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research-article  
Hailin Li, Timothy Gatts, Shiyu Liu, Scott Wayne, Nigel N. Clark and Daniel Mather
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038692
This research investigated the combustion process of an AVL Model LEF/Volvo 5312 single cylinder engine configured to simulate the operation of heavy-duty spark ignition (SI) natural gas engine operated on stoichiometric mixture. The factors affecting the combustion process examined include intake pressure, spark timing, and the addition of diluents including N2 and CO2 to natural gas simulating low BTU gases. The mixing of diluents with natural gas is able to slow down the flame propagation speed, suppress the onset of knock, and allow the engine to operate on higher boost pressure for higher power output. The addition of CO2 was more effective than N2 in suppressing the onset of knock and the propagation speed due to its high heat capacity and diluting impact. Boosting intake pressure significantly increased the heat release rate. However, its impact on the normalized heat release ratio was relatively minor. The significant impact of intake pressure on heat release rate was due to the increased mass of fuel burned. The combustion process of a boosted engine can be approximated by examining the heat release rate measured under a naturally aspirated condition. This makes it convenient for researchers to numerically simulate the combustion process and the onset of knock of turbocharged SI natural gas engines under development using combustion process data measured under naturally aspirated condition as a reference.
TOPICS: Combustion, Gas engines, Pressure, Heat, Natural gas, Carbon dioxide, Engines, Diluents, Single-cylinder engines, Heat capacity, Flames, Ignition, Gases, Fuels
research-article  
Gen Fu, Alexandrina Untaroiu and Erik E. Swanson
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038693
Gas foil bearing can operate in extreme conditions such as high temperature and high rotating speed, compared to traditional bearings. They also provide better damping and stability characteristics and have larger tolerance to debris and rotor misalignment. In the previous decades, a lot of theoretical and experimental work have been conducted to investigate the properties of gas foil bearings. However, very little work has been done to study the influence of the foil bearing pad geometry configuration using CFD. This study proposes a robust approach to analyze the effect of the foil geometry on the performance of a six pads thrust foil bearing. A 3D CFD model for a parallel six-pads thrust foil bearing is created. In order to predict the thermal property, the total energy with viscous dissipation is used. The geometry of the thrust foil bearing is parameterized and analyzed using DOE methodology. The selected geometry parameters of the foil structure include: minimum film thickness, inlet film thickness, the ramp extent on the inner circle, the ramp extent on the outer circle, the arc extent of the pad, and the orientation of the leading edge. The objectives in the sensitivity study are load force and maximal temperature. An optimal foil geometry is derived based on the results of the DOE process by using a goal driven optimization technique to maximize the load force and minimize the maximal temperature. The results show that the geometry of foil structure is a key factor for foil bearing performance.
TOPICS: Thrust, Geometry, Foil bearings, Film thickness, Temperature, Stress, Computational fluid dynamics, Damping, Optimization, Rotors, Energy dissipation, Thermal properties, Bearings, Stability, High temperature
Errata  
Joel Harris and Dara Childs
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038615
The following erratum has been written to alert readers to unreliable data contained in the referenced paper.
TOPICS: Journal bearings, Performance characterization
Discussion  
Kyriakos Kourousis
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038616
N/A
TOPICS: Creep, Gas turbines, oxidation, Thermal barrier coatings
research-article  
Jason C. Wilkes, Jonathan Wade, Aaron Rimpel, J. Jeffrey Moore, Erik E. Swanson, Joseph Grieco and Jerry Brady
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038603
High speed foil bearings are currently used in increasingly demanding, high performance applications. The application under consideration is a 120 krpm natural gas turboexpander-compressor, which requires 38 mm (1.5 in.) foil journal bearings with high stiffness and load capacity to help enhance rotordynamic stability. This paper describes the development of the foil bearing for this application and includes measured stiffness and damping coefficients recorded on a high-speed dynamic bearing test rig. The dynamic test data were taken for several different foil bearing configurations with varying spring-element foil thicknesses, number of spring-element foils, and bearing shim thickness. All three parameters have a direct impact on bearing clearance. The influence of these different parameters on measured stiffness and damping coefficients and thermal performance of the bearings are presented and discussed.
