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research-article  
Alejandro Briones, David L Burrus, Joshua P Sykes, Brent Rankin and Andrew W Caswell
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040821
A numerical optimization study is performed on a small-scale high-swirl cavity-stabilized combustor. A parametric geometry is created in CAD software that is coupled with meshing software. The latter automatically transfers meshes and boundary conditions to the solver, which is coupled with a post-processing tool. Steady, incompressible three-dimensional simulations are performed using a multi-phase Realizable k-epsilon Reynolds-averaged Navier-Stokes (RANS) approach with a non-adiabatic flamelet progress variable (FPV) model. There are nine geometrical input parameters. There are five output parameters, viz., pattern factor (PF), RMS of the profile factor deviation, averaged exit temperature, averaged exit swirl angle, and total pressure loss. An iterative design of experiments (DOE) with a recursive Latin Hypercube Sampling (LHS) is performed to filter the most important input parameters. The five major input parameters are found with Spearman's order-rank correlation and R2 coefficient of determination. The five input parameters are used for the adaptive multiple objective (AMO) optimization. This provided a candidate design point with the lowest weighted objective function, which was verified through CFD simulation. The combined filtering and optimization procedures improve the baseline design point in terms of pattern and profile factor. The former halved from that of the baseline design point whereas the latter turned from an outer peak to a center peak profile, closely mimicking an ideal profile. The exit swirl angle favorably increased 25%. The averaged exit temperature and the total pressure losses remained nearly unchanged from the baseline design point.
TOPICS: Combustion chambers, Cavities, Design, Optimization, Simulation, Computer software, Pressure, Temperature, Filtration, Computational fluid dynamics, Computer-aided design, Experimental design, Filters, Geometry, Reynolds-averaged Navier–Stokes equations, Boundary-value problems
research-article  
Zhe Liu, James Braun and Guillermo Paniagua
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040815
Rotating detonation combustors offer theoretically a significant total pressure increase, which may result in enhanced cycle efficiency. The fluctuating exhaust of rotating detonation combustors, however, induces low supersonic flow and large flow angle fluctuations at several kHz which affects the performance of the downstream turbine. In this paper, a numerical methodology is proposed to characterize a supersonic turbine exposed to fluctuations from rotating detonation combustors without any dilution. The inlet conditions of the turbine were extracted from a three dimensional unsteady Reynolds-Averaged Navier-Stokes simulation of a nozzle attached to a rotating detonation combustor, optimized for minimum flow fluctuations and a mass-flow averaged Mach number of 2 at the nozzle outlet. In a first step, a supersonic turbine able to handle steady Mach 2 inflow was designed based on a method of characteristics solver and total pressure loss was assessed. Afterwards unsteady simulations of eight stator passages exposed to periodic oblique shocks were performed. Total pressure loss was evaluated for several oblique shock frequencies and amplitudes. The unsteady stator outlet profile was extracted and used as inlet condition for the unsteady rotor simulations. Finally, a full stage unsteady simulation was performed to characterize the flow field across the entire turbine stage. Power extraction, airfoil base pressure, and total pressure losses were assessed, which enabled the estimation of the loss mechanisms in supersonic turbine exposed to large unsteady inlet conditions.
TOPICS: Explosions, Combustion chambers, Turbines, Pressure, Flow (Dynamics), Simulation, Fluctuations (Physics), Shock (Mechanics), Nozzles, Stators, Supersonic flow, Inflow, Airfoils, Cycles, Exhaust systems, Rotors, Navier-Stokes equations, Mach number
research-article  
Vadim Kloos, Trevor H Speak, Robert J Sellick and Prof.dr. Peter Jeschke
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040822
The more electric aircraft (MEA) concept promises to offer advantages with respect to aircraft performance, maintenance and operating costs. The engines for the MEA concept are based on conventional turbofan architectures. The significantly increased shaft power offtake that is required by the airframe can impair the performance of the engine. In this work, a novel turbofan architecture is investigated for its potential to avoid the problems related to high shaft power offtakes. This architecture is called the dual drive booster because it uses a summation gearbox to drive the booster from both the low- and high-pressure spool. The shaft power, if taken off the booster spool, is effectively provided by both the low- and high-pressure spools. This new concept is benchmarked against a two-spool direct drive and a geared drive turbofan. The presented concept mitigates some of the problems which are encountered during high power offtake in conventional configurations. In particular, the core compressors are less affected by a change in shaft power offtake. This allows higher power offtakes and gives more flexibility during engine design and operation. Additionally, the potential to use the new configuration as a gas turbine-electric hybrid engine is assessed, where electrical power boost is applied during critical flight phases. The ability to convert additional shaft power is compared with conventional configurations. Here, the new configuration also shows superior behavior because the core compressors are significantly less affected by power input than in conventional configurations.
