Accepted Manuscripts

Yoichi Niki, Yoshifuru Nitta, Hidenori Sekiguchi and Koichi Hirata
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042507
The use of NH3 as an alternative fuel for internal combustion engines has been focused, because NH3 is known as a H2 carrier and its combustion does not produce CO2 causing global warming. There are some reports that unburned NH3 and N2O appear in exhaust gas, when NH3 is used as a fuel internal combustion engines. NH3 has toxic and N2O is one of the greenhouse gases. These emissions should be reduced. It has been also pointed out that exhaust gas after treatments and/or injection strategies can be effective to reduce these emissions. In this study, NH3 combustion processes in the diesel engine were investigated from the experimental results. Based on the investigations, a pilot or post injection was conducted to reduce emissions of NH3 and N2O. In this paper, it is shown firstly the experimental results of the combustion and exhaust emission characteristics on the conventional diesel engine mixed NH3 gas into intake air. NH3 and N2O emissions are then verified by analyzing the exhaust gas. Next, NH3 combustion processes in the diesel engine are considered from the experimental results. It reports on the effects of a pilot and post diesel fuel injection on NH3 and N2O production processes. Finally, the experimental results suggest that the multiple injections can be one of the methods to reduce NH3 emissions without N2O production as side effect.
TOPICS: Diesel, Diesel engines, Emissions, Exhaust systems, Combustion, Fuels, Internal combustion engines, Carbon dioxide, Manufacturing, Gases, Climate change
Hidenori Arisawa, Yuji Shinoda, Mitsuaki Tanaka, Tatsuhiko Goi, Hirofumi Akahori and Mamoru Yoshitomi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042509
Reducing the fluid dynamic power loss for increasing speed is critical for the development of highly efficient high-speed aircraft engine gearing. In this study, the fluid dynamic loss was experimentally performed using a precise friction loss management technique along a vacuum pump in the gearbox. The experimental fluid dynamic loss could be classified as either "oil jet acceleration loss and oil reacceleration loss based on the conservation law of momentum for a point mass" or "oil churning loss and windage loss based on the conservation law of momentum for an incompressible continuum." Windage loss and oil dynamic loss (i.e., the summation of oil jet acceleration loss, oil reacceleration loss, and oil churning loss) were modeled to develop equations for a loss prediction. The equations of the windage loss are pressure loss of flow passing through the side clearance of the gears and energy loss caused by the vortex generation in the cavity between tooth valleys Oil dynamic loss was determined by multiplying the oil jet acceleration loss by an empirical coefficient. The results of the loss prediction equations agree with the experimental results, demonstrating the validity of the proposed model of the fluid dynamic loss.
TOPICS: Fluids, Gears, Modeling, Momentum, Flow (Dynamics), Friction, Pressure, Vortices, Cavities, Vacuum pumps, Aircraft engines, Mechanical drives, Energy dissipation, Clearances (Engineering)
Jinlong Liu and Cosmin E. Dumitrescu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042501
Increased utilization of natural-gas (NG) in the transportation sector can decrease the use of petroleum-based fuels and reduce greenhouse-gas emissions. Heavy-duty diesel engines retrofitted to NG spark ignition (SI) can achieve higher efficiencies and low NOX, CO, and HC emissions when operated under lean-burn conditions. To investigate the SI lean-burn combustion phenomena in a bowl-in-piston combustion chamber, a conventional heavy-duty direct-injection CI engine was converted to SI operation by replacing the fuel injector with a spark plug and by fumigating NG in the intake manifold. Steady-state engine experiments and numerical simulations were performed at several operating conditions that changed spark timing, engine speed, and mixture equivalence ratio. Results suggested a two-zone NG combustion inside the diesel-like combustion chamber. More frequent and significant late burn (including double-peak heat release rate) was observed for advanced spark timing. This was due to the chamber geometry affecting the local flame speed, which resulted in a faster and thicker flame in the bowl but a slower and thinner flame in the squish volume. Good combustion stability (COVIMEP < 3 %), moderate rate of pressure rise, and lack of knocking showed promise for heavy-duty CI engines converted to NG SI operation.