TOPICS: Clearances (Engineering), Bearings, Damping, Stiffness, Journal bearings, Foil bearings, Springs, Stability, Compressors, Stress, Natural gas
research-article  
Mustapha Chaker
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038604
Gas Turbine output is strongly dependent of the ambient air temperature. This decrease is usually occurs in the hot afternoon during the peak demand for power. One way to counter this drop in output is to cool the inlet air using one of the available cooling technologies such as the inlet fog cooling of gas turbine engines for power augmentation. This technology is well-established with over 1,000 fogging systems installed all around the world on gas turbines of various makes and sizes ranging from 5MW to 250MW. Two droplet diameters are used to characterize the droplet sizes from nozzles used in the fogging systems, namely D32 (Sauter mean diameter) and Dv90 (diameter for which 90% of the water volume in the spray is less than or equal to). This paper will show the importance of each diameter on the performance of fogging systems. For this purpose, a heat and mass transfer theoretical model is developed to analyze the dynamics of evaporation of fog droplets. The model will quantify the evaporative efficiency of fog droplets for different D32 and Dv90 values derived from experimentally measured droplet size distributions at two typical ambient psychrometric conditions: hot and dry, and cold and Humid
TOPICS: Evaporation, Gas turbines, Sensitivity analysis, Drops, Cooling, Water, Nozzles, Sprays, Dynamics (Mechanics), Heat, Temperature, Mass transfer
research-article  
Martina Hohloch, Andreas Huber and Manfred Aigner
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038605
The present work deals with the analysis of operational concepts for a SOFC/MGT hybrid power plant based on a test rig at the DLR, Institute of Combustion Technology. Here, a Turbec T100 micro gas turbine and a fuel cell emulator are used. The emulator is composed of two pressure vessels. The first represents the cathode volume of the fuel cell to simulate the residence time and pressure loss. The second is equipped with a natural gas combustor to emulate the varying heat input of the fuel cell. The MGT and the SOFC are connected via different piping paths. The procedures start-up, load change and shutdown are analyzed in matters of temperature gradients, pressure gradients and fluctuations, as well as the air mass flow provided at the interconnections to the coupling elements. To achieve the required inlet conditions of the SOFC, transient operations, using the different piping paths, are investigated. Concepts for heating-up and cooling the SOFC using hot air from the recuperator and relatively cold air from the compressor outlet are experimentally tested and characterized. Selected critical situations and their effect on the SOFC are investigated. An emergency operation, its impact on both subsystems and limitations are shown. Further operational limits of the MGT control system and power electronic were observed and analyzed. Based on the experimental results, the applicability of the used MGT procedures in a hybrid power plant was reconsidered. Finally, adaptions and strategies for the operational concept are derived and discussed.
TOPICS: Solid oxide fuel cells, Hybrid power systems, Fuel cells, Pipes, Natural gas, Pressure gradient, Heating, Micro gas turbines, Combustion technologies, Emergencies, Temperature gradient, Pressure, Flow (Dynamics), Heat, Cooling, Control systems, Compressors, Pressure vessels, Stress, Fluctuations (Physics), Transients (Dynamics), Combustion chambers
research-article  
Masahiro Negami, Shinya Hibino, Akihito Kawano, Yoshimichi Nomura, Ryozo Tanaka and Kenichiroh Igashira
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038607
Durability of thermal barrier coating (TBC) systems is important because of recent rising of TIT (Turbine inlet temperature) for improved efficiency of industrial gas turbine engines. For improving durability of TBC, we focused on thermal pre-oxidation methods as a means for forming an alpha-Al2O3 barrier layer on the bond coat. The alpha-Al2O3 barrier layer is effective in reducing the growth rate of thermally grown oxide (TGO). We studied the suitable pre-oxidation conditions for forming barrier layer. In this study, we analyzed the oxidation behavior of the bond coat surface during pre-oxidation heat treatment by means of in-situ synchrotron X-ray diffraction (XRD) analysis. As a result, if the thermal treatment is conducted under some specific low oxygen partial pressure condition, only alpha-Al2O3 is formed without formation of metastable alumina. TEM analysis of oxide scale formed after pre-oxidation heat treatment revealed that a monolithic alpha-Al2O3 layer is formed on the bond coat if pre-oxidation is performed under specific oxygen partial pressure conditions. We performed a durability evaluation test of TBC with the monolithic alpha-Al2O3 layer formed by pre-oxidation of the bond coat. An isothermal oxidation test confirmed that the growth of TGO in the TBC that had undergone pre-oxidation was more favorably suppressed than that in the TBC without pre-oxidation.
