Accepted Manuscripts

Juan Pablo Gomez Montoya, Andres Amell and Daniel B. Olsen
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041755
This research evaluated the operational conditions for a diesel engine with high compression ratio (CR) converted to spark ignition (SI), under stable combustion conditions close to the knocking threshold. The main fuel used in the engine was biogas, which was blended with natural gas, propane and hydrogen to improve combustion properties and using two equivalence ratios. The engine limit to test the maximum output power was using the knocking threshold, just below the knocking threshold the output power and generating efficiency are the highest possible for each blend. Leaner mixtures increased the engine knocking tendency because the required increase in the % throttle reduced the pressure drop at the inlet stroke and increased the mixture pressure at the end of the compression stroke, which finally reduced the ignition delay time of the end gas and increased the knocking tendency of the engine for all the blends. Therefore, the output power should be decreased to operate the engine below to the knocking threshold. Purified biogas achieved the highest output power and generating efficiency compared with the other blends and the original diesel operation, this blend was operated with five equivalence ratios. This alternative fuel blend exhibits an optimal balance between knocking resistance, low heating value, flame speed and energy density.
TOPICS: Biogas, Natural gas, Hydrogen, Spark-ignition engine, Engines, Compression, Combustion, Fuels, Density, Pressure, Diesel, Diesel engines, Flames, Heating, Ignition delay, Ignition, Pressure drop
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
Natalie R. Smith, Tim Allison, Ph.D., Ph.D., Jason C. Wilkes, Christopher Clarke and Michael Cave
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041740
Full-thermal heat-soak of machinery is vital to acquiring accurate aerodynamic performance data, but this process often requires significant testing time to allow for all facility components to reach a steady state temperature. Even still, there is the potential for heat loss in a well-insulated facility, and this can lead to inaccurate results. The implementation of a torquemeter to calculate performance metrics, such as isentropic efficiency, has two potential advantages: 1) the method is not susceptible to effects due to thermal heat loss in the facility, and 2) a torquemeter directly measures actual torque, and thus work, input, which eliminates the need to fully heat-soak to measure the actual enthalpy rise of the gas. This paper presents a comparison of aerodynamic performance metrics calculated both from data acquired with thermal measurements as well as from a torquemeter. These tests were conducted over five speedlines for a shrouded impeller in the Southwest Research Institute Single Stage Test Rig facility. Isentropic efficiency calculated from the torquemeter was approximately 1-2 efficiency points lower than the isentropic efficiency based on thermal measurements. This corresponds to approximately 0.5-1°C in heat loss in the discharge collector and piping. Furthermore, observations from three full-thermal heat-soak points indicate the significant difference in time required to reach steady state performance within measurement uncertainty tolerances between the torque-based and thermal-based methods. This comparison, while largely suspected, has not yet been studied in previous publications.
TOPICS: Torquemeters, Compressor impellers, Heat losses, Heat, Steady state, Torque, Measurement uncertainty, Temperature, Machinery, Impellers, Pipes, Testing, Enthalpy
Yeshaswini Emmi, Andreas Fiolitakis, Manfred Aigner, Franklin Genin and Khawar Syed
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041726
A new model approach is presented in this work for including convective wall heat losses in the Direct Quadrature Method of Moments (DQMoM) approach, which is used here to solve the transport equation of the one-point, one-time joint thermochemical probability density function (PDF). This is of particular interest in the context of designing industrial combustors, where wall heat losses play a crucial role. In the present work, the novel method is derived for the first time and validated against experimental data for the thermal entrance region of a pipe. The impact of varying model-specific boundary conditions is analysed. It is then used to simulate the turbulent reacting flow of a confined methane jet flame. The simulations are carried out using the DLR in-house Computational Fluid Dynamics (CFD) code THETA. It is found that the DQMoM approach presented here agrees well with the experimental data and ratifies the use of the new convective wall heat losses model.
