence of surface roughness on rolling contact forces
  • 2016
  • Doctoral thesis (other academic/artistic)abstract
    • Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.
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19.
  • Mill, O., et al. (author)
  • Analysis and development of hydro power research : synthesis within Swedish Hydro Power Centre
  • 2010
  • Reports (other academic/artistic)abstract
    • The market for hydropower re-investments in Sweden is approx 2.5 billion SEK/yr the coming decade. Large investments will also be carried out in Swedish tailing dams. This will result in challenging projects and need of experts. A crucial factor for a successful management of these challenges is the supply of engineers and researchers with hydro power and dam skills and knowledge. Swedish Hydro Power Centre (Svenskt vattenkraftcentrum, SVC) is a competence centre for university education and research environments within hydro power and mining dams. SVC comprises of two knowledge areas: Hydraulic Engineering and Hydro Turbines and Generators, respectively. SVC builds high-quality and long term sustainable knowledge at selected universities...
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20.
  • Torstensson, Peter, 1981, et al. (author)
  • Hybrid model for prediction of impact noise generated at railway crossings
  • 2016
  • In: Proceedings of the 12h International Workshop on Railway Noise (IWRN12), Terrigal, Australia, September 12-16 (2016). ; , s. 539 - 545
  • Conference paper (peer-reviewed)abstract
    • A hybrid model for the prediction of impact noise at railway crossings is presented. The hybrid model combines the simulation of vertical wheel‒rail contact force in the time domain and the prediction of sound pressure level using a linear frequency-domain model. The time-domain model uses moving Green’s functions for the vehicle and track models (accounting for wheel flexibility and a discretely supported rail with space-variant beam properties) and a non-Hertzian wheel‒rail contact model. The time-domain and frequency-domain models are coupled based on the concept of an equivalent roughness spectrum. The model is demonstrated by investigating the influence of axle load, vehicle speed and wheel profile on generated impact noise levels. A negligible influence on impact noise is observed for axle loads in the interval 15 – 25 tonnes. On the other hand, increasing vehicle speed from 80 km/h to 150 km/h, or comparing a nominal S1002 wheel profile with a severely hollow worn profile, result in substantially higher levels of impact noise; for the given wheel and track conditions the differences are in the order of 10 dB(A).
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21.
  • Winroth, Julia, 1981, et al. (author)
  • Contact stiffness considerations when simulating tyre/road noise
  • 2017
  • In: Journal of Sound and Vibration. - : Elsevier BV. - 1095-8568 .- 0022-460X. ; 409, s. 274-286
  • Journal article (peer-reviewed)abstract
    • Tyre/road simulation tools that can capture tyre vibrations, rolling resistance and noise generation are useful for understanding the complex processes that are involved and thereby promoting further development and optimisation. The most detailed tyre/road contact models use a spatial discretisation of the contact and assume an interfacial stiffness to account for the small-scale roughness within the elements. This interfacial stiffness has been found to have a significant impact on the simulated noise emissions but no thorough investigations of this sensitivity have been conducted. Three mechanisms are thought to be involved: The horn effect, the modal composition of the vibrational field of the tyre and the contact forces exciting the tyre vibrations. This study used a numerical tyre/road noise simulation tool based on physical relations to investigate these aspects. The model includes a detailed time-domain contact model with linear or non-linear contact springs that accounts for the effect of local tread deformation on smaller length scales. Results confirm that an increase in contact spring stiffness causes a significant increase of the simulated tyre/road noise. This is primarily caused by a corresponding increase in the contact forces, resulting in larger vibrational amplitudes. The horn effect and the modal composition are relatively unaffected and have minor effects on the radiated noise. A more detailed non-linear contact spring formulation with lower stiffness at small indentations results in a reduced high-frequency content in the contact forces and the simulated noise.
  •  
22.
  • Chernoray, Valery, 1975 (author)
  • Prediction of Laminar-Turbulent Transition on an Airfoil at High Level of Free-Stream Turbulence
  • 2015
  • In: Progress in Flight Physics Vol. 7. - 9785945881655 ; , s. 704-
  • Book chapter (other academic/artistic)abstract
    • Prediction of laminar-turbulent transition at high level of free-stream turbulence in boundary layers of airfoil geometries with external pressure gradient changeover is in focus. The aim is a validation of a transition model for transition prediction in turbomachinery applications. Numerical simulations have been performed by using a transition model by Langtry and Menter for a number of different cases of pressure gradient, at Reynolds number-range, based on the airfoil chord, 50 000 ≤ Re ≤ 500 000 and free-stream turbulence intensities 2 % and 4 %. The validation of the computational results against the experimental data showed good performance of used turbulence model for all test cases.
  •  
23.
  • Chernoray, Valery, 1975 (author)
  • Prediction of Laminar-Turbulent Transition on an Airfoil at High Level of Free-Stream Turbulence
  • 2013
  • In: Proc of EUCASS Conf..