TOPICS: Aircraft, Turbofans, High pressure (Physics), Engines, Compressors, Hybrid engines, Electricity (Physics), Mechanical drives, Maintenance, Architecture, Engine design, Flight, Turbines
research-article  
Matteo Cerutti, Giovanni Riccio, Antonio Andreini, Riccardo Becchi, Dr. Bruno Facchini and Alessio Picchi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040814
A novel dry low-NOx gas turbine technology requires well balanced assessments since the early development phases. The weak knowledge of often conflicting aspects, such as operability and manufacturability, make any roadmap difficult to be drawn. The introduction of innovative manufacturing technologies such as the Direct Metal Laser Sintering (DMLS) process allows rapid manufacturing of components and test them in dedicated facilities to support real-time development of new products. The use of such a manufacturing process allows the adoption of designed experiments based development strategies, which are still uncommon at industrial level, due to the reduced time from drawings to test. The paper describes a reactive test campaign performed by BHGE in cooperation with University of Florence, aimed at the exploration of capabilities of different innovative burners in terms of pollutant emissions containment and blow-out margin. The burner development was supported by CFD investigations with the purpose to have a detailed understating of the flow-field and flame structure and to perform a preliminary screening to select the most promising solutions for the testing phase. The post process of the experimental results has allowed to correlate the main design parameters to burner performance variables discovering possible two-fold optimizations in terms of emissions and operability.
TOPICS: Gas turbines, Natural gas, Nitrogen oxides, Emissions, Manufacturing, Sintering, Engineering drawings, Computational fluid dynamics, Design, Manufacturing technology, Flow (Dynamics), Metals, Lasers, Containment, Testing, Flames, Pollution
research-article  
Chiara Gastaldi and Muzio M. Gola
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040820
This paper furthers recent research by these authors. The starting point is the pre-optimization of solid dampers, which ensures that all dampers bound to misbehave are excluded since the early design stage. The authors now enlarge the scope of their investigations to explore those damper configurations selected inside the admissible design area. The purpose of the paper is to present a set of criteria apt to select a damper configuration which not only avoids unwanted situations, but in addition guarantees high performance under different design conditions. The analysis starts with the definition of a set of requirements a high performance damper should meet. In detail the present investigation seeks to answer the following questions: - in the low excitation regime, what is the frequency shift and the stiffening effect each damper can provide? - for increasing excitation levels, which damper will start slipping sooner? - in the high excitation regime, which damper provides the maximum dissipation? Like pre-optimization, it does not involve nonlinear Finite Element calculations, and unlike existing optimization procedures, is not linked to a specific set of blades the damper may be coupled to. The numerical prediction of the blade-damper coupled dynamics is here used only for validation purposes. The approach on which this paper rests is fully numerical, however real contact parameters are taken from extensive experimental investigations made possible by those purposely developed test rigs which are the distinctive mark of the AERMEC Lab of Politecnico di Torino.