TOPICS: Natural gas, Ignition, Diesel engines, Flames, Combustion, Engines, Combustion chambers, Emissions, Intake manifolds, Geometry, Petroleum, Pistons, Steady state, Fuel injectors, Nitrogen oxides, Diluents, Transportation systems, Diesel, Fuels, Computer simulation, Pressure, Stability, Heat
Daniel Moëll, Andreas Lantz, Karl Bengtson, Daniel Lörstad, Annika Lindholm and Xue-Song Bai
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042473
Large eddy simulations (LES) and experiments (OH-PLIF and pressure transducer) have been carried out on a gas turbine burner fitted to an atmospheric combustion rig. This burner, from the Siemens SGT-800 gas turbine, is a low NOx, partially premixed burner, where pre-heat air temperature, flame temperature and pressure drop across the burner are kept similar to engine full load conditions. The large eddy simulations are based on a flamelet generated manifold approach for representing the chemistry and the Smagorinsky model for sub-grid turbulence. The experimental data and simulation data are in good agreement, both in terms of time averaged as well as time resolved quantities. From the experiments and LES, three bands of frequencies of pressure fluctuations with high power spectral density are found in the combustion chamber. The first two bands are found to be axial pressure modes, triggered by coherent flow motions from the burner, such as the flame stabilization location and the precessing vortex core (PVC). The third band is found to be a cross flow directional mode interacting with two of the four combustion chamber walls in the square section of the combustion chamber, triggered from general flow motions. This study shows that LES of real gas turbine components is feasible and that the results give important insight into the flow, flame and acoustic interactions in a specific combustion system.
TOPICS: Combustion, Dynamics (Mechanics), Gas turbines, Experimental analysis, Large eddy simulation, Flames, Combustion chambers, Flow (Dynamics), Pressure, Temperature, Cross-flow, Flamelet generated manifold, Pressure drop, Nitrogen oxides, Heat, Combustion systems, Vortices, Chemistry, Turbulence, Acoustics, Engines, Pressure transducers, Simulation, Stress, Fluctuations (Physics), Spectral energy distribution
Enrico Munari, Gianluca Delia, Mirko Morini, Michele Pinelli and Pier Ruggero Spina
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042474
Wet compression is a strategy adopted to increase the power output of gas turbines, with respect to dry conditions, usually also incrementing the operating range of the compressor. However, stall and surge are two aerodynamic instabilities which depend on many factors, and they are expected to occur even in wet compression at low flow rates. Despite the many studies carried out in the last 80 years, literature does not offer many works concerning these instability phenomena in wet compression. In this paper, an experimental analysis of stall and surge in wet compression conditions is carried out on an axial-centrifugal compressor installed in an existing test rig at the Engineering Department of the University of Ferrara. The intake duct was implemented with a water injection system which allows the uniform mixing of air and water before the compressor inlet. The control and data acquisition system of the test bench was updated with new hardware and software to obtain faster data sampling. Transient and steady-state tests were carried out to make a comparison with the experimental results in dry conditions. The analysis was carried out using traditional thermodynamic sensors, by means of both classic post-processing techniques, and cyclostationary analysis. The aim is to i) evaluate the influence of wet compression on the stable performance of the compressor ii) qualitatively identify the characteristics of stall and surge in wet compression and iii) demonstrate the reliability of cyclostationary analysis in wet compression conditions for stall and surge analysis.
TOPICS: Compression, Surges, Compressors, Reliability, Hardware, Transients (Dynamics), Gas turbines, Underground injection, Computer software, Ducts, Experimental analysis, Steady state, Water, Data acquisition systems, Flow (Dynamics), Sensors
Shuxian CHEN, Zhigang LI and Jun LI
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042422
This paper presents a numerical investigation on the sealing effectiveness and unsteady flow field of a 1.5-stage turbine with the front and aft wheel-space cavities. The sealing effectiveness and flow structure are studied by solving three dimensional Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations and SST turbulence model. The numerical pressure and swirl ratio distributions in cavities with two computational models are compared with experimental data to determine the position of stationary/rotating domain interface. The unsteady results agree well with experimental data. The effects of coolant flow rates on the sealing effectiveness and the flow field of the rim seal at the front and aft cavities are investigated. The obtained results show that the sealing effectiveness of the rim seal at the aft cavity is much larger than that of the rim seal at the front cavity at the same coolant flow rate. The less mainstream pressure fluctuation near the aft rim seal clearance and the clockwise vortex due to the pumping effect in the aft rim seal leads to this result. The mainstream pressure fluctuation downstream of the blade and the sealing effectiveness of the rim seal at the aft cavity under five operating conditions are computed. It shows that the square root of the mainstream pressure fluctuation amplitude downstream of the blade is proportional to the mainstream flow rate. The increase of the mainstream flow results in gradually decrease of the sealing effectiveness of the rim seal at the aft cavity.