TOPICS: Turbulence, Simulation, Engineering simulation, Heat losses, Chemically reactive flow, Computational fluid dynamics, Design, Pipes, Boundary-value problems, Combustion chambers, Density, Flow (Dynamics), Entrance region, Flames, Methane, Method of moments, Probability
Zhixiong Li, Kai Goebel and Dazhong Wu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041674
Degradation modeling and prediction of remaining useful life (RUL) is crucial in prognostics and health management of aircraft engines. While model-based methods have been introduced to predict the RUL of aircraft engines, little research has been reported on estimating the RUL of aircraft engines using data-driven predictive modeling methods. The objective of this study is to introduce an ensemble learning-based prognostics approach to damage propagation modeling and prognostics of failures in aircraft engines. This ensemble learning algorithm combines multiple base learners, including random forests (RFs), classification and regression tree (CART), recurrent neural networks (RNN), autoregressive (AR) model, adaptive network-based fuzzy inference system (ANFIS), relevance vector machine (RVM), and elastic net (EN). To make accurate predictions, the particle swarm optimization (PSO) and sequential quadratic optimization (SQP) methods are used to determine optimum weights that are assigned to the base learners. The predictive model trained by the ensemble learning algorithm is demonstrated on the data generated by the Commercial Modular Aero-Propulsion System Simulation (C-MAPSS) tool. Experimental results have shown that the ensemble learning algorithm predicts the RUL of the aircraft engines with considerable robustness as well as outperforms other reported prognostic methods.
TOPICS: Service life (Equipment), Modeling, Aircraft engines, Algorithms, Particle swarm optimization, Robustness, Damage, Optimization, Artificial neural networks, Failure, Propulsion, Machinery, Simulation
Emiliano Pipitone and Stefano Beccari
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041675
The introduction of natural gas (NG) in the road transport market is proceeding through bi-fuel vehicles, which, endowed of a double injection system, can run either with gasoline or with NG. A third possibility is the simultaneous combustion of NG and gasoline, called Double-Fuel (DF) combustion: the addition of methane to gasoline allows to run the engine with stoichiometric air even at full load, without knocking phenomena, increasing engine efficiency of about 26% and cutting pollutant emissions by 90%. The introduction of DF combustion into series production vehicles requires however proper engine calibration (i.e. determination of DF injection and spark timing maps), a process which is drastically shortened by the use of computer simulations (with a 0D two zone approach for in-cylinder processes). An original knock onset prediction model is here proposed to be employed in zero-dimensional simulations for knock-safe performances optimization of engines fueled by gasoline-NG mixtures or gasoline-methane mixtures. The model takes into account the NTC behavior of fuels and has been calibrated using a considerable amount of knocking in-cylinder pressure cycles acquired on a Cooperative Fuel Research engine widely varying compression ratio, inlet temperature, spark advance and fuel mixture composition, thus giving the model a general validity for the simulation of naturally aspirated or supercharged engines. As a result, the auto-ignition onset is predicted with maximum and mean error of 4.5 and 1.4 deg respectively, which is a negligible quantity from an engine control standpoint.
TOPICS: Fuels, Ignition, Methane, Spark-ignition engine, Gasoline, Engines, Combustion, Simulation, Cylinders, Vehicles, Calibration, Compression, Cutting, Cycles, Errors, Computer simulation, Stress, Natural gas, Optimization, Mass production, Pressure, Temperature, Road transport, Pollution, Supercharged engines, Emissions
Lorenzo Mazzei, Stefano Puggelli, Davide Bertini, Antonio Andreini, Bruno Facchini, Ignazio Vitale and Antonio Santoriello
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041676
Lean burn combustion is increasing its popularity in the aeronautical framework due to its potential in reducing drastically pollutant emissions (NOx and soot in particular). Its implementation however involves significant issues related to the increased amount of air dedicated to the combustion process, demanding the redesign of injection and cooling systems. Also the conditions at the combustor exit are a concern, as high turbulence, residual swirl and the impossibility to adjust the temperature profile with dilution holes determine a harsher environment for nozzle guide vanes. This work describes the final stages of the design of an aeronautical effusion-cooled lean burn combustor. Full annular tests were carried out to measure temperature profiles and emissions (CO and NOx) at the combustor exit. Different operating conditions of the ICAO cycle were tested, considering Idle, Cruise, Approach and Take-Off. Scale-adaptive simulations with the Flamelet Generated Manifold combustion model were performed to extend the validation of the employed CFD methodology and to reproduce the experimental data in terms of RTDF/OTDF profiles as well as emission indexes. The satisfactory agreement paved the way to an exploitation of the methodology to provide a deeper understanding of the flow physics within the combustion chamber, highlighting the impact of the different operating conditions on flame, spray evolution and pollutant formation.