TOPICS: Dampers, Design, Optimization, Excitation, Blades, Finite element analysis, Dynamics (Mechanics), Energy dissipation
research-article  
Vinícius Tavares Silva, Cleverson Bringhenti, Jesuino Takachi Tomita and Olivier Petit
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040770
This work describes a methodology used for counter-rotating propellers performance estimation that was implemented in an in-house program for gas turbine performance prediction, making possible the simulation of the counter-rotating open rotor (CROR) architecture. The methodology was used together with a variable geometry compressor control strategy to avoid surge conditions. Two cases were simulated under transient operation for both fixed and variable geometry compressor. The influence of the variable geometry control on the transient performance of CROR engines was evaluated and a comprehensive understanding on the transient behavior of this type of engine could be obtained. Furthermore, it is possible to conclude that by using variable geometry compressor control the surge margin may be avoided without significant changes in performance, ensuring the safe engine operation.
TOPICS: Engines, Compressors, Transients (Dynamics), Rotors, Geometry, Surges, Propellers, Gas turbines, Simulation
research-article  
Daesik Kim, Seungchai Jung and Heeho Park
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040765
The side-wall cooling liner in a gas turbine combustor serves main purposes-heat transfer and emission control. Additionally, it functions as a passive damper to attenuate thermoacoustic instabilities. The perforations in the liner mainly convert acoustic energy into kinetic energy through vortex shedding at the orifice rims. In previous decades, several analytical and semi-empirical models have been proposed to predict the acoustic damping of the perforated liner. In the current study, a few of the models are considered to embody the transfer matrix method for analyzing the acoustic dissipation in a concentric tube resonator with a perforated element and validated against experimental data in literature. All models are shown to quantitatively-appropriately predict the acoustic behavior under high bias flow velocity conditions. Then, the models are applied to maximize the damping performance in a realistic gas turbine combustor, which is under development. It is found that the ratio of the bias flow Mach number to the porosity can be used as a design guideline in choosing the optimal combination of the number and diameter of perforations in terms of acoustic damping.
TOPICS: Acoustics, Combustion chambers, Design, Gas turbines, Damping, Flow (Dynamics), Mach number, Heat, Cooling, Air pollution control, Dampers, Kinetic energy, Energy dissipation, Porosity, Vortex shedding
research-article  
Max H. Baumgärtner and Thomas Sattelmayer
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040747
Volatile renewable energy sources induce power supply fluctuations. These need to be compensated by flexible conventional power plants. Gas turbines in combined cycle power plants adjust the power output quickly but their turn-down ratio is limited by the slow reaction kinetics which lead to CO emissions. To extend the turn-down ratio, the fuel can be converted to syngas, which exhibits a higher reactivity. By an increasing fraction of syngas in the fuel, the reactivity of the mixture is increased and total fuel mass-flow and the power output can be reduced. An Autothermal On-board Syngas Generator in combination with two burner concepts for natural gas/syngas mixtures was presented in a previous study [1]. The study at hand shows a mass-flow variation of the reforming process and further improvements of the two burner concepts which result in a more application-oriented operation. The first of the two burner concepts comprises a generic swirl stage with a central lance for syngas injection. Syngas is injected swirled and non-swirled. The second concept includes a central swirl stage with an outer ring of jets. For this burner, syngas is injected in both stages. For both burners, combustion performance is analyzed by OH*-chemiluminescence and gaseous emissions. The lowest possible adiabatic flame temperature without a significant increase of CO emissions was 170K - 210K lower for the syngas compared to low load pure natural gas combustion. This corresponds to a decrease of 15 - 20% in terms of thermal power.