  • Conference paper (peer-reviewed)abstract
    • Prediction of laminar-turbulent transition at high level of free-stream turbulence in boundary layers of airfoil geometries with external pressure gradient changeover is in focus. The aim is a validation of a transition model for transition prediction in turbomachinery applications. Numerical simulations have been performed by using a transition model by Langtry and Menter for a number of different cases of pressure gradient, at Reynolds number-range, based on the airfoil chord, 50 000 ≤ Re ≤ 500 000 and free-stream turbulence intensities 2 % and 4 %. The validation of the computational results against the experimental data showed good performance of used turbulence model for all test cases.
  •  
24.
  • Grönstedt, Tomas, 1970, et al. (author)
  • First and Second Law Analysis of Future Aircraft Engines
  • 2014
  • In: Journal of Engineering for Gas Turbines and Power. - : ASME International. - 1528-8919 .- 0742-4795. ; 136:3
  • Journal article (peer-reviewed)abstract
    • An optimal baseline turbofan cycle designed for a performance level expected to be available around year 2050 is established. Detailed performance data are given in take-off, top of climb, and cruise to support the analysis. The losses are analyzed, based on a combined use of the first and second law of thermodynamics, in order to establish a basis for a discussion on future radical engine concepts and to quantify loss levels of very high performance engines. In light of the performance of the future baseline engine, three radical cycles designed to reduce the observed major loss sources are introduced. The combined use of a first and second law analysis of an open rotor engine, an intercooled recuperated engine, and an engine working with a pulse detonation combustion core is presented. In the past, virtually no attention has been paid to the systematic quantification of the irreversibility rates of such radical concepts. Previous research on this topic has concentrated on the analysis of the turbojet and the turbofan engine. In the developed framework, the irreversibility rates are quantified through the calculation of the exergy destruction per unit time. A striking strength of the analysis is that it establishes a common currency for comparing losses originating from very different physical sources of irreversibility. This substantially reduces the complexity of analyzing and comparing losses in aero engines. In particular, the analysis sheds new light on how the intercooled recuperated engine establishes its performance benefits.
  •  
25.
  • Johansson, Anders, 1985, et al. (author)
  • Experimental Investigation of the Influence of Boost on Combustion and Particulate Emissions in Optical and Metal SGDI-Engines Operated in Stratified Mode
  • 2016
  • In: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 9:2, s. 807-818
  • Journal article (peer-reviewed)abstract
    • Boosting and stratified operation can be used to increase the fuel efficiency of modern gasoline direct-injected (GDI) engines. In modern downsized GDI engines, boosting is standard to achieve a high power output. However, boosted GDI-engines have mostly been operated in homogenous mode and little is known about the effects of operating a boosted GDI-engine in stratified mode.This study employed optical and metal engines to examine how boosting influences combustion and particulate emission formation in a spray-guided GDI (SGDI), single cylinder research engine. The setup of the optical and metal engines was identical except the optical engine allowed optical access through the piston and cylinder liner.The engines were operated in steady state mode at five different engine operating points representing various loads and speeds. The engines were boosted with compressed air and operated at three levels of boost, as well as atmospheric pressure for comparison. The fuel used was market gasoline (95 RON) blended with 10% ethanol. The spark plug and injector were mounted in parallel with the intake valves. The gas motion induced by the engine head was primarily tumble motion with a small amount of swirl.Results on particulate emissions indicated that nucleation mode particulates increased with increasing boost. In contrast, agglomeration mode particulates decreased with increasing boost pressure. The combustion was found to consist of a yellow flame in the center of the combustion chamber and a pre-mixed blue flame in the perimeter. The optical studies indicated that the flame area decreased with increasing boost.
  •  
26.
  • Johansson, Anders, 1985, et al. (author)
  • Measurements of particulate size distribution from a GDI engine using a nafion dryer and a DMS500 without sample dilution
  • 2014
  • In: FISITA 2014 World Automotive Congress - Proceedings.
  • Conference paper (peer-reviewed)abstract
    • Several types of engine exhaust contain moisture that must be maintained in gaseous state when sampling particulates to prevent potential destruction of the particles or damage to the measurement apparatus. This is normally achieved by diluting the sample in order to reduce the partial pressure, thus avoiding condensation. When measuring size distributions of particulates emitted from a gasoline engine, a dilution ratio of at least 5:1 is recommended. However, in some operating modes (e.g. lean homogenous modes) or measurement locations (e.g. downstream of a particulate filter) this ratio can be too high for high-resolution measurements due to the low levels of particulates. The presented study investigates the potential for using a nafion dryer to remove water from the exhaust instead of diluting the sample. An electrical mobility measurement device, a Cambustion DMS500 mk II, was operated without diluting the exhaust gases but with a nafion dryer to remove water from the exhaust. These dryers are commonly used for measuring particulates in airborne aerosols, but no information has been found in the open literature on their application in engine research. The sampling system was connected to a four cylinder SGDI-engine operating in modes that generate small amount of particulates. Samples were taken in four operating conditions, downstream of the catalyst. Overall losses in the complete system and components of the system were determined by tests with an artificially generated aerosol. Factors such as particulate losses, system performance and sample manipulation are discussed. Particulate size distributions were successfully recorded in operating regimes in which they are difficult to measure with conventional sampling systems using the required dilution. Particulate losses were found to be small in the nafion dryer but large in the heated hose prior to the nafion dryer.
  •  
27.