TOPICS: Thermal barrier coatings, oxidation, Durability, Oxygen, Pressure, Heat treating (Metalworking), Temperature, X-ray diffraction, Industrial gases, Gas turbines, Turbines
research-article  
Nicola Aldi, Nicola Casari, Devid Dainese, Mirko Morini, Michele Pinelli, Pier Ruggero Spina and Alessio Suman
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038608
Solid particle ingestion is one of the principal degradation mechanisms in the compressor and turbine sections of gas turbines. This paper presents numerical simulations of the micro-particle ingestion in a multistage subsonic axial compressor, carried out by means of a commercial computational fluid dynamic code. Particle trajectory simulations use a stochastic Lagrangian tracking method that solves the equations of motion separately from the continuous phase. The adopted computational strategy allows the evaluation of particle deposition in a multistage compressor thanks to the use of a mixing plane approach to model the rotor/stator interaction. The compressor numerical model and the discrete phase model are set up and validated against the experimental and numerical data available in literature. The number of particles and sizes are specified in order to perform a quantitative analysis of the particle impacts on the blade surface. The blade zones affected by particle impacts and the kinematic characteristics of the impact of micrometric and sub-micrometric particles with the blade surface are shown. The particle deposition is established by using the sticking probability, which links the kinematic characteristics of particle impact on the blade with the fouling phenomenon. The results show that micro-particles tend to follow the flow by impacting on the compressor blades at full span. The suction side of the blade is only affected by the impacts of the smallest particles. Particular fluid dynamic phenomena strongly influence the impact location of the particles. The impact and deposition trends decrease according to the stages.
TOPICS: Particulate matter, Compressors, Computational fluid dynamics, Blades, Particle collisions, Kinematics, Computer simulation, Microparticles, Probability, Stators, Engineering simulation, Gas turbines, Rotors, Turbines, Flow (Dynamics), Fluids, Suction, Equations of motion, Trajectories (Physics), Simulation
research-article  
Paul Jourdaine, Clement Mirat, Jean Caudal and Thierry Schuller
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038617
The stabilization of premixed flames within a swirling flow produced by an axial-plus-tangential swirler is investigated. In this system, flames are stabilized aerodynamically away from the solid elements of the combustor without help of any solid anchoring device. Experiments are reported for lean CH4/air mixtures, eventually also diluted with N2, with injection Reynolds numbers varying from 8 500 to 25 000. Changes of the flame shape are examined with OH* chemiluminescence and OH-LIF measurements as a function of the operating conditions. PIV measurements are used to reveal the structure of the velocity field in nonreacting and reacting conditions. It is shown that the axial-plus-tangential swirler allows to easily control the flame shape and the position of the flame leading edge. The ratio of the bulk injection velocity over the laminar burning velocity, the adiabatic flame temperature and the swirl number are shown to control the flame shape and its position. It is then shown that the axial velocity field produced by the axial-plus-tangential swirler is different from those produced by purely axial or radial devices. It takes here a W-shape profile with three local maxima and two minima. The mean turbulent flame front also takes this W-shape, with two lower positions located slightly off-axis and corresponding to the positions where the axial flow velocity is the lowest. It is finally shown that these positions can be inferred from axial flow velocity profiles under non-reacting conditions.
TOPICS: Flames, Swirling flow, Shapes, Axial flow, Methane, Temperature, Combustion, Turbulence, Reynolds number, Chemiluminescence, Combustion chambers
research-article  
Eric Kurstak and Kiran X. D'Souza
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038613
Current efforts to model multistage turbomachinery systems rely on calculating independent constraint modes for each degree of freedom on the boundary between stages. While this approach works, it is computationally expensive to calculate all the required constraint modes. This paper presents a new way to calculate a reduced set of constraint modes referred to as Fourier constraint modes (FCMs). These FCMs greatly reduce the number of computations required to construct a multistage reduced order model (ROM). The FCM method can also be integrated readily with the component mode mistuning method to handle small mistuning and the pristine rogue interface modal expansion method to handle large and/or geometric mistuning. These methods all use sector level models and calculations, which makes them very efficient. This paper demonstrates the efficiency of the FCM method on a multistage system that is tuned and, for the first time, creates a multistage ROM with large mistuning using only sector level quantities and calculations. The results of the multistage ROM for the tuned and large mistuning cases are compared with full finite element results and are found in good agreement.