TOPICS: Sealing (Process), Turbines, Unsteady flow, Cavities, Flow (Dynamics), Pressure, Blades, Coolants, Clearances (Engineering), Turbulence, Vortices, Wheels
Meijie Zhang, Xinqian Zheng, Qiangqiang Huang and Zhenzhong Sun
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042419
Compression systems are widely employed in gas turbine engines, turbocharged engines and industry compression plants. The stable work of compression systems is an essential precondition for engine performance and safety. A compression system in practice usually consists of upstream and downstream pipes, compressors, plenums and throttles. When a compression system encounters the surge, the flows in the compressor present complex three-dimensional patterns but the flows of other components might present relatively simple one-dimensional patterns. Based on these flow characteristics, this paper proposes a novel simulation method, where one-dimensional and three-dimensional (1D-3D) calculations are coupled, to predict the surge boundary of centrifugal compressors. To validate this method, a high-speed centrifugal compressor is studied both by the proposed 1D-3D coupled method and experimentally. The results show the differences between predicted and experimentally determined stable flow range are lower than 5% until the Mach number of blade outlet tip tangential velocity reaches around 1.3. Besides, this method can correctly predict the instantaneous compressor performance during the surge cycle, so it can also be used to explore the surge mechanism and evaluate the blade dynamic force response in the future.
TOPICS: Compressors, Surges, Compression, Flow (Dynamics), Blades, Cycles, Turbocharged engines, Mach number, Safety, Engines, Simulation, Gas turbines, Pipes
Hans Meeus, Jakob Fiszer, Gabriël-Mathieu Van De Velde, Björn Verrelst, Dirk Lefeber, Patrick Guillaume and Wim Desmet
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042418
Squeeze film dampers are widely used to dissipate mechanical energy caused by rotor vibrations. Especially turbomachine rotors, supported on little damped rolling element bearings, are primarily sensitive to unbalance excitation and thus high amplitude vibrations. To ensure safe operation, potential failure modes, such as an oil starved damper state, need to be well examined prior to the introduction in the ultimate industrial application. Hence, the aim of this research project is to evaluate the performance of the rotor support for a complete oil starvation of the squeeze film damper. An academic rotor dynamic test bench has been developed and briefly presented. Experimental testing has been conducted for two static radial load cases resembling the full load and idle condition of a certain turbomachine. Evidently, the measurement results exposed severe vibration problems. Even a split first whirl mode arises due to a pronounced anisotropic bearing stiffness. Moreover, for the least radially loaded bearing highly nonlinear behavior emerged at elevated unbalance excitation. Consequently, the rollers start to rattle which will have a negative effect on the overall bearing lifetime. To explain the nature of the nonlinear behavior, advanced quasi-static bearing simulations are exploited. A number of possible solutions are proposed in order to help mitigate the vibration issues.
TOPICS: Dampers, Roller bearings, Bearings, Vibration, Rotors, Turbomachinery, Stress, Excitation, Anisotropy, Simulation, Engineering simulation, Failure mechanisms, Rotor vibration, Whirls, Testing, Rollers, Rolling bearings, Stiffness
Jiabo Zhang, Anhao Zhong, Zhen Huang and Dong Han
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042412
A theoretical analysis based on the second-law thermodynamics was conducted for the ammonia/hydrogen/air premixed flames at different initial pressures. The irreversibility causing exergy losses in premixed flames were divided into five parts, namely heat conduction, mass diffusion, viscous dissipation, chemical reaction and incomplete combustion, respectively. The results revealed that as hydrogen percentage in fuel blends increased from 0% to 100%, the total exergy losses decreased. Specifically, the exergy losses induced by heat conduction and mass diffusion decreased with increased hydrogen percentage. The exergy loss induced by incomplete combustion increased with hydrogen addition, as more incomplete combustion products, such as H2, H and OH, were generated with increased hydrogen percentage. The exergy loss by chemical reactions first decreased and then increased with increased hydrogen percentage, which was attributed to the combination effects of increased entropy generation rate and reduced flame thickness. Compared to the other four sources, the exergy loss induced by viscous dissipation was negligible. Furthermore, at the elevated pressure of 5 atm, the effects of hydrogen blending were similar with those at the atmospheric condition. However, the exergy losses by heat conduction and mass diffusion increased while the exergy losses by chemical reaction and incomplete combustion were both reduced, with the overall exergy loss decreased by 1-2% as the pressure increased from 1 atm to 5 atm.