  • Korkmaz, Kadir Burak, 1989 (author)
  • Improved Power Predictions of Ships Using Combined CFD/EFD Methods for the Form Factor
  • 2020
  • Licentiate thesis (other academic/artistic)abstract
    • Performance prediction of a ship is one of the most important tasks during the design phase. Once the design is finalized, the speed attained at a certain power consumption has to be verified with the most accurate prediction as it is specified at the contract of a new ship order and also required by the legal authorities. Considering the current commercial tendencies and the requirements enforced by legal authorities, towing tank testing and the extrapolation methods recommended by the International Towing Tank Conference (ITTC) are used and regarded as a highly accurate power prediction methodology for common cargo vessels. However, some aspects of this methodology have been questioned such as the scale effects on the form factor and its determination method. It is argued in this thesis that if a part of the Experimental Fluid Dynamics (EFD) based measure or the extrapolation procedure causes higher uncertainty than the numerical uncertainty and modelling errors of a Computational Fluid Dynamics (CFD) application, the corresponding part of the performance prediction method can be replaced or supplemented by CFD. In this study, the possibility to improve the power predictions by the introduction of a combined CFD/EFD Method was investigated by replacing the experimental determination of the form factor with double body computations based on the Reynolds-Averaged Navier-Stokes (RANS) equations, i.e. CFD based form factors. As a result of a joint, study where the double body simulations performed with seven different CFD codes, the CFD based form factors compared well with the experimentally determined form factors. Additionally, the standard deviations of the CFD based form factors were similar to the experimental uncertainty of the form factors even though the abundance of unsystematically varied methods and grids. Following the Quality Assurance Procedure proposed by the ITTC, a best practice guideline has been derived for the CFD based form factor determination method by applying systematic variations to the CFD set-ups. After the verification and validation of the CFD based form factor method in model scale, the full scale speed-power-rpm relations between large number of speed trials and full scale predictions were investigated using the CFD based form factors in combination to the ITTC-57 line and the numerical friction lines. It is observed that the usage of CFD based form factors improves the predictions in general and no deterioration in the prediction accuracy is noted within the limits of this study. Therefore, the combination of EFD and CFD is expected to provide immediate improvements to the 1978 ITTC Performance Prediction Method.
  •  
28.
  • Lindgren, Ronny, 1976, et al. (author)
  • Modeling gasoline spray-wall interactions and comparison to experimental data
  • 2004
  • In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627.
  • Journal article (peer-reviewed)abstract
    • The effects of a gasoline spray impinging on a heated surface were investigated under simulated engine conditions in an earlier study. The data from the experimental investigation have now been compared to results obtained from Computational Fluid Dynamic (CFD) simulations generated using several different numerical models for spray-wall impingement found in the literature. It was found that the models based on single-drop experiments do not predict the outcome of spray impingement well in some respects. Their major drawback was that the predicted diameter distributions of the reflected drops in the secondary spray were shifted downwards from the measured drop size distributions. The tested models predicted the normal velocity component relative to the wall well. However, they were less good at capturing the tangential velocity component relative to the wall. Since the models did not capture the velocities in the tangential direction correctly, the spread of the secondary spray above the wall was under-predicted.
  •  
29.
  • Malmek, Karolina, 1990, et al. (author)
  • Rapid aerodynamic method for predicting the performance of interacting wing sails
  • 2024
  • In: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 293
  • Journal article (peer-reviewed)abstract
    • Rapid performance prediction tools are required for the evaluation, optimization, and comparison of different wind propulsion systems (WPSs). These tools should capture viscous aerodynamic flow effects in 3D, particularly the maximum propulsion force, stall angles, and interaction effects between the lift-generating units. This paper presents a rapid aerodynamic calculation method for wing sails that combines a semiempirical lifting line model with a potential flow-based interaction model to account for 3D interaction effects. The method was applied to a WPS that consisted of several wing sails with considerable interaction effects. The results were compared to CFD RANS simulations in 2D and in 3D. For the evaluated validation cases, the interaction model improved the prediction considerably compared to when the interaction was not accounted for. The method provided acceptable driving force, moments, and stall predictions, with negligible computational cost compared to 3D CFD simulations.
  •  
30.
  • Marimon Giovannetti, Laura, et al. (author)
  • Multi-wing sails interaction effects
  • 2022
  • In: SNAME 24th Chesapeake Sailing Yacht Symposium, CSYS 2022. - : The Society of Naval Architects and Marine Engineers.
  • Conference paper (peer-reviewed)abstract
    • The effects of multiple wings interacting and the change in efficiency due to those effects as well as optimal sheeting angles are becoming an important area of study with the advent of wind-propelled ships for goods transport. This research presents a first analysis of wind tunnel tests carried out at the University of Southampton R.J. Mitchell wind tunnel where three wings are subject to turbulent flow with Reynolds number in excess of 1 million. A range of possible variations of ship heading and apparent wind angles are tested taking into consideration the blockage effects and the geometrical characteristics of the working section. The forces and moments are captured on each individual wing as well as in the overall wind tunnel balance with 6-components dynamometers. Furthermore, pressure sensors and PIV data are recorded during the tests to provide the experimental campaign with results that can validate both qualitatively and quantitatively the numerical tools developed to aid the design stage of wind propelled vessels.