TOPICS: Degrees of freedom, Finite element analysis, Modeling, Computation, Turbomachinery
research-article  
Riccardo Da Soghe, Cosimo Bianchini and Jacopo D'Errico
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038618
This paper deals with a numerical study aimed at the validation of a computational procedure for the aerothermal characterization of pre-swirl systems employed in axial gas turbines. The numerical campaign focused on an experimental facility which models the flow field inside a direct-flow pre-swirl system. Steady and unsteady simulation techniques were adopted in conjunction with both a standard two-equations RANS/URANS modelling and more advanced approaches such as the Scale-Adaptive-Simulation principle, the SBES and LES. Overall the steady-state CFD predictions are in reasonable good agreement with the experimental evidences even though they are not able to confidently mimic the experimental swirl and pressure behaviour in some regions. Scale resolved approaches improve the computations accuracy significantly especially in terms of static pressure distribution and heat transfer on the rotating disc. Although the use of direct turbulence modelling, would in principle increase the insight in the physical phenomenon, from a design perspective the trade-off between accuracy and computational costs is not always favourable.
TOPICS: Flow (Dynamics), Heat transfer, Pressure, Simulation, Modeling, Computation, Reynolds-averaged Navier–Stokes equations, Rotating Disks, Steady state, Tradeoffs, Computational fluid dynamics, Design, Gas turbines, Turbulence
research-article  
Hongmei Jiang, Li He, Qiang Zhang and Lipo Wang
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038619
Modern High Pressure Turbine (HPT) blades operate at high speed conditions. The Over-Tip-Leakage (OTL) flow can be high-subsonic or even transonic. From the consideration of problem simplification and cost reduction, the OTL flow has been studied extensively in low speed experiments. It has been assumed a redesigned low speed blade profile with a matched blade loading should be sufficient to scale the high speed OTL flow down to the low speed condition. In this paper, the validity of this conventional scaling approach is computationally examined. The CFD methodology was firstly validated by experimental data conducted in both high and low speed conditions. Detailed analyses on the OTL flows at high and low speed conditions indicate that, only matching the loading distribution with a redesigned blade cannot ensure the match of the aerodynamic performance at the low speed condition with that at the high-speed condition. Specifically, the discrepancy in the peak tip leakage mass flux can be as high as 22.2%, and the total pressure loss at the low speed condition is 10.7% higher than the high speed case. An improved scaling method is proposed hereof. As an additional dimension variable, the tip clearance can also be "scaled" down from the high speed to low speed case to match the cross-tip pressure gradient between pressure and suction surfaces. The similarity in terms of the overall aerodynamic loss and local leakage flow distribution can be improved by adjusting the tip clearance, either uniformly or locally.
TOPICS: Flow (Dynamics), Leakage, Blades, Clearances (Engineering), Pressure, Computational fluid dynamics, Turbines, Pressure gradient, Leakage flows, Suction, Dimensions, High pressure (Physics)
research-article  
Qu Meijiao and Chen Guo
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038542
A finite element model of an aero engine rotor tester, which thin-wall casing structure and actual engine mounting, is established to simulate the intrinsic vibration characteristics under actual engine mounting condition. Firstly, the modal experiment of the whole aero-engine rotor tester is conducted, and the finite element simulation model is modified and validated based on the modal experimental results. Secondly, the first 3 orders natural frequencies and modal shapes are calculated by the modified finite element model under three kinds of the different mounting stiffness that are respectively the fixed mounting border, the free mounting border, and the flexible mounting border, and the influence of the mounting stiffness on the rotor and stator coupling vibration is studied by means of a new rotor-stator coupling factor which is proposed in this paper. The results show that, the higher is the rotor-stator coupling degree of the modal shape, the greater influence of the mounting condition on this modal shape is, in additional, the influence of mounting stiffness on the rotor-stator coupling degree is nonlinear. Rotor and stator coupling phenomena exsits in many modal shapes of the actual large turbofan engines, the effect of mounting stiffness on rotor-stator coupling can not be ignored, therefore, the mounting stiffness should be considered carefully in the finite element modeling and simulation for the paractic aero-engine vibration.
