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research-article  
Yintong Liu, Liguang Li, Haifeng Lu, Stephan Schmitt, Jun Deng and Lidong Rao
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041516
Homogeneous charge compression ignition (HCCI) is a feasible combustion mode meeting future stringent emissions regulations, and has high efficiency and low NOX and particle emissions. As the narrow working condition range is the main challenge limiting the industrialization of HCCI, combustion mode switching between SI and HCCI is necessary when employing HCCI in mass production engines. Based on a modified production GDI engine equipped with Dual UniValve System (a fully continuously variable valvetrain system), SI/HCCI mode switching under low load condition is investigated. According to the results, combustion mode switching from SI to HCCI is more complicated than from HCCI to SI. As HCCI requires strict boundary conditions for reliable and repeatable fuel auto-ignition, abnormal combustion easily appears in transition cycle, especially when combustion switches from SI to HCCI. Timing control strategies can optimize the combustion of transition cycles. With the optimization of timing control, the mode switching from SI to HCCI can be completed with only 2 transition cycles of late combustion, and abnormal combustion can be avoided during the mode switching from HCCI to SI. Under the low load condition, the indicated efficiency reaches 39% and specific NOX emissions drop down to around 1 mg/L/s when the combustion mode is switched to HCCI mode. Compared to SI mode, the indicated efficiency is increased by 10% and the specific NOX emissions are reduced by around 85%.
TOPICS: Optimization, Homogeneous charge compression ignition engines, Direct injection spark ignition engines, Combustion, Cycles, Emissions, Nitrogen oxides, Stress, Ignition, Switches, Boundary-value problems, Air pollution control, Mass production, Particulate matter, Fuels, Engines
research-article  
Yasuhiro Yoshida, Takuya Yoshida, Yuki Enomoto, Nobuhiro Osaki, Yoshito Nagahama and Yoshifumi Tsuge
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041521
Requirements for the start-up operations of gas turbine combined cycle power plants have become more diverse and now include such items as reduced start-up time, life consumption and fuel gas consumption. In this paper, an optimization method is developed to solve these multi-objective problems. The method obtains optimized start-up curves by iterating the search for the optimal combination of the start-up parameter values and the evaluation of multiple objective functions. The start-up curves generated by this method were found to converge near the Pareto-front representing the best trade-off between the fuel gas consumption of the gas turbine and thermal stress in the steam turbine rotor which are defined as the objective functions. To demonstrate the effectiveness of the developed method, field tests were performed in a commercial power plant. As a result, the fuel gas consumption of HOT start-up was reduced by 22.8% compared with the past operation data. From this result, the developed method was shown to be capable of optimizing the start-up process for gas turbine combined cycle power plants.
TOPICS: Optimization, Power stations, Combined cycle power stations, Gas turbines, Gaseous fuels, Thermal stresses, Rotors, Steam turbines, Tradeoffs
research-article  
Bugra Ertas and Adolfo Delgado
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041520
The following work advances a new concept for a hermetically sealed squeeze film damper (HSFD), which does not require an open-flow lubrication system. The HSFD concept utilizes a submersed plunger within a contained fluidic cavity filled with incompressible fluid and carefully controlled end plate clearances to generate high levels of viscous damping. Although the application space for a HSFD can be envisioned to be quite broad, the context here targets the use of this device as a rotordynamic bearing support damper in compliant gas bearing systems. The effort focused on identifying the HSFD stiffness and damping while varying parameters such as excitation frequency, vibration amplitude, and end plate clearance. Key dynamic pressure measurements in the damper land were used for identifying the onset conditions for film cavitation. The HSFD performance is compared to existing gas bearing support dampers and a conventional open-flow squeeze film dampers (SFD) used in turbomachinery. The damper concept yields high viscous damping coefficients an order of magnitude larger than existing oil-free bearing supports dampers and shows comparable damping levels to current state of the art open-flow SFD. The force coefficients were shown to contribute frequency dependent force coefficients while exhibiting amplitude independent behavior within operating regimes without cavitation. Finally, using experimentally based force density calculations the data revealed threshold cavitation velocities, approximated for the three end seal clearance cases. To complement the experimental work, a Reynolds based fluid flow model was developed and is compared to the HSFD damping and stiffness results.