  •  
31.
  • Niebles Atencio, Bercelay, 1979, et al. (author)
  • An experimental study on laminar-turbulent transition at high free-stream turbulence in boundary layers with pressure gradients
  • 2012
  • In: The European Physical Journal Conferences. - : EDP Sciences. ; 25, s. Art. no. 01012-
  • Conference paper (peer-reviewed)abstract
    • We report here the results of a study on measurements and prediction of laminar-turbulenttransition at high free-stream turbulence in boundary layers of the airfoil-like geometries with presence of the external pressure gradient changeover. The experiments are performed for a number of flow cases with different flow Reynolds number, turbulence intensity and pressure gradient distributions. The results were then compared to numerical calculations for same geometries and flow conditions. The experiments and computations are performed for the flow parameters which are typical for turbomachinery applications and the major idea of the current study is the validation of the turbulencemodel which can be used for such engineering applications.
  •  
32.
  • Ottersten, Martin, 1981, et al. (author)
  • Inlet Gap Influence on Low-Frequency Flow Unsteadiness in a Centrifugal Fan
  • 2022
  • In: Aerospace. - : MDPI AG. - 2226-4310. ; 9:12
  • Journal article (peer-reviewed)abstract
    • In this study, unsteady low-frequency characteristics in a voluteless low-speed centrifugal fan operating at a high mass flow rate are studied with improved delayed detached eddy simulation (IDDES). This study is motivated by a recent finding that the non-uniformly distributed pressure inside this type of fan could be alleviated by improving the gap geometry. The present simulation results show that the velocity magnitudes of the gap have distinct low and high regions. Intensive turbulent structures are developed in the low-velocity regions and are swept downstream along the intersection between the blade and shroud, on the pressure side of the blade. Eventually, the turbulence gives rise to a high-pressure region near the blade’s trailing edge. This unsteady flow behavior revolves around the fan rotation axis. Additionally, its period is 5% of the fan rotation speed, based on the analysis of the time history of the gap velocity magnitudes and the evolution of the high-pressure region. The same frequency of high pressure was also found in previous experimental measurements. To the authors’ knowledge, this is the first time that the trigger of the gap turbulence, i.e., the unsteady local low velocity, has been determined.
  •  
33.
  • Ottersten, Martin, 1981 (author)
  • Numerical investigation of tonal noise sources from centrifugal fan
  • 2020
  • Licentiate thesis (other academic/artistic)abstract
    • Heating, ventilating, and air conditioning systems (HVAC) are today an important part of many people's life. They provide a sufficient amount of airflow with the correct temperature, quality, and humidity. The negative side is the noise it produces. Many improvements have been made in building development to reduce noise from the environment. When so, the noise from the HVAC system becomes clearer. The dominant tonal noise in an HVAC system is produced by the fan. In this work tonal noises produced by a centrifugal fan is investigated to be able to understand the generation mechanism and identify their sources. The approach is to use the hybrid computational aeroacoustics  (CAA) method, that couples a computational fluid dynamics (CFD) method with the Ffowcs Williams and Hawkings (FW-H) acoustic analogy. Recirculating flows, which are responsible for reducing the fan efficiency and increasing the noise generation, are observed between the shroud and the blade trailing edges. It is found that the recirculating flows are associated with the gap between the shroud and the inlet duct. The recirculating flow causes large modeled turbulence kinetic energy (TKE). The TKE is unevenly distributed among the blades due to the unsteady recirculating flow. Moreover, the position of the largest TKE periodically varies among the blades. The period corresponds to approximately 4 times the fan rotation period, it was also found in acoustic measurements. Different pressure distributions among the blades are found and ascribed to the turbulence initializing from the inlet gap. The turbulence develops along the shroud wall and interacts with the blades at their leading edges. The interaction renders uneven surface pressure distributions among the blades as well as significant peak differences. As the distances to the inlet gap and the shroud increases, the difference of the pressure distributions among the blades decays. The wall-pressure fluctuations indicates that the locations of the tonal noise sources agree with the locations of the uneven surface pressure distributions and the significant pressure peaks, which are near the blade leading edges.
  •  
34.
  • Rao, Anirudh Narayan, 1985, et al. (author)
  • Influence of the numerical schemes on the flow states of a simplified heavy vehicle
  • 2018
  • In: Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer. - 2377-2816. ; 2018-July, s. 731-734
  • Conference paper (peer-reviewed)abstract
    • Recent experiments [1, 2] in the wake of a simplified heavy vehicle (also know as a ground transportation system (GTS)) have shown that the flow topology remains invariant over a large range of Reynolds numbers [3.8 × 10 4 − 2.8 × 10 6 ]. This allows numerical techniques such as large eddy simulations (LES) to accurately predict the flow topology at low Reynolds numbers. While LES requires grids of higher spatial resolution; hybrid RANS/LES turbulence models are an alternate choice, where, accurate prediction of the flow is possible on coarser grids ([3, 4]). Numerical simulations are performed using LES and a hybrid turbulence model - partially-averaged Navier–Stokes (PANS) equations at Re H = 3.8 × 10 4 for a unified tractor-trailer geometry to compare the flow topologies in the near wake. The influence of the numerical schemes on the flow topology in the symmetry plane which is susceptible to bi-stable flow is investigated using PANS, and compared with the results from LES.