TOPICS: Fuels, Flames, Hydrogen, Exergy, Combustion, Diffusion (Physics), Heat conduction, Chemical reactions, Energy dissipation, Pressure, Thermodynamics, Entropy, Theoretical analysis
Parthiv Shah, Andrew White, Dan Hensley, Dimitri Papamoschou and Havard Vold
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042395
Imaging of aeroacoustic noise sources is routinely accomplished with geometrically fixed phased arrays of microphones. Several decades of research have gone into improvement and optimization of sensor layouts, selection of basis models, and deconvolution algorithms to produce sharper and more localized images of sound-producing regions in space. This paper explores an extension to conventional phased array measurements that uses slowly, continuously moving microphone arrays with and without coupling to rigid fixed arrays to improve image quality and better describe noise mechanisms on turbofan engine sources such as jet exhausts and turbomachinery components. Three approaches are compared in the paper: fixed receiver beamforming (FRBF), continuous-scan beamforming (CSBF), and multireference CSBF (MRCSBF). The third takes advantage of transfer function matrices formed between fixed and moving sensors to achieve effective virtual arrays with spatial density one to two orders of magnitude higher, with practical sensor budgets and scan speeds. The MRCSBF technique produces array sidelobe rejection that approaches the theoretical array pattern of a continuous 2-D aperture. The implications of this finding are that better source localization may be achieved with conventional delay and sum (DAS) beamforming (BF) with practical sensor budgets, and that an improved starting image of the sound source can be provided to deconvolution algorithms. These findings are demonstrated on analytical and experimental examples from a low-cost rotating phased array using point sound sources, as well as linear scanning array experiments of an impinging jets point source and a near-sonic jet nozzle exhaust.
TOPICS: Acoustics, Engines, Testing, Turbofans, Sensors, Noise (Sound), Algorithms, Nozzles, Optimization, Transfer functions, Jets, Density, Data acquisition systems, Delays, Exhaust systems, Microphone arrays, Microphones, Turbomachinery, Imaging
Kenny Hu, Xingkai Chi, Tom I-P. Shih, Dr. Minking K. Chyu and Michael E. Crawford
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042332
Steady RANS were performed to examine the ability of four turbulence models - realizable k-e(k-e), shear-stress transport(SST), Reynolds stress model with linear pressure strain(RSM-LPS), and stress-omega RSM(RSM-t?) - to predict the turbulent flow and heat transfer in a trapezoidal U-duct with and without a staggered array of pin fins. Results generated for the heat-transfer coefficient (HTC) were compared with experimental measurements. For the smooth U-duct, the maximum relative error in the averaged HTC in the up-leg is 2.5% for k-e, SST, and RSM-t? and 9% for RSM-LPS. In the turn region, that maximum is 50% for k-e and RSM-LPS, 14.5% for RSM-t?, and 29% for SST. In the down-leg, SST gave the best predictions and RSM-t? being a close second with maximum relative error less than 10%. The ability to predict the separated flow downstream of the turn dominated the performance of the models. For the U-duct with pin fins, SST and RSM-t? predicted the best, and k-e predicted the least accurate HTCs. For k-e, the maximum relative error is about 25%, whereas it is 15% for the SST and RSM-t?, and they occur in the turn. In the turn region, the staggered array of pin fins was found to behave like guide vanes in turning the flow. The pin fins also reduced the size of the separated region just after the turn.
TOPICS: Flow (Dynamics), Heat transfer, Ducts, Reynolds-averaged Navier–Stokes equations, Fins, Errors, Turbulence, Stress, Pressure, Guide vanes, Shear stress
Shyang Maw Lim, Anders Dahlkild and Mihai Mihaescu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042301
This research was primary motivated by limited efforts to understand the effects of secondary flow and flow unsteadiness on the heat transfer and the performance of a turbocharger turbine subjected to pulsatile flow. In this study, we aimed to investigate the influence of exhaust manifold on the flow physics and the performance of its downstream components, including the effects on heat transfer, under engine-like pulsatile flow conditions. Based on the predicted results by Detached Eddy Simulation (DES), qualitative and quantitative flow fields analyses in the scroll and the rotor's inlet were performed, in addition to the quantification of turbine performance by using the flow exergy methodology. With the specified geometry configuration and exhaust valve strategy, our study showed that 1) The exhaust manifold influences the flow field and the heat transfer in the scroll significantly, and 2) Although the exhaust gas blow-down disturbs the relative flow angle at rotor inlet, the consequence on the turbine power is relatively small.