TOPICS: Dampers, Damping, Flow (Dynamics), Cavitation, Clearances (Engineering), Bearings, Gas bearings, Stiffness, Turbomachinery, Excitation, Incompressible fluids, Pressure measurement, Industrial lubrication systems, Density, Fluid dynamics, Vibration, Cavities
research-article  
Julius Wilhelm, Corina Schwitzke, Hans-Jörg Bauer and Tue Nguyen
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041515
In the present paper an approach for scaling the aerodynamics of advanced seals is presented. Modern advanced seals, such as a self-adaptive gas lubricated face seal comprise elements that are commonly used in turbomachinery sealing. These are labyrinth seals and mechanical face seals. Parameters in?uencing the aerodynamical and mechanical behavior of each seals type are known. However, a combined methodology to scale the aerodynamics of the self-adaptive seal which consists of more than one element has not yet been published. The proposed methodology is applied to a model self-adaptive seal and numerical simulations are performed to prove the validity of the approach. The new methodology ensures the transferability of experimental results at lab scale to engine conditions. Since the new approach allows scaling of self-adaptive seal tests, a new unique test rig will be designed accordingly.
TOPICS: Aerodynamics, Seals, Computer simulation, Engines, Sealing (Process), Mechanical behavior, Turbomachinery
research-article  
Arthur Degeneve, Paul Jourdaine, Clement Mirat, Jean Caudal, Ronan Vicquelin and Thierry Schuller
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041518
Impact of the diverging cup angle of a swirling injector on the flow pattern and stabilization of technically premixed flames is investigated both theoretically and experimentally with the help of OH* chemiluminescence, OH laser induced fluorescence and particle image velocimetry measurements. Recirculation enhancement with a lower position of the internal recirculation zone and a flame leading edge protruding further upstream in the swirled flow are observed as the injector nozzle cup angle is increased. A theoretical analysis is carried out to examine whether this could be explained by changes of the swirl level as the diffuser cup angle is varied. Expressions for changes of the swirl level through a diffuser are derived. It is demonstrated that changes of the swirl level including or not the pressure contribution are not at the origin of the changes observed of the flow and flame patterns in the experiments. The swirl number without the pressure term is then determined experimentally with Laser Doppler velocimetry measurements for a set of diffusers with increasing quarl angles under non-reacting conditions. It is finally shown that the decline of axial velocity and the rise of adverse axial pressure gradient, both due to the cross section area change through the diffuser cup, are the dominant effects that control the leading edge position of the internal recirculation zone. This observation in turn is used to develop a model for the change of this position as the quarl angle varies that shows very good agreement with experiments.
TOPICS: Flow (Dynamics), Flames, Topology, Diffusers, Ejectors, Pressure, Fluorescence, Nozzles, Lasers, Particulate matter, Chemiluminescence, Laser Doppler anemometry, Pressure gradient, Swirling flow, Theoretical analysis
research-article  
David Marten, Matthew Lennie, Georgios Pechlivanoglou, Christian Oliver Paschereit, Alessandro Bianchini, Giovanni Ferrara and Lorenzo Ferrari
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041519
After almost 20 years of absence from research agendas, interest in the vertical axis wind turbine (VAWT) technology is presently increasing again, after the research stalled in the mid 90's in favour of horizontal axis turbines (HAWTs). However, due to the lack of research in past years, there are a significantly lower number of design and certification tools available, many of which are underdeveloped if compared to the corresponding tools for HAWTs. To partially fulfil this gap, a structural FEA model, based on the Open Source multiphysics library PROJECT::CHRONO, was recently integrated with the Lifting Line Free Vortex Wake method inside the Open Source wind turbine simulation code QBlade and validated against numerical and experimental data of the SANDIA 34m rotor. In this work some details about the newly implemented nonlinear structural model and its coupling to the aerodynamic solver are first given. Then, in a continuous effort to assess its accuracy, the code capabilities were here tested on a small scale, fast-spinning (up to 450 rpm) VAWT. After the code validation, an aero-elastically coupled simulation of a rotor self-start has been performed to demonstrate the capabilities of the newly developed model to predict the highly nonlinear transient aerodynamic and structural rotor response.