TOPICS: Combustion chambers, Emissions, Combustion, Temperature profiles, Pollution, Nitrogen oxides, Physics, Flow (Dynamics), Cooling systems, Turbulence, Simulation, Computational fluid dynamics, Design, Engineering simulation, Sprays, Cycles, Flames, Soot, Nozzle guide vanes, Flamelet generated manifold
Ping Wang, Qian Yu, Prashant Shrotriya and Mingmin Chen
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041656
In the present work, the fluctuations of equivalence ratio in the PRECCINSTA combustor are investigated via large eddy simulations (LES). Four isothermal flow cases with different combinations of global equivalence ratios (0.7 or 0.83) and grids (1.2 or 1.8 million cells) are simulated to study the mixing process of air with methane, which is injected into the inlet channel through small holes. It is shown that the fluctuations of equivalence ratio are very large, and their ranges are [0.4, 1.3] and [0.3, 1.2] for case 0.83 and 0.7, respectively. For simulating turbulent partially premixed flames in this burner with the well-known dynamically thickened flame combustion model, a suitable multi-step reaction mechanism should be chosen aforehand. To do that, laminar premixed flames of 15 different equivalence ratios are calculated using three different methane/air reaction mechanisms: 2S_CH4_BFER, 2sCM2 reduced mechanisms and GRI-Mech 3.0 detailed reaction mechanism. The variations of flame temperature, flame speed and thickness of the laminar flames with the equivalence ratios are compared in detail. It is demonstrated that the applicative equivalence ratio range for the 2S_CH4_BFER mechanism is [0.5, 1.3], which is larger than that of the 2sCM2 mechanism [0.5, 1.2]. Therefore, it is recommended to use the 2S_CH4_BFER scheme to simulate the partially premixed flames in the PRECCINSTA combustion chamber.
TOPICS: Fluctuations (Physics), Combustion chambers, Gas turbines, Numerical analysis, Flames, Methane, Large eddy simulation, Flow (Dynamics), Temperature, Combustion, Turbulence
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
Florence Nyssen and Alain Batailly
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041647
In modern turbomachine designs, the nominal clearances between rotating bladed-disks and their surrounding casing are reduced to improve aerodynamic performances of the engine. This clearance reduction increases the risk of contacts between components and may lead to hazardous interaction phenomena. A common technical solution to mitigate such interactions consists in the deposition of an abradable coating along the casing inner surface. This enhances the engine efficiency while ensuring operational safety. However, contact interactions between blade-tips and an abradable layer may yield unexpected wear removal phenomena. The aim of this work is to investigate the numerical modeling of thermal effects within the abradable layer during contact interactions and compare it with experimental data. A dedicated thermal finite element mesh is employed. A weak thermo-mechanical coupling is assumed: thermal effects affect the system mechanics, but the mechanical deformation of the elements has no effect on temperatures. Weak coupling is well appropriated in the case of rapid dynamics using small time step and explicit resolution schemes. Moreover, only heat transfer by conduction is considered in this work. To reduce computational times, a coarser spatial discretization is used for the thermal mesh comparing to the mechanical one. The time step used to compute the temperature evolution is larger than the one used for the mechanical iterations since the time constant of thermal effect is larger than contact events. The proposed numerical modeling strategy is applied on an industrial blade to analyze the impact of thermal effects on the blade's dynamics.