TOPICS: Stress, Syngas, Emissions, Fuels, Flow (Dynamics), Combustion, Natural gas, Power stations, Combined cycle power stations, Flames, Generators, Renewable energy sources, Temperature, Chemical kinetics, Thermal energy, Chemiluminescence, Fluctuations (Physics), Jets, Gas turbines
research-article  
Artur Szymański, Włodzimierz Wróblewski, Daniel Frączek, Krzysztof Bochon, Sławomir Dykas and Krzysztof Marugi
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040767
This paper presents the methodology and results of the optimisation of a straight-through labyrinth seal with two inclined fins against smooth-land. The optimisation was performed using commercial tools implemented in the ANSYS environment, such as Goal-Driven Optimization. The response surfaces were created based on Latin hypercube samples found from CFD calculations. The CFD solver, using a steady-state scheme with the k - omega Shear Stress Transport turbulence model, was applied. A screening algorithm was used to find the best candidates on the response surfaces. The objective function adopted in the labyrinth seal optimisation was the minimisation of the discharge coefficient value. A wide range of parameters of the fins position and shape were taken into account, with physically justified degrees of freedom. The optimisation results were supported by the results of an in-house experiment performed on a stationary, linear test rig. The test rig was fed by a high-capacity vacuum air blower, with high-precision hot-wire anemometry mass flow evaluation. The reductions in the leakage significantly exceed the uncertainties of the CFD model and the test rig accuracy. The factors that had the most substantial impact on the leakage reduction were the location, inclination and thickness of the fins. The experimental results were compared with the calculations and the optimisation effects, highlighting some tendencies in the labyrinth seal flow behaviour. Good agreement was obtained between the optimisation results and the experimental data, proving that the presented methodology is sufficient for the labyrinth seal optimisation.
TOPICS: Optimization, Fins, Computational fluid dynamics, Leakage, Flow (Dynamics), Turbulence, Vacuum, Wire, Degrees of freedom, Algorithms, Shapes, Steady state, Discharge coefficient, Uncertainty, Shear stress
research-article  
Felix Figaschewsky, Benjamin Hanschke and Arnold Kühhorn
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040748
The assessment of vibration levels of rotating blades in turbomachinery is a fundamental task. Traditionally, this assessment is done by the application of strain gauges to some blades of the assembly. In contrast to strain gauges, BTT offers a contactless monitoring of all blades of a rotor and there is no need of a telemetry system. A major issue in the interpretation of BTT data is the heavily undersampled nature of the signal. Usually, newly developed BTT algorithms are tested with sample data created by simplified structural models neglecting many of the uncertainties and disturbing influences of real applications. This work focuses on the creation of simulated BTT datasets as close as possible to real case measurements. For this purpose a SNM representation of a compressor rotor is utilized. This model is able to include a large number of features present in real measurements, such as mistuning, static blade deflections due to centrifugal loads, aerodynamic damping and multiple mode resonances. Additionally, manufacturing deviations of the blade geometry, probe positioning errors in the BTT system and noise in the time of arrivals are captured by the BTT simulation environment. The main advantage of the created data is the possibility to steadily increase the signal complexity. This allows the assessment of the influence of different features occurring in real measurements on the performance and accuracy of the analysis algorithms. Finally, a comparison of simulated BTT data and real data acquired from a rig test is shown to validate the presented approach.
TOPICS: Engines, Rotors, Blades, Signals, Strain gages, Algorithms, Manufacturing, Simulation, Stress, Noise (Sound), Damping, Compressors, Telemetry, Turbomachinery, Rotating blades, Uncertainty, Deflection, Errors, Geometry, Probes, Vibration, Resonance
research-article  
Clemens Griebel
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040749
In this paper, different notch and partition wall arrangements of a fully partitioned pocket damper seal (FPDS) are investigated using Computational Fluid Dynamics (CFD). The CFD model is derived for a baseline FPDS design reflecting the full sealing configuration with a structured mesh. Steady-state simulations are performed for eccentric rotor position and different operational parameters. The results are validated using experimental cavity pressure measurements. In transient computations, rotor whirl is modeled as a circular motion around an initial eccentricity using a moving mesh technique. Different whirl frequencies are computed to account for the frequency-dependent behavior of damper seals. The stiffness and damping coefficients are evaluated from the impedances in the frequency domain using a Fast Fourier Transform. The validated model is then transferred to varying designs. In addition to the baseline design, six different notch arrangements with constant clearance ratio were modeled. Moreover, two partition wall design variations were studied based on manufacturability considerations. Predicted leakage as well as frequency-dependent stiffness and damping coefficients are presented and the impact of geometry variations on these parameters is discussed. The results suggest that a single centered notch is favorable and indicate considerably higher effective damping for a design with staggered partition walls. A rounded partition wall design with significantly eased manufacturing reveals good performance.