TOPICS: Turbochargers, Turbines, Exhaust manifolds, Flow (Dynamics), Heat transfer, Exhaust systems, Pulsatile flow, Physics, Geometry, Eddies (Fluid dynamics), Engines, Simulation, Valves, Exergy, Rotors
Francesco Crespi, David Sánchez, Tomás Sánchez and Gonzalo S. Martínez
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042304
Previous work by the authors has shown that broader analyses than those typically found in literature (in terms of operating pressures allowed) can yield interesting conclusions with respect to the best candidate cycles for certain applications. This has been tested for the thermodynamic performance (1st and 2nd Laws) but it can also be applied from an economic standpoint. This second approach is introduced in this work where typical operating conditions for CSP applications (current and future generations of solar tower plants) are considered (750ºC and 30 MPa). For these, the techno-economic performance of each cycle is assessed in order to identify the most cost-effective layout when it comes to the Overnight Capital Cost. This analysis accounts for the different contributions to the total cost of the plant, including all the major equipment that is usually found in a CSP power plant such as the solar field and thermal energy storage system. The work is thus aimed at providing guidelines to professionals in the area of basic engineering and pre-feasibility study of CSP plants who find themselves in the process of selecting a particular power cycle for a new project (set of specifications and boundary conditions)
TOPICS: Concentrating solar power, Supercritical carbon dioxide, Thermodynamic power cycles, Cycles, Solar energy, Boundary-value problems, Thermal energy storage, Power stations
Christopher Bowen, Nathan Libertowski, Mehdi Mortazavi and Dr. Jeffrey Bons
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042287
The role of temperature on deposition in gas turbine internal cooling geometries is investigated. Single impingement cones are developed by an oversized (6 mm) impinging jet over a range of temperatures and flow velocities using 0-5 µm ARD. Cone size was found to increase with increasing temperature and decrease with increasing velocity. Capture efficiency and cone angle ef- fects are presented, and packing factor data is used as a metric to determine if the contact area (Acont ) for adhesion explains the trends seen with temperature. It is systematically demonstrated that the surface free energy (?) is likely a first order function of temperature in internal deposition for the range of temperatures investigated. Candidate physical mechanisms that may cause in- creased adhesive force at elevated temperatures are identified. Temperature dependent adhesion is added to the OSU Deposition Model which is then used with a simplified morphing approach to match temperature induced blockage patterns in a vane leading edge cooling experiment. This process is improved upon using a full mesh morphing routine and matching two of the experimental deposition cones at varied flow temperatures. The added fidelity that mesh morphing affords is demonstrated.
TOPICS: Temperature, Cooling, Adhesion, Modeling, Turbines, Flow (Dynamics), Adhesives, Packing (Shipments), Packings (Cushioning), Gas turbines
Benoit Cheneau, Aymeric Vié and Sébastien Ducruix
J. Eng. Gas Turbines Power   doi: 10.1115/1.4042205
The aim of the present work is to evaluate the ability of Large Eddy Simulation to predict flame shape and structures in a two-stage two-injection burner representative of new generation staged aeronautical engine: the BIMER burner. This combustor is a unique design because of an additional parameter, the staging factor, which controls the fuel mass flow rate splitting between the two swirl stages. Experiments conducted on the BIMER combustor at atmospheric pressure and for a constant power output have revealed that the shape of the flame changes with the staging factor; this shape also depends on the staging factor evolution history (SFEH). Targeting a single operating point and three staging situations, the objectives are to prove the ability of our simulation strategy to predict the proper shapes by reproducing these stabilization processes and to participate in their explanation, using numerical post-treatments. After validation through comparisons with experiments, our study focuses on these three configurations, two of them only differing by their SFEH. Remarkably, correct flame shapes are obtained numerically for the same operating point, fuel staging factors and SFEH. Qualitative and quantitative comparisons show very satisfactory agreement. In a second step, the three flame shapes are analyzed in depth. The key role played by the central and corner recirculation zones in the flames' existence and stabilization processes is emphasized. An original composition space analysis highlights the combustion regimes observed in these three cases, confirming the distinct stabilization scenarios proposed here for the three operating points.