TOPICS: Wear, Coating processes, Coatings, Modeling, Thermomechanics, Aircraft engines, Temperature effects, Blades, Temperature, Dynamics (Mechanics), Computer simulation, Engines, Heat conduction, Resolution (Optics), Deformation, Heat transfer, Turbomachinery, Disks, Clearances (Engineering), Finite element analysis, Safety, Risk
Behzad Zamanian Yazdi and Daejong Kim
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041646
Air foil bearings (AFBs) are introduced as promising bearings for oil-free turbomachinery applications. AFBs provide reliable operation at high speed and high temperature with negligible power loss. Hybrid Air Foil Bearing (HAFB) technology utilizes the radial injection of externally pressurized air into the traditional hydrodynamic AFB's film thickness through orifices attached to the top foil. Previous studies have reported enhancement in the rotordynamic stability of HAFBs compared to traditional hydrodynamic AFBs. HAFBs have several orifices distributed in the circumferential direction. In this study, the effect of the circumferential location of radial injection on the rotordynamic performance of the rotor-HAFB is studied. Analytical and experimental evaluations of the rotordynamic performance of a rotor supported by two single-pad HAFBs are presented. Parametric studies are conducted using three sets of single-pad HAFBs. The circumferential locations of orifices are different for each set. The presented simulation analyses consist of time-domain orbit simulation and frequency-domain modal analysis. Imbalance responses of rotor-HAFB were measured with various orifice locations and the results agree well with predictions. Comparison of the rotordynamic performance of HAFBs with different orifice configurations demonstrate substantial improvement in rotordynamic stability as well as enhancement in the stiffness and damping coefficients of HAFBs by choosing the best circumferential location for radial injection to control rotor eccentricity and attitude angle.
TOPICS: Foil bearings, Rotors, Orifices, Stability, Simulation, Bearings, Damping, Simulation analysis, Stiffness, Turbomachinery, High temperature, Film thickness, Modal analysis
Chongfei Duan, Hisataka Fukushima, Kiyoshi Segawa, Takanori Shibata and Hidetoshi Fujii
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041648
The basic principle of a distinct idea to reduce an aerodynamic mixing loss induced by the difference in tangential velocity between mainstream flow and rotor shroud leakage flow is presented in "Part I -- Design Concept and Typical Performance of a Swirl Breaker". When the swirl breaker is installed in the circulating region of leakage flow at the rotor shroud exit cavity, the axial distance between the swirl breaker and rotor shroud is a crucial factor to trap the leakage flow into the swirl breaker cavity. In Part II, five cases of geometry with different axial distances between the swirl breaker and rotor shroud, which covered a range for the stage axial distance of actual high and intermediate pressure (HIP) steam turbines, were investigated using an single-rotor computational fluid dynamics (CFD) analysis and verification tests in a 1.5-stage air model turbine. By decreasing the axial distance between the swirl breaker and rotor shroud, the tangential velocity and the mixing region in the tip side which is influenced by the rotor shroud leakage flow were decreased and the stage efficiency was increased. The case of the shortest axial distance between the swirl breaker and rotor shroud increased turbine stage efficiency by 0.7% compared to the conventional cavity geometry. In addition, the measured maximum pressure fluctuation in the swirl breaker cavity was only 0.7% of the entire flow pressure. Consequently, both performance characteristics and structural reliability of swirl breaker were verified for application to real steam turbines.