TOPICS: Simulation, Vertical axis wind turbines, Rotors, Horizontal axis wind turbines, Spinning (Textile), Turbines, Vortices, Wind turbines, Spin (Aerodynamics), Transients (Dynamics), Wakes, Design, Finite element analysis
research-article  
Martin Berthold, Herve P. Morvan, Richard J Jefferson-Loveday, Colin Young, Benjamin C Rothwell and Stephen Ambrose
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041517
High loads and bearing life requirements make journal bearings a potential choice for use in high power, epicyclic gearboxes in jet engines. Computational Fluid Dynamics (CFD) simulations using the Volume of Fluid (VoF) method are carried out in ANSYS Fluent to model the two-phase flow behavior of the oil exiting the bearing and merging into the air surrounding the bearing. This paper presents an investigation of two numerical schemes that are available in ANSYS Fluent to track or capture the air-oil phase interface. Both numerical schemes are used to model the oil outflow behavior of a simplified, concentric journal bearing model. A comparison of both schemes is presented with regards to the accuracy of the phase interface reconstruction and the time required to reach steady state flow field conditions. The CFD predictions are validated against existing literature data with respect to the flow regime, the direction of the predicted oil flow path and the oil film thickness. Based on the findings and considerations of industrial requirements, a recommendation is made for the most suitable scheme to be used. In a representative, eccentric journal bearing the outflow behavior can be expected to be very different. The inlet boundary conditions for the oil emerging into the external journal bearing environment must be consistent with the outlet conditions from the bearing. The second part of this paper therefore focuses on providing a method to generate appropriate inlet boundary conditions for external oil flow from an eccentric journal bearing.
TOPICS: Flow (Dynamics), Computational fluid dynamics, Modeling, Journal bearings, Bearings, Phase interfaces, Outflow, Boundary-value problems, Film thickness, Jet engines, Steady state, Two-phase flow, Engineering simulation, Fluids, Simulation, Stress
research-article  
David Spura, Gunter Eschmann, Wieland Uffrecht and Uwe Gampe
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041452
This paper presents the first experimental results of the systematic investigation of forced convection heat transfer in scaled generic models of steam turbine casing side spaces with varied geometric dimensions under fully turbulent air flow. Data were obtained by two redundant low-heat measuring methods. The results from the steady-state inverse method are in good agreement with the data from the local overtemperature method, which was applied via a novel miniaturized heat transfer coefficient (HTC) sensor concept. All experiments were conducted at the new Side Space Test Rig "SiSTeR" at TU Dresden. The dependencies of the HTC distributions on the axial widths of the cavity and its inlet and on the eccentricity between them were investigated for Reynolds numbers from Re=40,000 to 115,000 in the annular main flow passage. The measured HTC distributions showed a maximum at the stagnation point where the induced jet impinges on the wall surface, and decreasing values towards the cavity corners. Local values scaled roughly with the main flow Reynolds number. The HTC distributions thereby differed considerably depending on the dimensions and the form of the cavity, ranging from symmetric T-shape to asymmetric L-shape, with upstream or downstream shifted sidewalls.
TOPICS: Heat transfer, Cavities, Steam turbines, Shapes, Dimensions, Flow (Dynamics), Reynolds number, Space, Corners (Structural elements), Forced convection, Heat, Sensors, Turbulence, Air flow, Steady state, Heat transfer coefficients
research-article  
Franziska Eichner and Joachim Belz
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041453
Forced response is the main reason for high cycle fatigue in turbomachinery. Not all resonance points in the operating range can be avoided especially for low order excitation. For highly flexible CFRP fans an accurate calculation of vibration amplitudes is required. Forced response analyses were performed for blade row interaction and boundary layer ingestion. The resonance points considered were identified in the Campbell diagram. Forced response amplitudes were calculated using a modal approach and results are compared to the widely used energy method. For the unsteady simulations a time-linearised URANS method was applied. If only the resonant mode was considered the forced response amplitude from the modal approach was confirmed with the energy method. Thereby forced response due to BLI showed higher vibration amplitudes than for blade row interaction. The impact of modes which are not in resonant to the total deformation were investigated by using the modal approach, which so far, only considers one excitation order. A doubling of vibrational amplitude was shown in the case of blade row interaction for higher rotational speeds. The first and third modeshape as well as modes with similar natural frequencies were identified as critical cases. The behaviour in the vicinity of resonance shows high vibration amplitudes over a larger frequency range. This is also valid for high modes with many nodal diameters, which have a greater risk of critical strain.