TOPICS: Flames, Shapes, Combustion chambers, Fuels, Engines, Simulation, Flow (Dynamics), Combustion, Atmospheric pressure, Corners (Structural elements), Design, Large eddy simulation
Tim Allison, Ph.D., Natalie R. Smith, Robert Pelton, Jason C. Wilkes and Sewoong Jung
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041920
Successful implementation of sCO2 power cycles requires high compressor efficiency at the design-point and over a wide operating range in order to maximize cycle power output and maintain stable operation over many transient and part-load conditions. This requirement is particularly true for air-cooled cycles where compressor inlet density is a strong function of inlet temperature that exhibits daily and seasonal variations as well as transient events. To meet these requirements, a novel centrifugal compressor stage design was developed that incorporates multiple range extension features, including a passive recirculating casing treatment and semi-open impeller design. This design was fabricated via direct metal laser sintering and tested in an open-loop test rig in order to validate simulation results and the effectiveness of the casing treatment configuration. Comparison of predicted performance in air and CO2 conditions resulted in a reduced diffuser width for the air test in order to match design velocities and demonstrate the casing treatment. Test results in air show that the casing treatment performance generally matched CFD predictions, demonstrating an operating range of 69% and efficiency above predictions across the entire map. The casing treatment configuration demonstrated performance improvements over a solid wall configuration at low flows, resulting in an effective 14% increase in operating range with a 0.5-point efficiency penalty. The test results are also compared to a traditional fully shrouded impeller with the same flow coefficient and similar head coefficient, showing a 42% range improvement over traditional designs.
TOPICS: Compressors, Supercritical carbon dioxide, Thermodynamic power cycles, Design, Cycles, Flow (Dynamics), Impellers, Transients (Dynamics), Diffusers, Computational fluid dynamics, Temperature, Metals, Lasers, Simulation results, Carbon dioxide, Sintering, Stress, Density
Timothy C. Allison, Ph.D., J. Jeffrey Moore, Douglas Hofer, Meera Towler and J. Michael Thorpe
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041921
Supercritical CO2 power cycles incorporate a unique combination of high fluid pressure, temperature, and density as well as limited component availability (e.g., high-temperature trip valves) that can result in operational challenges, particularly during off-design and transient operation. These conditions and various failure scenarios must be considered and addressed during the facility, component, and control system design phase in order to ensure machinery health and safety during operation. This paper discusses significant findings and resulting design/control requirements from a detailed failure modes and effects analysis that was performed for the 1 MWe-scale supercritical CO2 test loop at Southwest Research Institute, providing insight into design and control requirements for future test facilities and applications. The test loop incorporates a centrifugal pump, axial turboexpander, gas-fired primary heat exchanger, and micro-channel recuperator for testing in a simple recuperated cycle configuration at pressures and temperatures up to 255 bara and 715°C, respectively. The analysis considered off-design operation as well as high-impact failures of turbomachinery and loop components that may require fast shutdowns and blowdowns. The balance between fast shutdowns/blowdowns and the need to manage thermal stresses in the turbomachinery resulted in staged shutdown sequences and impacted the design/control strategies for major loop components and ancillary systems including the fill, vent, and seal supply systems.