TOPICS: Rotors, Steam turbines, Leakage flows, Cavities, Pressure, Flow (Dynamics), Computational fluid dynamics, Geometry, Turbines, Design, Reliability, Performance characterization
Andrew Corber, Nader Rizk and Wajid A. Chishty
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041649
The National Jet Fuel Combustion Program (NJFCP) is an initiative being led by the Office of Environment & Energy at the FAA, to streamline the ASTM certification process for alternative aviation fuels. To achieve this objective, the program has identified specific applied research tasks in several areas. The National Research Council of Canada (NRC) is contributing to the NJFCP in the areas of sprays and atomization and high altitude engine performance. This paper describes work pertaining to atomization tests using a reference injection system which involves characterization of the nozzle, comparison of sprays and atomization quality of various conventional and alternative fuels, and the use of the experimental data to validate spray correlations. The paper also briefly explores the viability of a new spray diagnostic system that has potential to reduce test time in characterizing sprays. Measurements were made from ambient up to 10 bar pressures in NRC's High Pressure Spray Facility using optical diagnostics including laser diffraction, phase Doppler anemometry (PDA), LIF/Mie Imaging and laser sheet imaging to assess differences in the atomization characteristics of the test fuels. A total of nine test fluids including six NJFCP fuels and three calibration fluids were used. The experimental data was then used to validate semi-empirical models, developed through years of experience by engine OEMs and modified under the NJFCP, for predicting droplet size and distribution. The work offers effective tools for developing advanced fuel injectors, and generating data that can be used to significantly enhance multi-dimensional combustor simulations.
TOPICS: Fuels, Sprays, Aviation, Imaging, Fluids, Lasers, Engines, Simulation, Jet fuels, Drops, High pressure (Physics), Combustion chambers, Engineering simulation, Nozzles, Diffraction, Combustion, ASTM International, Calibration, Fuel injectors
David Holst, Benjamin Church, Georgios Pechlivanoglou, Ergin Tüzüner, Joseph Saverin, Christian Navid Nayeri and Christian Oliver Paschereit
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041651
Wind turbine industry has a special need for accurate post stall airfoil data. While literature often covers incidence ranges [-10deg;+25deg] smaller machines experience a range of up to 90 deg for horizontal axis and up to 360 deg for vertical axis wind turbines (VAWTs). The post stall data of airfoils is crucial to improve the prediction of the start-up behavior as well as the performance at low tip speed ratios. The present paper analyzes and discusses the performance of the symmetrical NACA 0021 airfoil at three Reynolds numbers (Re = 100k, 140k, and 180k) through 180 deg incidence. The typical problem of blockage within a wind tunnel was avoided using an open test section. The experiments were conducted in terms of surface pressure distribution over the airfoil for a tripped and a baseline configuration. The pressure was used to gain lift, pressure drag, moment data. Further investigations with positive and negative pitching revealed a second hysteresis loop in the deep post stall region resulting in a difference of 0.2 in moment coefficient and 0.5 in lift.
TOPICS: Reynolds number, Experimental analysis, Wind turbines, Airfoils, Vertical axis wind turbines, Pressure, Machinery, Symmetry (Physics), Form drag, Wind tunnels
Takanori Shibata, Hisataka Fukushima and Kiyoshi Segawa
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041650
In high and intermediate pressure (HIP) steam turbines with shrouded blades, it is well known that shroud leakage losses contribute significantly to overall losses. Shroud leakage flow with a large tangential velocity creates a significant aerodynamic loss due to mixing with the mainstream flow. In order to reduce this mixing loss, two distinct ideas for rotor shroud exit cavity geometries were investigated using computational fluid dynamics (CFD) analyses and experimental tests. One idea was an axial fin placed from the shroud downstream casing to reduce the axial cavity gap, and the other was a swirl breaker placed in the rotor shroud exit cavity to reduce the tangential velocity of the leakage flow. In addition to the conventional cavity geometry, three types of shroud exit cavity geometries were designed, manufactured and tested using a 1.5-stage air model turbine with medium aspect ratio blading. Test results showed that the axial fin and the swirl breaker raised turbine stage efficiency by 0.2% and 0.7%, respectively. The proposed swirl breaker was judged to be an effective way to achieve highly efficient steam turbines because it not only reduces the mixing losses but also improves the incidence angle distribution onto the downstream blade row. This study is presented in two papers. The basic design concept and typical performance of the proposed swirl breaker are presented in this Part I, and the effect of axial distance between a swirl breaker and rotor shroud on efficiency improvement is discussed in Part II [8].
