Accepted Manuscripts

Manuel Hildebrandt, Corina Schwitzke and Hans-Jörg Bauer
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038767
Because of the superior sealing characteristics compared to labyrinth seals, brush seals found an increased spread in turbomachinery in recent years. Their outstanding sealing performance results mainly from their flexibility. Thus, a very small gap between the rotor and bristle package can be obtained without running the risk of severe detrimental deterioration in case of rubbing. Thanks to the flexible structure of the brush seal the contact forces during a rubbing event are reduced, however the frictional heat input can still be considerable. The geometry of the seal has a decisive influence on the resulting contact forces and consequently the heat input. The complex interactions between the geometric parameters of the seal and the heat input and leakage characteristics are not yet fully understood. This paper presents the investigation of the influence of the geometric parameters of a brush seal on the heat input into the rotor and the leakage behaviour. Two seals with different packing densities were tested under relevant engine conditions. The transient temperature rise during the rub event was recorded with 24 thermocouples in close proximity to the rub contact embedded in the rotor structure. By comparing the temperature curves with the results of a thermal finite element analysis of the rotor the heat input into the rotor was calculated iteratively. It could be shown that the packing density has a decisive influence on the overall operating behavior of a brush seal. Furthermore, results for the heat flux distribution between seal and rotor are shown.
TOPICS: Heat, Leakage, Rotors, Packing (Shipments), Sealing (Process), Packings (Cushioning), Temperature, Engines, Heat flux, Risk, Density, Transients (Dynamics), Finite element analysis, Flexible structures, Geometry, Thermocouples, Turbomachinery
Chiara Gastaldi, Teresa Berruti and Muzio M. Gola
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038773
The purpose of this paper is to propose an effective strategy for the design of turbine blades with underplatform dampers. The strategy involves damper "pre-optimization", already proposed by the authors, to exclude, before the blades-coupled nonlinear calculation, all those damper configurations leading to low damping performance. This paper continues this effort by applying pre-optimization to determine a damper configuration which will not jam, roll or detach under any in-plane platform kinematics (i.e. blade bending modes). Once the candidate damper configuration has been found, the damper equilibrium equations are solved by using both the multi-harmonic balance (MHB) method and the direct time integration (DTI) to the purpose of finding the correct number of Fourier terms to represent displacements and contact forces. It is shown that, contrarily to non-preoptimized dampers which may display an erratic behavior, one harmonic term together with the static term ensure accurate results. These findings are confirmed by a state-of-the-art code for the calculation of the nonlinear forced response of a damper coupled to two blades. Experimental FRFs of the test case with a nominal damper are available for comparison. The comparison of different damper configurations offers a "high level" validation of the pre-optimization procedure and highlights the strong influence of the blades mode of vibration on the damper effectiveness. It is shown that the pre-optimized damper is not only the most effective, but also the one that leads to a faster and more flexible calculation.
TOPICS: Dampers, Optimization, Blades, Vibration, Damping, Design, Kinematics, Turbine blades, Equilibrium (Physics)
Martin White, Christos N. Markides and A.I. Sayma
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038754
In this paper the effect of working fluid replacement within an organic Rankine cycle turbine is investigated by evaluating the performance of two supersonic stators operating with different working fluids. After designing the two stators, intended for operation with R245fa and Toluene working fluids with stator exit Mach numbers of 1.4 and 1.7 respectively, the performance of each stator is evaluated using ANSYS CFX. It is then hypothesised that the stator design points can be scaled to alternative working fluids by conserving the Prandtl-Meyer function and the polytropic index within the nozzle. A scaling method is developed and further CFD simulations for the scaled operating points verify that the Mach number distributions within the stator, and the non-dimensional velocity triangles at the stator exit, remain unchanged. This confirms that the method developed can predict stator performance following a change in the working fluid. Finally, a study investigating the effect of working fluid replacement on the thermodynamic cycle is completed. The results show that the same turbine could be used in different systems with power outputs varying between 17 and 112 kW, suggesting the potential of matching the same turbine to multiple heat sources by tailoring the working fluid selected.
TOPICS: Fluids, Turbines, Organic Rankine cycle, Stators, Mach number, Design, Engineering simulation, Nozzles, Heat, Simulation, Thermodynamic cycles, Computational fluid dynamics
Jonas Lauridsen and Ilmar F. Santos
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038755
Significant dynamic forces can be generated by annular seals in rotordynamics and can under certain conditions destabilize the system leading to machine failure. Mathematical modelling of dynamic seal forces are still challenging, especially for multiphase fluids and for seals with complex geometries. This results in much uncertainty in the estimation of the dynamic seal forces which often leads to unexpected system behaviour. This paper presents the results of a method suitable for on-site identification of uncertain dynamic annular seal forces in rotordynamic systems supported by Active Magnetic Bearings (AMB). An excitation current is applied through the AMBs to obtain perturbation forces and a system response, from which, the seal coefficients are extracted by utilizing optimization and a-priori information about the mathematical model structure and its known system dynamics. As a study case, the method is applied to a full-scale test-facility supported by two radial AMBs interacting with one annular center mounted test-seal. Specifically, the dynamic behaviour of a smooth annular seal with high preswirl and large clearance is investigated in this study for different excitation frequencies and differential pressures across the seal. The seal coefficients are extracted and a global model on reduced state-space modal form are obtained using the identification process. The global model can be used to update the model based controller to improve the performance of the overall system. This could potentially be implemented in all rotordynamic systems supported by AMBs and subjected to seal forces or other fluid film forces.
TOPICS: Turbochargers, Machinery, Magnetic bearings, Excitation, Fluids, Test facilities, Uncertainty, Control equipment, System dynamics, Clearances (Engineering), Modeling, Optimization, Rotordynamics, Failure, Fluid films
Hui Tang, Mark R Puttock-Brown and J. Michael Owen
J. Eng. Gas Turbines Power   doi: 10.1115/1.4038756
The buoyancy-induced flow and heat transfer inside the compressor rotors of gas-turbine engines affects the stresses and radial growth of the compressor discs, and it also causes a temperature rise in the axial throughflow of cooling air through the centre of the discs. In turn, the radial growth of the discs affects the radial clearance between the rotating compressor blades and the surrounding stationary casing. The calculation of this clearance is extremely important, particularly in aeroengines where the increase in pressure ratios results in a decrease in the size of the blades. In this paper, a published theoretical model - based on buoyancy-induced laminar Ekman-layer flow on the rotating discs - is extended to include laminar free convection from the compressor shroud and forced convection between the bore of the discs and the axial throughflow. The predicted heat transfer from these three surfaces is then used to calculate the temperature rise of the throughflow. The predicted temperatures and Nusselt numbers are compared with measurements made in a multi-cavity compressor rig, and mainly good agreement is achieved for a range of Rossby, Reynolds and Grashof numbers representative of those found in aeroengine compressors. Owing to compressibility effects in the fluid core between the discs - and as previously predicted - increasing rotational speed can result in an increase in the core temperature and a consequent decrease in the Nusselt numbers from the discs and shroud.
TOPICS: Flow (Dynamics), Buoyancy, Heat transfer, Rotors, Compressors, Disks, Temperature, Blades, Clearances (Engineering), Ekman dynamics, Forced convection, Gas turbines, Natural convection, Cavities, Rotating Disks, Pressure, Compressibility, Cooling, Fluids, Engines, Stress
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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

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