TOPICS: Blades, Resonance, Vibration, Excitation, Deformation, Simulation, Carbon reinforced plastics, Boundary layers, Engineering simulation, Fans, Turbomachinery, High cycle fatigue, Risk
research-article  
Phillip Ligrani, Zhong Ren, Sneha Vanga, Christopher Allgaier, Federico Liberatore, Rajeshriben Patel, Ram Srinivasan and Shaun Ho
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041451
Experimentally measured results are presented for a test plate with double wall cooling, comprised of full-coverage effusion-cooling on the hot-side of the plate, and cross-flow cooling on the cold-side of the plate. The results presented include the effects of a mainstream pressure gradient. With this arrangement, local blowing ratio decreases significantly with streamwise development along the test section, for every value of initial blowing ratio considered, where this initial value is determined at the most upstream row of effusion holes. Experimental data are given for a sparse effusion hole array. The experimental results are provided for mainstream Reynolds numbers of 92400 to 96600, and from 128400 to 135000, and initial blowing ratios of 3.3-3.6, 4.4, 5.2, 6.1-6.3, and 7.3-7.4. Results illustrate the effects of blowing ratio for the hot-side and the cold-side of the effusion plate. Of particular interest are values of line-averaged film cooling effectiveness and line-averaged heat transfer coefficient, which are generally different for contraction ratio of 4, compared to a contraction ratio of 1, because of different amounts and concentrations of effusion coolant near the test surface. In regard to cold-side measurements on the crossflow side of the effusion plate, line-averaged Nusselt numbers for contraction ratio 4 are often less than values for contraction ratio 1, when compared at the same main flow Reynolds number, initial blowing ratio, and streamwise location.
TOPICS: Flow (Dynamics), Cooling, Pressure gradient, Cross-flow, Reynolds number, Coolants, Film cooling, Heat transfer coefficients
research-article  
Wan-lin Zhao, Guoxiu Li, Lan Wang, Hong-Meng Li, Jie Wang and Shuangyi He
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041386
The control valve is an essential component in electronic unit pump fuel injection systems that controls the flow rate with high precision electrical signal. Thus, high-precision and flexibility are required in the working process of a fuel injection system. The flow capacities (indicated by mass flow rate) of a control valve are important technical indicators in the discharge process of electronic unit pump fuel injection systems. In the present paper, the transient flow characteristics within the control valve during the discharge process of an electronic unit pump have been studied using a CFD approach. Three essential structure parameters of the unit pump control valve (valve core lift, seal diameter and seal cone angle) have been investigated and their effects on circulation characteristics have been evaluated. The variation trends have been observed and the changes of significant physical parameters (i.e. average flow velocity at valve's outlet, vapor volume fraction, and mass flow rate) and the crucial physical field distributions (i.e. velocity field and vapor volume fraction field) were analyzed. Within the investigation, the visualization of the internal flow of control valve provides more detailed information of the flow fields. The paper highlights how each parameter influences flow characteristics and indicates the best parameters to select to enhance the circulation characteristics.
TOPICS: Pumps, Valves, Flow (Dynamics), Fuels, Vapors, Internal flow, Computational fluid dynamics, Visualization, Signals, Unsteady flow
research-article  
Jisu Park and Kyuho Sim
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041384
This study presents a new concept of controllable gas foil bearings (C-GFBs) with piezoelectric actuators. The C-GFB consists of a laminated top foil, bump foil, and piezo stacks and can simply change the bearing shape or film thickness locally and globally by varying the thickness of the piezo stacks with input voltages. The control schemes are 1) clearance control: the bearing clearance adjusted by changing overall piezo stack thickness, and 2) preload control: the mechanical preload modulated by the thickness expansion of several piezo stacks. Bearing lubrication performance is predicted for four cases of C-GFBs with different bearing clearances and preloads. The piezo stack control generates meaningful differences in the fluid-film thickness and pressure. Clearance control has a great effect on the dynamic force coefficients, but preload control slightly increases. Furthermore, the rotordynamic prediction of a rotor supported on two journal C-GFBs is conducted. As a result, both control mode for C-GFB is found to have a positive effect on rotordynamic amplitudes. Finally, using the orbit simulations, the C-GFB is controlled to have a small bearing clearance and large preload at critical speeds to make it possible to stably pass through the critical speeds. Consequently, it turns out that the C-GFB can improve bearing lubrication and rotordynamic performances by controlling only the input voltage of the piezo stacks. In addition, the C-GFB can be used to form various shapes to meet the operation conditions of an applied system.