TOPICS: Design, Rotors, Steam turbines, Leakage flows, Cavities, Turbines, Blades, Computational fluid dynamics, Leakage, Geometry, Pressure, Flow (Dynamics)
Shuai Guo, Camilo F. Silva, Abdulla Ghani and Wolfgang Polifke
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041652
Thermoacoustic behavior of a combustion system can be determined numerically via acoustic tools coupled with a model for the flame dynamic response. Within such a framework, the flame dynamics can be described by a Finite Impulse Response (FIR) model, which can be derived from LES time series via system identification. However, the estimated FIR model will inevitably contain uncertainties due to low signal-to-noise ratio or finite length of time series. Thus, a necessary step towards reliable thermoacoustic stability analysis is to quantify the impact of uncertainties in FIR model on the growth rate of thermoacoustic modes. There are two practical considerations involved in this topic. First, how to efficiently propagate uncertainties from the FIR model to the modal growth rate of the system, considering it is a high dimensional uncertainty quantification (UQ) problem? Second, since longer CFD simulation time generally leads to less uncertain FIR model identification, how to determine the length of the CFD simulation required to obtain satisfactory confidence? To address these two issues, a dimensional reduction UQ methodology called "Active Subspace'' is employed in the present study. For the first question, Active Subspace is applied to exploit a low-dimensional approximation of the original system, which allows accelerated UQ analysis. Good agreement with Monte Carlo analysis demonstrates the accuracy of the method. For the second question, a procedure based on Active Subspace is proposed, which can serve as an indicator for terminating CFD simulation. The effectiveness of the procedure is verified in the paper.
TOPICS: Stability, Impulse (Physics), Flames, Uncertainty, Uncertainty quantification, Computational fluid dynamics, Simulation, Time series, Dynamics (Mechanics), Signal to noise ratio, Acoustics, Approximation, Dynamic response, Combustion systems
Nesredin Kedir, Calvin Faucett, Luis Sanchez and Sung R Choi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041657
The response of a SiC fibrous ceramic composite to foreign object damage was determined at ambient temperature and velocities ranging from 40 to 150 m/s. Target specimens were impacted, at a normal incidence angle and in a partially supported configuration, using 1.59 mm-diameter hardened steel ball projectiles. Qualitative analysis of the damage morphologies of targets and projectiles were made via scanning electron microscopy (SEM). In addition, the extent of impact damage was characterized by determining the post-impact strength of each target specimen as a function of impact velocity. Relative to the as-received strength, the fibrous composite showed limited strength degradation due to impact with the maximum reduction of 17 % occurring at 150 m/s. A quasi-static analysis of the impact force prediction was also made based on the principle of energy conservation and the results were verified via experimental data.
TOPICS: Ceramic composites, Damage, Projectiles, Temperature, Fiber reinforced composites, Energy conservation, Scanning electron microscopy, Martensitic steel
Mengying Shu, Mingyang Yang, Ricardo F. Martinez-Botas, Kangyao Deng and Lei Shi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041658
The flow in intake manifold of a heavily downsized internal combustion engine has increased levels of unsteadiness due to the reduction of cylinder number and manifold arrangement. The turbocharger compressor is thus exposed to significant pulsating backpressure. This paper studies the response of a centrifugal compressor to this unsteadiness using an experimentally validated numerical method. A CFD model with the volute and impeller is established and validated by experimental measurements. Following this, an unsteady three-dimensional simulation is conducted on a single passage imposed by the pulsating backpressure conditions which are obtained by 1-D unsteady simulation. The performance of the rotor passage deviates from the steady performance and a hysteresis loop, which encapsulates the steady condition, is formed. Moreover, the unsteadiness of the impeller performance is enhanced as the mass flow rate reduces. The pulsating performance and flow structures near stall are more favorable than those seen at constant backpressure. The flow behavior at points with the same instantaneous mass flow rate are substantially different at different time locations on the pulse. The flow in the impeller is determined by not only the instantaneous boundary condition but also by the evolution history of flow field. This study provides insights in the influence of pulsating backpressure on compressor performance in actual engine situations, from which better turbo-engine matching might be benefited.