  •  
35.
  • Sarmast, Sasan, et al. (author)
  • Validation of the actuator line and disc techniques using the New Mexico measurements
  • 2016
  • In: Journal of Physics, Conference Series. - : Institute of Physics (IOP). - 1742-6588 .- 1742-6596. ; 753:3
  • Journal article (peer-reviewed)abstract
    • Actuator line and disc techniques are employed to analyse the wake obtained in the New Mexico wind turbine experiment. The New Mexico measurement campaign done in 2014 is a follow-up to the MEXICO campaign, which was completed in 2006. Three flow configurations in axial flow condition are simulated and both computed loads and velocity fields around the rotor are compared with detailed PIV measurements. The comparisons show that the computed loadings are generally in agreement with the measurements under the rotor's design condition. Both actuator approaches under-predicted the loading in the inboard part of blade in stall condition as only 2D airfoil data were used in the simulations. The predicted wake velocities generally agree well with the PIV measurements. In the experiment, PIV measurements are also provided close to the hub and nacelle. To study the effect of hub and nacelle, numerical simulations are performed both in the presence and absence of the hub geometry. This study shows that the large hub used in the experiment has only small effects on overall wake behaviour.
  •  
36.
  • Wang, Chenglong, et al. (author)
  • An Experimental Study of Heat Transfer on an Outlet Guide Vane
  • 2014
  • In: ASME Turbo Expo 2014: Turbine Technical Conference and Exposition, GT 2014; Dusseldorf; Germany; 16 June 2014 through 20 June 2014. - 9780791845721 ; 5B, s. UNSP V05BT14A001-, s. 001-14
  • Conference paper (peer-reviewed)abstract
    • In the present study, the heat transfer characteristics on the suction and pressure sides of an outlet guide vane (OGV) are investigated by using liquid crystal thermography (LCT) method in a linear cascade. Because the OGV has a complex curved surface, it is necessary to calibrate the LCT by taking into account the effect of viewing angles of the camera. Based on the calibration results, heat transfer measurements of the OGV were conducted. Both on- and off-design conditions were tested, where the incidence angles of the OGV were 25 degrees and -25 degrees, respectively. The Reynolds numbers, based on the axial flow velocity and the chord length, were 300,000 and 450,000. In addition, heat transfer on suction side of the OGV with +40 degrees incidence angle was measured. The results indicate that the Reynolds number and incidence angle have considerable influences upon the heat transfer on both pressure and suction surfaces. For on-design conditions, laminarturbulent boundary layer transitions are on both sides, but no flow separation occurs; on the contrary, for off-design conditions, the position of laminar-turbulent boundary layer transition is significantly displaced downstream on the suction surface, and a separation occurs from the leading edge on the pressure surface. As expected, larger Reynolds number gives higher heat transfer coefficients on both sides of the OGV.
  •  
37.
  •  
38.
  • Yarmohamadi, Hoda, 1980, et al. (author)
  • Modeling of elastomeric engine mounts for commercial vehicles
  • 2007
  • In: Proceedings of the 20th Nordic Seminar on Computational Mechanics, NSCM 20, R.Larsson and K. Runesson (eds.), 23-24 November, 2007, Göteborg, Sweden. - 1652-8549.
  • Conference paper (other academic/artistic)abstract
    • In this paper, a model of the conventional engine mount is developed and the nonlinear behavior of dynamic stiffness and damping of the engine mounts of commercial vehicles are investigated. The model comprises elastic, viscous and friction functional components and expresses the stiffness and damping of the mount as a function of frequency and amplitude of harmonic excitation. Optimization is done to identify model parameters using measurements for real elastomeric engine mounts.
  •  
39.
  • Khodadad, Davood, et al. (author)
  • Full-field 3D deformation measurement : Comparison between speckle phase and displacement evaluation
  • 2016
  • In: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165 .- 0003-6935 .- 1539-4522. ; 55:27, s. 7735-7743
  • Journal article (peer-reviewed)abstract
    • The objective of this paper is to describe a full-field deformation measurement method based on 3D speckle displacements. The deformation is evaluated from the slope of the speckle displacement function that connects the different reconstruction planes. For our experiment, a symmetrical arrangement with four illuminations parallel to the planes (x,z) and (y,z) was used. Four sets of speckle patterns were sequentially recorded by illuminating an object from the four directions, respectively. A single camera is used to record the holograms before and after deformations. Digital speckle photography is then used to calculate relative speckle displacements in each direction between two numerically propagated planes. The 3D speckle displacements vector is calculated as a combination of the speckle displacements from the holograms recorded in each illumination direction. Using the speckle displacements, problems associated with rigid body movements and phase wrapping are avoided. In our experiment, the procedure is shown to give the theoretical accuracy of 0.17 pixels yielding the accuracy of 2 × 10-3 in the measurement of deformation gradients
  •  
40.