TOPICS: Transients (Dynamics), High temperature, Design, Temperature, Failure, Supercritical carbon dioxide, Turbomachinery, Vents, Microchannels, Thermodynamic power cycles, Health and safety, Test facilities, Density, Fluid pressure, Machinery, Control systems, Thermal stresses, Failure mechanisms, Heat exchangers, Testing, Valves, Centrifugal pumps, Cycles
Technical Brief  
Binyang Wu, Zhiqiang Han, Xiaoyang Yu, Shuikai Zhang and Xiaokun Nie
J. Eng. Gas Turbines Power   doi: 10.1115/1.4039461
Matching of a two-stage turbocharging system is important for high efficiency engines because the turbocharger is the most effective method of exhaust heat recovery. In this study, we propose a method to match a two-stage turbocharging system for high efficiency over the entire range of operational conditions. Air flow is an important parameter because it influences combustion efficiency and heat load performance. First, the thermodynamic parameters of the engine and the turbocharging system are calculated in eight steps for selecting and matching the turbochargers. Then, by designing the intercooler intensity, distribution of pressure ratio, and compressor operational efficiency, it is ensured that the turbochargers not only meet the air flow requirements but also operate with high efficiency. The concept of minimum total drive power of the compressors is introduced at a certain boost pressure. It is found that the distribution of pressure ratio of the high- and low-pressure turbocharger should be regulated according to the engine speed by varying the rack position of the variable geometry turbocharger (VGT) to obtain the minimum total drive work. It is verified that two-stage turbochargers have high efficiency over the entire range of operational conditions by experimental research. Compared with the original engine torque, low-speed torque is improved by more than 10%, and the engine low fuel consumption area is broadened.
TOPICS: Engines, Turbochargers, Pressure, Torque, Compressors, Air flow, Heat recovery, Stress, Design, Exhaust systems, Geometry, Fuel consumption, Heat, Combustion
Xu Rui, Long Yun, Yaoyu Hu, Junlian Yin and Dezhong Wang
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041756
Reactor coolant pump is one of the most important equipment of the coolant loop in a pressurized water reactor system. Its safety re-lies on the characteristics of the rotordynamic system. For a canned motor reactor coolant pump, the liquid coolant fills up the clearance between the metal shields of the rotor and stator inside the canned motor, forming a long clearance flow. The fluid induced forces of the clearance flow in canned motor reactor coolant pump and their effects on the rotordynamic characteristics of the pump are numeri-cally and experimentally analyzed in this work. A transient computational fluid dynamics (CFD) method has been used to investigate the fluid induced force of the clearance. A vertical experiment rig has also been established for the purpose of measuring the fluid in-duced forces. Fluid induced forces of clearance flow with various whirl frequencies and various boundary conditions are obtained through the CFD method and the experiment. Results show that clearance flow brings large mass coefficient into the rotordynamic system and the direct stiffness coefficient is negative under the normal operating condition. The rotordynamic stability of canned motor reactor coolant pump does not deteriorate despite the existence of significant cross-coupled stiffness coefficient from the fluid induced forces of the clearance flow.
TOPICS: Flow (Dynamics), Fluids, Engines, Motors, Clearances (Engineering), Pumps, Nuclear reactor coolants, Computational fluid dynamics, Stiffness, Coolants, Transients (Dynamics), Metals, Safety, Whirls, Pressurized water reactors, Stators, Rotors, Boundary-value problems, Stability
Thomas Kerr, Andrew Crandall, Dara Childs and Adolfo Delgado
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041654
This paper introduces a test facility specifically designed to measure the axial stiffness and damping coefficients of an oillubricated thrust collar (TC). The geometry, load, and speeds of the test facility are representative of a production integrally geared compressor (IGC). Separate electric motors spin the shafts according to an assumed gear ratio, a pneumatic air piston loader provides a non-contacting, static thrust force, a remotelycontrolled impact hammer delivers a perturbation force, and eddy-current motion probes record the resulting vibration. The paper uses a one degree of freedom (1DOF) axial motion model that neglects the static and dynamic stiffness of the bull wheel and presents estimates of the TC oil-film dynamic coefficients for pinion spin speeds between 5 and 10 krpm, and static loads between 200 and 400 N, using time-domain (log-dec and damped period) and static load-deflection techniques. The measurements show that the TC oil-film develops appreciable stiffness (tens of MN/m), and the 1DOF model used here is inadequate for higher loads. Axial runout on the interfacing surfaces of the test facility TC and bull wheel complicates parameter identification, but time-domain averaging effectively attenuates the runout while preserving the transient vibration that results from the impact hammer. Measurements of the TC oil-film stiffness, damping and virtual mass coefficients are useful to machinery OEMs or end-users seeking to predict or diagnose subsynchronous vibration in their machine that might be TC related.
TOPICS: Compressors, Thrust, Stress, Stiffness, Test facilities, Vibration, Particle spin, Hammers, Spin (Aerodynamics), Rotation, Machinery, Wheels, Damping, Gears, Eddies (Fluid dynamics), Electric motors, Transients (Dynamics), Degrees of freedom, Eddy currents (Electricity), Deflection, Geometry, Pistons, Probes

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