TOPICS: Impellers, Compressors, Flow (Dynamics), Engines, Simulation, Turbochargers, Computational fluid dynamics, Internal combustion engines, Numerical analysis, Rotors, Boundary-value problems, Cylinders, Manifolds, Intake manifolds
S. Mehrdad Pourkiaee and Stefano Zucca
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041653
A new reduced order modeling technique for nonlinear vibration analysis of mistuned bladed disks with shrouds is presented. The developed reduction technique employs two component mode synthesis methods, namely, the Craig-Bampton (CB) method followed by a modal synthesis based on loaded interface modeshapes (Benfield and Hruda). In the new formulation the fundamental sector is divided into blade and disk components. The CB method is applied to the blade, where nodes lying on shroud contact surfaces and blade-disk interfaces are retained as master nodes, while modal reductions is performed on the disk sector with loaded interfaces. The use of loaded interface component modes allows removing the blade-disk interface nodes from the set of master nodes retained in the reduced model. The result is a much more reduced order model with no need to apply any secondary reduction. In the paper it is shown that the reduced order model of the mistuned bladed disk can be obtained with only single-sector calculation, so that the full finite element model of the entire bladed disk is not necessary. Furthermore, with the described approach it is possible to introduce the blade frequency mistuning directly into the reduced model. The nonlinear forced response is computed using the harmonic balance method (HBM) and alternating frequency/time domain (AFT) approach. Numerical simulations revealed the accuracy, efficiency and reliability of the new developed technique for nonlinear vibration analysis of mistuned bladed disks with shroud friction contacts.
TOPICS: Friction, Disks, Nonlinear dynamics, Blades, Nonlinear vibration, Finite element model, Computer simulation, Reliability, Modeling
Olivier E. Mathieu, Clayton Mulvihill, Henry Curran and Eric Petersen
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041659
ABSTRACT One method frequently used to reduce NOx emissions is exhaust gas recirculation (EGR), where a portion of the exhaust gases, including NOx, is reintroduced into the combustion chamber. While a significant amount of research has been performed to understand the important fuel/NOx chemistry, more work is still necessary to improve the current understanding on this chemistry and to refine detailed kinetics models. To validate models beyond global kinetics data such as ignition delay time or flame speed, the formation of H2O was recorded using a laser absorption diagnostic during the oxidation of a mixture representing a simplistic natural gas (90% CH4 /10% C2H6 (mol.)). This mixture was studied at a fuel lean condition (equiv. ratio = 0.5) and at atmospheric pressure. Unlike in conventional fuel-air experiments, NO2 was used as the oxidant to better elucidate the important, fundamental chemical kinetics by exaggerating the interaction between NOx and hydrocarbon-based species. Results showed a peculiar water formation profile, compared to a former study performed in similar conditions with O2 as oxidant. In the presence of NO2, the formation of water occurs almost immediately before it reaches more or less rapidly (depending on the temperature) a plateau. Modern, detailed kinetics models predict the data with fair to good accuracy overall, while the GRI 3.0 mechanism is proven inadequate for reproducing CH4/C2H6 and NO2 interactions.
TOPICS: Shock (Mechanics), Methane, Model validation, Water, Nitrogen oxides, Fuels, Exhaust gas recirculation, Chemistry, Exhaust systems, Flames, oxidation, Emissions, Ignition delay, Absorption, Combustion chambers, Natural gas, Temperature, Chemical kinetics, Gases, Atmospheric pressure, Lasers

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