  • Simmons, Gregory F, et al. (author)
  • Steady state and dynamic characteristics for guide bearings of a hydro-electric unit
  • 2014
  • In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology. - : SAGE Publications. - 1350-6501 .- 2041-305X. ; 228:8, s. 836-848
  • Journal article (peer-reviewed)abstract
    • Experiments are conducted using a 10-MW Kaplan hydropower machine which is outfitted with an extensive array of sensors to determine oil film thickness, pad load and oil temperature in all three guide bearings as well as motion of the shaft in relation to both the bearing housings and the concrete foundation. Test results for all journal bearings are compared to a commercial rotor dynamics model and results for the central journal bearing are compared to a multi-physics model to provide insight into the machine's steady state and dynamic characteristics and their variations during normal operation.
  •  
41.
  • Soltani Dehkharqani, Arash, et al. (author)
  • Fluid added polar inertia and damping for the torsional vibration of a Kaplan turbine model runner considering multiple perturbations
  • 2019
  • In: IOP Conference Series. - : Institute of Physics (IOP).
  • Conference paper (peer-reviewed)abstract
    • A water turbine runner is exposed to several perturbation sources with differentfrequencies, phases, and amplitudes both at the design and off-design operations. Rotor-statorinteraction, cavitation, rotating vortex rope, and blade trailing edge vortices are examples of suchperturbations which can disturb the runner. The rotor dynamic coefficients require beingdetermined to perform a reliable dynamic analysis. Fluid added inertia, damping, and stiffnesshave previously been investigated for individual perturbation frequencies for the torsionalvibration of a Kaplan turbine model runner. However, a number of perturbation sources mostlytake place simultaneously and alter the dynamics of the runner. Soltani et al. [1] have evaluatedthe torsional added parameters for a Kaplan turbine runner using numerical simulationsconsidering single perturbation frequency. In the present work, the fluid added parameters areassessed in the presence of multiple perturbation sources. A similar methodology is used. Asingle-degree-of-freedom (SDOF) model for the dynamic model and unsteady ReynoldsaveragedNavier–Stokes approach for the flow simulations are assumed. Perturbations withdifferent frequencies are applied to the rotational speed of the runner to determine the fluid addedparameters for the torsional vibration. A number of previously investigated frequencies arechosen and their combinations are investigated. In addition, two different phase shifts areconsidered between the applied perturbations to study the effect of phase. Two more test caseswith higher perturbation amplitude are also conducted to investigate its influence on the fluidadded inertia and damping. The results are compared with the previous study and the interactionof multiple perturbations on the added parameters is investigated.
  •  
42.
  • Yu, Rixin, et al. (author)
  • Effect of Turbulence on HCCI Combustion
  • 2007
  • In: Session: Homogeneous Charge Compression Ignition (HCCI) (Part 4 of 8) Combustion Modeling / Optical Diagnostics. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
  • Conference paper (peer-reviewed)abstract
    • This paper presents large eddy simulation (LES) and experimental studies of the combustion process of ethanol/air mixture in an experimental optical HCCI engine. The fuel is injected to the intake port manifolds to generate uniform fuel/air mixture in the cylinder. Two different piston shapes, one with a flat disc and one with a square bowl, were employed to generate different in-cylinder turbulence and temperature field prior to auto-ignition. The aim of this study was to scrutinize the effect of in-cylinder turbulence on the temperature field and on the combustion process. The fuel tracer, acetone, is measured using laser induced fluorescence (LIF) to characterize the reaction fronts, and chemiluminescence images were recorded using a high speed camera, with a 0.25 crank angle degree resolution, to further illustrate the combustion process. Pressure in the cylinder is recorded in the experiments. Spatial and temporal resolved LES was used to gain information on the turbulence mixing, heat transfer and combustion process. It was shown that gas temperature in the piston bowl is generally higher than that in the squish, leading to an earlier ignition in the bowl. Compared to the disc engine, the square bowl engine has a higher temperature inhomogeneity owing to the turbulence wall heat transfer. The experimentally observed higher combustion duration and slower pressure rise rate in the square bowl engine as compared to the disc engine can be explained by the higher temperature inhomogeneity in the square bowl engine.
  •  
43.
  • Karlsson, Stefan, 1984-, et al. (author)
  • Non-destructive strength testing of microindented float glass by a nonlinear acoustic method
  • 2023
  • In: Construction and Building Materials. - 0950-0618 .- 1879-0526. ; 391
  • Journal article (peer-reviewed)abstract
    • The present paper describes a method for non-destructive testing of the glass strength. Square 10 × 10 cm2 samples of annealed float glass was inflicted with a controlled defect in the centre of the atmospheric side using Vickers microindentation-induced cracking with a force of 2 N, 5 N and 10 N and compared to an un-indented reference. The samples were non-destructively tested using a nonlinear acoustic wave method resulting in defect values. The average of the defect values was found to linearly correlate to the indentation force in a log–log relationship. The samples were subsequently tested in a ring-on-ring setup that allows for an equibiaxial stress state. The indentation-induced cracking gave practically realistic strength values in the range of 45 to 110 MPa. The individual sample values for failure stress as a function of normalized defect value show linear trends with approximately half of the data within 95% confidence limit. In summary, this study provides an initial proof-of-concept for a non-destructive testing of the strength of glass.
  •  
44.