TOPICS: Computational fluid dynamics, Dampers, Geometry, Leakage, Design, Damping, Stiffness, Whirls, Rotors, Cavities, Computation, Fast Fourier transforms, Steady state, Engineering simulation, Pressure measurement, Manufacturing, Simulation, Sealing (Process), Transients (Dynamics), Clearances (Engineering)
research-article  
Luis San Andrés, Jing Yang and Xueliang Lu
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040766
Subsea pumps and compressors must withstand multi-phase flows whose gas volume fraction (GVF) or liquid volume fraction (LVF) varies over a wide range. Gas or liquid content in the primary stream affects the leakage and rotordynamic performance of secondary flow components, namely seals, thus affecting the process efficiency and mechanical reliability of pumping/compressing systems. This paper, complementing a parallel experimental program, presents a computational fluid dynamics (CFD) analysis to predict the leakage, drag power and rotordynamic coefficients of a smooth annular seal supplied with an air in oil mixture. The CFD seal leakage and drag power decrease steadily as the GVF increases. A multiple-frequency whirl orbit method aids in the calculation of seal rotordynamic coefficients. The injection of air in the oil immediately produces frequency dependent force coefficients; in particular the direct stiffness which hardens with frequency. The effect is most remarkable for small GVFs, as low as 0.2. The predictions of CFD and bulk-flow model (BFM), reproduce the test force coefficients with great fidelity. Incidentally, early engineering practice points out to air injection as a remedy to cure persistent vibration in vertical pumps, submersible and large size hydraulic. Presently, the model predictions, supported by the test data, demonstrate even a small content of gas in the liquid stream significantly raises the seal direct stiffness, thus displacing the system critical speed to safety. The CFD model and a dedicated test rig, predictions and test data complementing each other, enable engineered seals for extreme applications.
TOPICS: Torque, Computational fluid dynamics, Leakage, Pumps, Stiffness, Flow (Dynamics), Drag (Fluid dynamics), Reliability, Multiphase flow, Ocean engineering, Safety, Compressors, Submersibles, Whirls, Vibration
research-article  
Alessandro Orchini, Georg A. Mensah and Jonas P. Moeck
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040768
In this theoretical and numerical analysis, a low-order network model is used to investigate a thermoacoustic system with discrete rotational symmetry. Its geometry resembles that of the MICCA combustor; the FDF employed in the analysis is that of a single-burner configuration, and is taken from experimental data reported in the literature. We show how most of the dynamical features observed in the MICCA experiment, including the so-called slanted mode, can be predicted within this framework, when the interaction between a longitudinal and an azimuthal thermoacoustic mode is considered. We show how these solutions relate to the symmetries contained in the equations that model the system. We also discuss how considering situations in which two modes are linearly unstable compromises the applicability of stability criteria available in the literature.
TOPICS: Stability, Combustion chambers, Numerical analysis, Geometry, Network models
research-article  
S. Reitenbach, A. Krumme, T. Behrendt, M. Schnös, T. Schmidt, S. Hönig, R. Mischke and E. Moerland
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040750
The purpose of this paper is to present a multi-disciplinary pre-design process and its application to three aero engine models. First, a twin spool mixed flow turbofan engine model is created for validation purposes. The second and third engine models investigated comprise future engine concepts: a Counter Rotating Open Rotor and an Ultra High Bypass Turbofan. The turbofan used for validation is based on publicly available reference data from manufacturing and emission certification. At first the identified interfaces and constraints of the entire pre-design process are presented. An important factor of complexity in this highly iterative procedure is the intricate data flow, as well as the extensive amount of data transferred between all involved disciplines and among different fidelity levels applied within the design phases. To cope with the inherent complexity data modeling techniques have been applied to explicitly determine required data structures of those complex systems. The resulting data model characterizing the components of a gas turbine and their relationships in the design process is presented in detail. Based on the data model the entire engine pre-design process is presented. Starting with the definition of a flight mission scenario and resulting top level engine requirements thermodynamic engine performance models are developed. By means of these thermodynamic models, a detailed engine component pre-design is conducted. The aerodynamic and structural design of the engine components are executed using a stepwise increase in level of detail and are continuously evaluated in context of the overall engine system.