TOPICS: Engines, Vibration, Stiffness, Aircraft engines, Rotors, Stators, Shapes, Finite element model, Finite element analysis, Modeling, Simulation, Simulation models, Thin wall structures, Turbofans
research-article  
Leonardo Urbiola-Soto
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038549
Achieving an optimal design of journal bearings is a very challenging effort due the many input and output variables involved, including rotordynamic and tribological responses. This paper demonstrates the use of a multivariate response modeling approach based on Response surface design of experiments to design tilting pad bearings. It is shown that an optimal configuration can be achieved in the early stages of the design process while substantially reducing the amount of calculations. To refine the multivariate response model, statistical significance of the factors was assessed by examining at the test's p-value. The effect coefficient calculation complemented the statistical hypothesis testing as an overall quantitative measure of the strength of factors, namely; main effects, quadratic effects and interactions between variables. This provided insight into the potential non-linearity of the phenomena. Once arriving at an optimized design, a sensitivity analysis was performed to identify the input variables who´s variability have the greatest influence on a given response. Finally, an analysis of percent contribution of each input variable standard deviation to the actual response standard deviation was permormed.
TOPICS: Modeling, Bearings, Sensitivity analysis, Design, Journal bearings, Testing, Experimental design, Response surface methodology, Tribology
research-article  
Kyunghan Min, Haksu Kim, Manbae Han and Myoungho Sunwoo
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038543
Modern diesel engines equip the exhaust gas recirculation (EGR) system because it can suppress NOx emissions effectively. However, since a large amount of exhaust gas might cause the degradation of drivability, the control strategy of EGR system is crucial. The conventional control structure of the EGR system uses the mass air flow (MAF) as a control indicator, and its set-point is determined from the well-calibrated look-up table. However, this control structure cannot guarantee the optimal engine performance during acceleration operating conditions because the MAF set-point is calibrated at steady operating conditions. In order to optimize the engine performance with regards to NOx emission and drivability, an optimization algorithm in a function of the intake oxygen fraction (IOF) is proposed because the IOF directly affects the combustion and engine emissions. Using the NOx and drivability models, the cost function for the performance optimization is designed and the optimal value of the IOF is determined. Then, the MAF set-point is adjusted to trace the optimal IOF under engine acceleration conditions. The proposed algorithm is validated through scheduled engine speeds and loads to simulate the extra-urban driving cycle of the European driving cycle. As validation results, the MAF is controlled to trace the optimal IOF from the optimization method. Consequently, the NOx emission is substantially reduced during acceleration operating conditions without the degradation of drivability.
TOPICS: Diesel engines, Nitrogen oxides, Emissions, Engines, Exhaust gas recirculation, Optimization, Cycles, Combustion, Cities, Air flow, Stress, Algorithms, Exhaust systems, Optimization algorithms, Oxygen
research-article  
Bidesh Sengupta and Chittatosh Bhattacharya
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038544
The steam consumption in a turbine within an operating pressure range determines the effectiveness of thermal energy conversion to electric power generation in a turbo-alternator. The low pressure (LP) stage of the steam turbine produces largest amount of steam to shaft-power in comparison to other stages of turbine although susceptible to various additional losses due to condensation of wet steam near penultimate and ultimate stages. The surface deposition in blade is caused by inertial impaction and turbulent-diffusion. With increasing blade stagger angle along the larger diameter of blading, the fractional deposition of wet steam is largely influenced by blade shape. From this background, the aim of this work is to predict the effect of mathematical models through CFD analysis on the characterization of thermodynamic and mechanical loss components based on unsaturated vapor water droplet size and pressure zones in lowest pressure stages of steam turbine and to investigate the influence of droplet size and rotor blade profile on cumulative energy losses due to condensation and provide an indication about the possible conceptual optimization of blade profile design to minimize moisture induced energy losses.