TOPICS: Piezoelectric materials, Foil bearings, Bearings, Clearances (Engineering), Shapes, Lubrication, Pressure, Simulation, Engineering simulation, Rotors, Film thickness, Fluid films, Piezoelectric actuators
research-article  
Tim S. Rähse, Panagiotis Stathopoulos, Jan-Simon Schäpel, Florian Arnold and Rudibert King
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041387
Constant volume combustion cycles for gas turbines are a very promising alternative to conventional cycles , due to their higher thermal efficiency. Shockless explosion combustion is a method to approximate constant volume combustion. It is a cyclic process consisting of four stages: wave propagation, fuel injection, homogeneous auto-ignition and exhaust. A pressure wave in the combustion chamber facilitates the filling and exhaust phases. During fuel injection, the equivalence ratio is controlled so that the mixture ignition delay time matches its residence time before self ignition. The fuel injected first must have the longest ignition delay time and form the leanest mixture with air. Similarly, fuel injected last forms the richest mixture with air. The total injection time is equal to the time that the wave needs to reach the open combustor end and return as a pressure wave to the closed end. Up to date, fuel stratification has been neglected in thermodynamic simulations of the SEC cycle. The current work presents its effect on the cycle thermal efficiency and the exhaust conditions of shockless explosion combustion chambers. This is done by integrating a fuel injection control algorithm in an existing CFD code. The capability of thisalgorithm to homogenize the auto-ignition process by improving the injection process has been demonstrated in past experimental studies of the SEC. The numerical code used for the simulation of the combustion process is based on the time-resolved 1D-Euler equations with source terms obtained from a detailed chemistry model.
TOPICS: Combustion, Explosions, Fuels, Cycles, Exhaust systems, Ignition, Waves, Combustion chambers, Simulation, Pressure, Ignition delay, Thermal efficiency, Wave propagation, Control algorithms, Computational fluid dynamics, Gas turbines, Chemistry
research-article  
Yoji Okita, Yousuke Mizokami and Jun Hasegawa
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041385
Ceramic matrix composite (CMC) have higher temperature durability and lower density compared to super-alloys. One of promising CMC systems, SiC-SiC is able to sustain its mechanical property at higher temperature, though it inherently needs environmental barrier coating (EBC) to avoid oxidation. There are several requirements for EBC. One of such critical requirements is its resistance to particle erosion, whereas this subject hasn't been well investigated in the past. The present work presents the results of a combined experimental and numerical research to evaluate the erosion characteristics of CMC+EBC material. First, experiments were carried out in an erosion test facility using 50 micron diameter silica as erosion media under typical engine conditions with velocity of 225 m/s, temperature of 1311 K, and impingement angles of 30, 60, and 80deg. The data displayed brittle erosion mode in that the erosion rate increased with impact angles. Also, it was verified that Neilson-Gilchrist erosion model can reproduce the erosion behavior fairly well if the model was properly tuned. The numerical multi-phase simulation with the calibrated erosion model was then applied to compute flow field, particle trajectories, and erosion profile around a generic turbine airfoil to assess the erosion characteristics of the proposed CMC+EBC material when applied to airfoil. The trajectories indicated that the particles primarily impacted the airfoil leading edge and the pressure surface. Surface erosion patterns were predicted based on the calculated trajectories and the experimentally-based erosion characteristics.