  • Aghaali, Habib, 1981-, et al. (author)
  • Demonstration of Air-Fuel Ratio Role in One-Stage Turbocompound Diesel Engines
  • 2013
  • In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
  • Conference paper (peer-reviewed)abstract
    • A large portion of fuel energy is wasted through the exhaust of internal combustion engines. Turbocompound can, however, recover part of this wasted heat. The energy recovery depends on the turbine efficiency and mass flow as well as the exhaust gas state and properties such as pressure, temperature and specific heat capacity.The main parameter influencing the turbocompound energy recovery is the exhaust gas pressure which leads to higher pumping loss of the engine and consequently lower engine crankshaft power. Each air-fuel equivalence ratio (λ) gives different engine power, exhaust gas temperature and pressure. Decreasing λ toward 1 in a Diesel engine results in higher exhaust gas temperatures of the engine.  λ can be varied by changing the intake air pressure or the amount of injected fuel which changes the available energy into the turbine. Thus, there is a compromise between gross engine power, created pumping power, recovered turbocompound power and consumed compressor power.In this study, the effects of different λ values and exhaust back-pressure have been investigated on the efficiency of a heavy-duty Diesel engine equipped with a single-stage electric turbocompounding. A one-dimensional gas dynamics model of a turbocharged engine was utilized that was validated against measurements at different load points. Two configurations of turbocompound engine were made. In one configuration an electric turbocharger was used and the amount of fuel was varied with constant intake air pressure. In another configuration the turbocharger turbine and compressor were disconnected to be able to control the turbine speed and the compressor speed independently; then the compressor pressure ratio was varied with constant engine fuelling and the exhaust back-pressure was optimized for each compressor pressure ratio.At each constant turbine efficiency there is a linear relation between the optimum exhaust back-pressure and ideally expanded cylinder pressure until bottom dead center with closed exhaust valves. There is an optimum λ for the turbocharged engine with regard to the fuel consumption. In the turbocompound engine, this will be moved to a richer λ that gives the best total specific fuel consumption; however, the results of this study indicates that turbocompound engine efficiency is relatively insensitive to the air-fuel ratio.
  •  
45.
  • Aghaali, Habib, 1981-, et al. (author)
  • Temperature Estimation of Turbocharger Working Fluids and Walls under Different Engine Loads and Heat Transfer Conditions
  • 2013
  • In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
  • Conference paper (peer-reviewed)abstract
    • Turbocharger performance maps, which are used in engine simulations, are usually measured on a gas-stand where the temperatures distributions on the turbocharger walls are entirely different from that under real engine operation. This should be taken into account in the simulation of a turbocharged engine. Dissimilar wall temperatures of turbochargers give different air temperature after the compressor and different exhaust gas temperature after the turbine at a same load point. The efficiencies are consequently affected. This can lead to deviations between the simulated and measured outlet temperatures of the turbocharger turbine and compressor. This deviation is larger during a transient load step because the temperatures of turbocharger walls change slowly due to the thermal inertia. Therefore, it is important to predict the temperatures of turbocharger walls and the outlet temperatures of the turbocharger working fluids in a turbocharged engine simulation.In the work described in this paper, a water-oil-cooled turbocharger was extensively instrumented with several thermocouples on reachable walls. The turbocharger was installed on a 2-liter gasoline engine that was run under different loads and different heat transfer conditions on the turbocharger by using insulators, an extra cooling fan, radiation shields and water-cooling settings. The turbine inlet temperature varied between 550 and 850 °C at different engine loads.The results of this study show that the temperatures of turbocharger walls are predictable from the experiment. They are dependent on the load point and the heat transfer condition of the turbocharger. The heat transfer condition of an on-engine turbocharger could be defined by the turbine inlet temperature, ambient temperature, oil heat flux, water heat flux and the velocity of the air around the turbocharger. Thus, defining the heat transfer condition and rotational speed of the turbocharger provides temperatures predictions of the turbocharger walls and the working fluids. This prediction enables increased precision in engine simulation for future work in transient operation.
  •  
46.
  • Avellan, Rickard, 1976, et al. (author)
  • Preparing for Proof-of-concept of a Novel Propeller for Open Rotor Engines
  • 2015
  • In: ISABE-2015-20097.
  • Conference paper (peer-reviewed)abstract
    • This article describes the development of a novel high-speed propeller concept. Large-scale propeller tests are extremely expensive and thus not appropriate at early R&D development phases. A convenient approach is to use computational methods validated by small-scale tests with propellers manufactured from low-cost materials and rapid manufacturing methods. The present paper is describing this cross validation work explaining differences between numerics and experiments. Preferred materials and manufacturing methods for high-speed future wind tunnel tests are discussed. We also discuss the progress of development of the aerodynamic design of the concept propeller.
  •  
47.
  • Ferreira da Silva, Janaina, et al. (author)
  • Considering the Effects of Turbine Blade Cooling on Engine Performance Estimation
  • 2017
  • In: Proceedings of the 23rd ISABE conference 2017.