TOPICS: Drops, Energy dissipation, Blades, Shapes, Steam turbines, Steam, Pressure, Condensation, Turbines, Water, Electric power generation, Vapors, Thermal energy, Turbochargers, Turbulent diffusion, Computational fluid dynamics, Design, Optimization, Rotors
research-article  
Craig Sacco, Christopher Bowen, Ryan Lundgreen, Dr. Jeffrey Bons, Eric Ruggiero, Jason Allen and Jeremy Bailey
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038550
The role of absolute pressure in deposition testing is reviewed from first principles. Relevant dimensionless parameters for deposition testing are developed and dynamic similarity conditions are assessed in detail. Criteria for establishing appropriate conditions for laboratory studies of deposition are established pursuant to the similarity variables. The role of pressure is particularly singled out for consideration relative to other variables such as temperature, particle size, and test article geometry/scaling. A case study is presented for deposition in a generic array of impinging jets. A fixed quantity (2g) of 0-10micron Arizona Road Dust (ARD) is delivered to the impingement array at three different temperatures (290, 500, and 725K) and at fixed pressure ratio. Deposition results are presented for operating pressures from 1 to 15atm. Surface scans show that the height of deposit cones at the impingement sites decreases with increasing pressure at constant temperature and pressure ratio. This reduction is explained by the lower "effective" Stokes number that occurs at high particle Reynolds numbers, yielding fewer particle impacts at high pressure. A companion CFD study identifies the additional role of Reynolds number in both the impingement hole losses as well as the shear layer thickness.
TOPICS: Pressure, Testing, Turbines, Temperature, Reynolds number, Particle collisions, High pressure (Physics), Shear (Mechanics), Jets, Computational fluid dynamics, Particulate matter, Dust, Geometry, Particle size, Roads
research-article  
Ssu-Ying Chien, Mark Cramer, Gen Fu and Alexandrina Untaroiu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038551
Adaptive lubricants involve binary mixture of synthetic oil and dissolved carbon dioxide (CO2). Unlike conventional lubricant oils, the lubricant viscosity not only varies with the temperature within the bearing, but also can be directly adjusted through the CO2 concentration in the system. In this study, we consider the synthetic oil to be fully saturated by CO2 to investigate the maximum impacts of adaptive lubricants on the performance of a hybrid journal bearing. The adaptive lubricant analyzed for this study was the polyalkylene glycol (PAG) oils with low concentration of CO2 (< 30%). A three-dimensional computational ?uid dynamic (CFD) model of the bearing was developed and validated against the experimental data. The mixture composition and the resultant mixture viscosity were calculated as a function of pressure and temperature using empirical equations. The simulation results revealed that the viscosity distribution within the PAG/CO2-lubricated bearing is determined primarily by the pressure at the low operating speed. When the speed becomes higher, it is the temperature effect that dominates the viscosity distribution within the bearing. Moreover, the PAG/CO2-lubricated bearing can reduce up to 12.8% power loss than the PAG-lubricated bearing due to the low viscosity of PAG/CO2 mixture. More importantly, we have found that the PAG/CO2 can enhance the load capacity up to 19.6% when the bearing is operating at the high speed conditions.
TOPICS: Lubricants, Journal bearings, Carbon dioxide, Bearings, Viscosity, Temperature, Pressure, Stress, Lubricating oils, Oils, Petroleum, Simulation results, Computational fluid dynamics
research-article  
Alireza Ameli, Ali Afzalifar, Teemu Turunen-Saaresti and Jari Backman
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038552
Rankine and Brayton cycles are common energy conversion cycles and constitute the basis of a significant proportion of global electricity production. Even a seemingly marginal improvement in the efficiency of these cycles can considerably decrease the annual use of primary energy sources and bring a significant gain in power plant output. Recently, supercritical Brayton cycles using CO2 as the working fluid have attracted much attention, chiefly due to their high efficiency. As with conventional cycles, improving the compressor performance in supercritical cycles is major route to increasing the efficiency of the whole process. This paper numerically investigates the flow field and performance of a supercritical CO2 centrifugal compressor. A thermodynamic look-up table is coupled with the flow solver and the look-up table is systematically refined to take into account the large variation of thermodynamic properties in the vicinity of the critical point. Effects of different boundary and operating conditions are also discussed. It is shown that the compressor performance is highly sensitive to the look-up table resolution as well as the operating and boundary conditions near the critical point. Additionally, a method to overcome the difficulties of simulation close to the critical point is explained.
TOPICS: Compressors, Flow (Dynamics), Supercritical carbon dioxide, Cycles, Brayton cycle, Boundary-value problems, Carbon dioxide, Fluids, Simulation, Resolution (Optics), Energy conversion, Energy resources, Power stations

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