TOPICS: Ceramic matrix composites, Erosion, Turbines, Airfoils, Temperature, Particulate matter, Engines, Brittleness, Simulation, Coating processes, Coatings, Alloys, oxidation, Test facilities, Mechanical properties, Durability, Density, Pressure, Flow (Dynamics)
research-article  
Zhigang LI, Zhi FANG and Jun LI
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041313
In order to better understand the leakage and rotordynamic characteristics of the annular gas seal in wet gas conditions, a 3D transient CFD-based perturbation method was proposed for computations of leakage flow rates and rotordynamic force coefficients of annular gas seals with liquid phase in main gas phase, based on inhomogeneous Eulerian-Eulerian multiphase flow model, mesh deformation technique and the multi-frequency rotor whirling orbit model. Numerical results of frequency-dependent rotordynamic force coefficients and leakage flow rates were presented and compared for three types of non-contact annular gas seals, which include a smooth plain annular seal (SPAS), a labyrinth seal (LABY) and a fully-partitioned pocket damper seal (FPDS). These three seals were designed to have the identical rotor diameter, sealing clearance and axial length. The accuracy and availability of the present transient CFD numerical method were demonstrated with the experiment data of leakage flow rates and frequency-dependent rotordynamic force coefficients of the smooth plain seal with four inlet liquid volume fractions (LVF) of 0%, 2%, 5% and 8%. Steady and transient numerical simulations were conducted at inlet air pressure of 62.1 bar, pressure ratio of 0.5, rotational speed of 15 000 rpm and inlet preswirl ratio of 0.3 for four inlet LVFs varying from 0% to 8% and fourteen subsynchronous and synchronous whirling frequencies up to 280 Hz.
TOPICS: Seals, Leakage, Leakage flows, Transients (Dynamics), Pressure, Whirls, Computational fluid dynamics, Rotors, Computation, Dampers, Numerical analysis, Deformation, Clearances (Engineering), Computer simulation, Sealing (Process), Multiphase flow
research-article  
Houchuan Fan, Jimin Ni, Xiuyong Shi, Dayong Qu, Yi Zheng and Yinghong Zheng
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041315
This paper discusses the performance and the mass flow characteristics of a new twin-entry turbocharger turbine with a fixed nozzle entry and a nozzleless entry for automotive application. Because the configuration based on a conventional twin-entry nozzleless turbine has both a fixed nozzle entry and nozzleless entry simultaneously, and the fixed nozzle entry and the nozzleless entry have different turbine incidence angles, stratified flow is formed in the turbine inlet. The numerical simulation results show that the new turbine with double incidence angles has higher efficiency compared to the original twin-entry nozzleless turbine, especially in low-speed condition, which can greatly improve the low-speed torque of engine. By investigating the installation locations of the fixed nozzle, it is beneficial to improve the turbine efficiency when the fixed nozzle is set at the outer scroll near the turbine outlet. The influence of the installation angle on the turbine performances was studied in order to optimize the turbine structure and to find out the rules of the turbine efficiency and mass flow. It shows that 60° is the optimal vane angle. This paper introduces the concept of the double turbine incidence angles and the optimization of the configuration.
TOPICS: Simulation, Turbochargers, Optimization, Turbines, Nozzles, Flow (Dynamics), Computer simulation, Engines, Automotive industry, Torque, Stratified flow
research-article  
Usman Allauddin and Michael Pfitzner
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041308
Recently, a fractal-based algebraic flame surface density (FSD) premixed combustion model has been derived and validated in the context of Large Eddy Simulation (LES). The fractal parameters in the model, namely the cut-off scales and the fractal dimension were derived using theoretical models, experimental and Direct Numerical Simulation (DNS) databases. The model showed good performance in predicting the premixed turbulent flame propagation for low to high Reynold numbers (Re) in ambient as well as elevated pressure conditions. Several LES combustion models have a direct counterpart in the Reynolds-averaged Navier-Stokes (RANS) context. In the present work, a RANS version of the aforementioned LES subgrid scale FSD combustion model is developed. The performance of the RANS model is compared with that of the original LES model and validated with the experimental data. It is found that the RANS version of the model shows similarly good agreement with the experimental data.