  • Conference paper (peer-reviewed)abstract
    • In gas turbines, a way to improve the engine performance is by increasing the Turbine Inlet Temperature (TIT). However, increasing TIT causes an increase in heat load of turbine components. A limit in the performance improvement is imposed by the permissible metal temperature. Engine running above the melting point of material might be achieved only by cooling turbine components or using Thermal Barrier Coating (TBC). This thermal management must be done to ensure safe and durable engine operation. The most common method to cool turbine components is bleed a portion of the compressor airflow and inject it on blades and disks. Unfortunately, the extraction has an adverse effect on engine performance compared with engine without bleed. In this paper, the cooling effects on engine performance estimation at preliminary design was analyzed. The engine configuration used in the study is a turboshaft – single spool gas turbine engine. The coolant parameters are estimated using the method developed by Young and Wilcock. The results showed that there is a marked difference on performance for uncooled and cooled turbine blades, highlighting the importance in considering the cooling on performance estimation since design preliminary phase. Ignoring the cooling in evaluation can cause up to 15% difference in net specific work.
  •  
48.
  • Grönstedt, Tomas, 1970, et al. (author)
  • Ultra low emission technology innovations for mid-century aircraft turbine engines
  • 2016
  • In: ASME Turbo EXPO 2016, Seoul, June 13-17, South Korea. - 9780791849743 ; 3:GT2016-56123
  • Conference paper (peer-reviewed)abstract
    • Commercial transport fuel efficiency has improved dramatically since the early 1950s. In the coming decades the ubiquitous turbofan powered tube and wing aircraft configuration will be challenged by diminishing returns on investment with regards to fuel efficiency. From the engine perspective two routes to radically improved fuel efficiency are being explored; ultra-efficient low pressure systems and ultra-efficient core concepts. The first route is characterized by the development of geared and open rotor engine architectures but also configurations where potential synergies between engine and aircraft installations are exploited. For the second route, disruptive technologies such as intercooling, intercooling and recuperation, constant volume combustion as well as novel high temperature materials for ultra-high pressure ratio engines are being considered. This paper describes a recently launched European research effort to explore and develop synergistic combinations of radical technologies to TRL 2. The combinations are integrated into optimized engine concepts promising to deliver ultra-low emission engines. The paper discusses a structured technique to combine disruptive technologies and proposes a simple means to quantitatively screen engine concepts at an early stage of analysis. An evaluation platform for multidisciplinary optimization and scenario evaluation of radical engine concepts is outlined.
  •  
49.
  • Gullberg, Peter, 1983, et al. (author)
  • Axial fan performance predictions in CFD, comparison of MRF and sliding mesh with experiments
  • 2011
  • In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International. - 0148-7191 .- 2688-3627. ; 2011
  • Journal article (peer-reviewed)abstract
    • Underhood Thermal Management has become an important topic for the majority of automotive OEM's. To keep combustion engines cool and manage waste heat efficiently is an important part in the design of vehicles with low fuel consumption. To be able to predict cooling performance and underhood airflow with good precision within a virtual design process, it is of utmost importance to model and simulate the cooling fan efficiently and accurately, and this has turned out to be challenging. Simulating the cooling fan in a vehicle installation involves capturing complex fluid dynamic interaction between rotating blades and stationary objects in the vicinity of the fan. This interaction is a function of fan rotation rate, fan blade profile, upstream and downstream installation components. The flow is usually highly turbulent and small geometry details, like the distance between the blade tip and the fan shroud, have strong impact on the fan performance characteristics. Fan installations therefore have a large influence on cooling performance which the fan data from the supplier cannot capture. Improved simulation capabilities in this area are critical for optimizing the design of energy efficient vehicles since the performance of these fans, which provide airflow to the heat exchangers used for engine cooling and HVAC system operation, have a big impact on the vehicles' overall energy efficiency. This paper presents a comparison of two methodologies for simulating fan air flows. Multiple Reference Frame (MRF) and Sliding Mesh (SM) techniques are applied for a typical heavy duty truck fan. Simulation results are compared to experimental data obtained in a fan test rig with representation of a typical truck fan installation, including fan shroud, ring, seal and an engine silhouette downstream. Results of MRF simulations are known to be sensitive to the MRF domain, which is highly constrained in tight fan installations. For typical truck installations, SM provides a more robust alternative, and better accuracy than MRF in the transitional and radial regime of the fan curve.
  •  
50.
  • Kyprianidis, Konstantinos, et al. (author)
  • Dynamic performance investigations of a turbojet engine using a cross-application visual oriented platform
  • 2008
  • In: Aeronautical Journal. - 0001-9240. ; 112:1129, s. 161-169
  • Journal article (peer-reviewed)abstract
    • This paper presents the development of visual oriented tools for the dynamic performance simulation of a turbojet engine using a cross-application approach. In particular, the study focuses on the feasibility of developing simulation models using different programming environments and linking them together using a popular spreadsheet program. As a result of this effort, a low fidelity cycle program has been created, capable of being integrated with other performance models. The amount of laboratory sessions required for student training during an educational procedure, for example for a course in gas turbine performance simulation, is greatly reduced due to the familiarity of most students with the spreadsheet software. The model results have been validated using commercially available gas turbine simulation software and experimental data from open literature. The most important finding of this study is the capability of the program to link to aircraft performance models and predict the transient working line of the engine for various initial conditions in order to dynamically simulate flight phases including take-off and landing.
  •  
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