TOPICS: Combustion, Turbulence, Density, Flames, Reynolds-averaged Navier–Stokes equations, Algebra, Fractals, Pressure, Computer simulation, Dimensions, Databases, Large eddy simulation
research-article  
Bruce A. Pint, Michael Lance and J. Allen Haynes
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041309
Several factors are being investigated that affect the performance of thermal barrier coatings (TBC) for use in land-based gas turbines where coatings are mainly thermally sprayed. This study examined high velocity oxygen fuel (HVOF), air plasma sprayed (APS) and vacuum plasma sprayed (VPS) MCrAlYHfSi bond coatings with APS YSZ top coatings at 900°-1100°C. For superalloy 247 substrates and VPS coatings tested in 1-h cycles at 1100°C, removing 0.6wt.%Si had no effect on average lifetime in 1-h cycles at 1100°C, but adding 0.3%Ti had a negative effect. Rod specimens were coated with APS, HVOF and HVOF with an outer APS layer bond coating and tested in 100-h cycles in air+10%H2O at 1100°C. With an HVOF bond coating, initial results indicate that 12.5 mm diameter rod specimens have much shorter 100-h cycle lifetimes than disk specimens. Longer lifetimes were obtained when the bond coating had an inner HVOF layer and outer APS layer.
TOPICS: Coatings, Geometry, Cycles, Plasmas (Ionized gases), Gas turbines, Disks, Oxygen, Thermal barrier coatings, Fuels, Vacuum, Superalloys
research-article  
Bugra Ertas and Adolfo Delgado
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041310
The following paper presents a new gas bearing concept that targets machine applications in the megawatt (MW) power range. The concept involves combining a compliant hybrid gas bearing (CHGB) with 2 hermetically sealed squeeze film damper (HSFD) modules installed in the bearing support damper cavities. The main aim of the research was to demonstrate gas bearing-support damping levels using HSFD that rival conventional open-flow squeeze film dampers (SFD) in industry. A detailed description of the bearing design and functionality is discussed while anchoring the concept through a brief recap of past gas bearing concepts. Proof-of-concept experimental testing is presented involving parameter identification of the bearing support force coefficients along with a demonstration of speed and load capability using recessed hydrostatic pads. Lastly, a landing test was performed on the bearing at high speed and load with porous carbon pads to show capability of sustaining rubs at high speeds. The component testing revealed robust viscous damping in the bearing support, which was shown to be comparable to existing state of the art SFD concepts. The damping and stiffness of the system portrayed moderate frequency dependency, which was simulated using a 2D Reynolds based incompressible fluid flow model. Lastly, rotating tests demonstrated the ability of the gas bearing concept to sustain journal excursions and loads indicative of critical speed transitions experienced in large turbomachinery.
TOPICS: Dampers, Gas bearings, Bearings, Damping, Stress, Flow (Dynamics), Testing, Cavities, Hydrostatics, Machinery, Bearing design, Carbon, Incompressible fluids, Stiffness, Turbomachinery
research-article  
Adolfo Delgado and Bugra Ertas
J. Eng. Gas Turbines Power   doi: 10.1115/1.4041311
Ever-increasing demand for cleaner energy is driving the need for higher power density turbomachinery while reducing cost and simplifying design. Gas lubricated bearings, representing one of the enabling technologies that can help maximize these benefits and have been successfully implemented into turbomachinery applications with rotors weights in the order few kg's. However, load capacity and damping limitations of existing gas bearing technologies prevents the development of larger size oil-free drive trains in the MW power output range. Compliantly damped hybrid gas bearings (CHGB) were introduced as an alternative design to overcome these limitations. The CHGB concept addresses damping entitlement through the application of bearing support dampers such a metal mesh. An alternative CHGB design, featuring a novel hermetically seal squeeze film damper (HSFD) in the bearing support, was introduced as alternative approach to metal mesh dampers (MMD) to further improve bearing damping. This paper details the rotordynamic characterization of a CHGB with modular HSFD. Direct and cross-coupled stiffness and damping coefficients are presented for different rotor speeds up to 12,500 rpm, frequencies of excitation between 20-200 Hz, bearing loads between 200-400 lbf, and external hydrostatic pressures reaching 180psi. Direct comparisons to experimental results for a CHGB using (MMD) shows 3X increase in direct damping levels when using HSFD in the compliant bearing support. In addition to the experimental results, an analytical model is presented based on the implementation of the isothermal compressible Reynolds equation coupled to a flexible support.
TOPICS: Bearings, Dampers, Damping, Design, Rotors, Gas bearings, Metals, Stress, Turbomachinery, Power density, Excitation, Hydrostatic pressure, Stiffness, Trains

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