TOPICS: Design, Engines, Turbofans, Flow (Dynamics), Structural design, Manufacturing, Aircraft engines, Complex systems, Emissions, Engineering disciplines, Gas turbines, Modeling, Rotors, Flight
research-article  
Tommaso Bacci, Tommaso Lenzi, Alessio Picchi, Lorenzo Mazzei and Dr. Bruno Facchini
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040714
Modern lean burn aero-engine combustors outflows are characterized by aggressive swirl fields, high turbulence intensities and strong hot streaks. In order to understand combustor-turbine interactions, it is mandatory to collect reliable experimental data at representative flow conditions. While the separated effects of temperature, swirl and turbulence on the first turbine stage have been widely investigated, reduced experimental data is available when it comes to consider all these factors together. An annular three-sector combustor simulator with fully cooled high pressure vanes has been installed at the THT Lab of University of Florence. The rig is equipped with three axial swirlers, effusion cooled liners and six film cooled high pressure vanes passages. In order to generate representative conditions, a heated mainstream passes though the axial swirlers of the combustor simulator, while the effusion cooled liners are fed by air at ambient temperature. The resulting flow field exiting from the combustor simulator and approaching the cooled vane can be considered representative of a modern Lean Burn aero engine combustor with swirl angles above ±50°, turbulence intensities up to about 28% and maximum-to-minimum temperature ratio of about 1.25. With the aim of investigating the hot streaks evolution through the cooled high pressure vane, the aerothermal field has been evaluated by means of a five hole probe equipped with a thermocouple and traversed upstream and downstream of the cascade.
TOPICS: Flow (Dynamics), High pressure (Physics), Combustion chambers, Outflow, Turbulence, Temperature, Turbines, Aircraft engines, Probes, Thermocouples, Temperature effects, Cascades (Fluid dynamics)
research-article  
Philippe Dagaut, Yuri Bedjanian, Guillaume Dayma, Fabrice Foucher, Benoit Grosselin, Emmanouil Romanias and Roya Shahla
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040712
The combustion of conventional fuels (Diesel and Jet A-1) with 10-20% vol. oxygenated biofuels (ethanol, 1-butanol, methyl octanoate, rapeseed oil methyl ester, diethyl carbonate, tri(propylene glycol)methyl ether, i.e., CH3(OC3H6)3OH, and 2,5-dimethylfuran) and a synthetic paraffinic kerosene was studied. The experiments were performed using an atmospheric pressure laboratory premixed flame and a four-cylinder four-stroke Diesel engine operating at 1500 rpm. Soot samples from kerosene blends were collected above a premixed flame for analysis. Polyaromatic hydrocarbons (PAHs) were extracted from the soot samples. After fractioning, they were analyzed by high-pressure liquid chromatography (HPLC) with UV and fluorescence detectors. C1 to C8 carbonyl compounds were collected at the Diesel engine exhaust on 2,4-dinitrophenylhydrazine coated cartridges (DNPH) and analyzed by HPLC with UV detection. The data indicated that blending conventional fuels with biofuels has a significant impact on the emission of both carbonyl compounds and PAHs adsorbed on soot. The global concentration of 18 PAHs (1-methyl-naphthalene, 2-methyl-naphthalene, and the 16 US priority EPA PAHs) on soot was considerably lowered using oxygenated fuels, except 2,5-dimethylfuran. Conversely, the total carbonyl emission increased by oxygenated biofuels blending. Among them, ethanol and 1-butanol were found to increase considerably the emissions of carbonyl compounds.
TOPICS: Combustion, Fuels, Biofuel, Pollution, Emissions, Soot, Flames, Ethanol, Diesel engines, Ultraviolet radiation, Fluorescence, High pressure (Physics), Ethers (Class of compounds), Atmospheric pressure, Sensors, Ester, Cylinders, Diesel, Exhaust systems
research-article  
Marius Grübel, Markus Schatz and Damian M. Vogt
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040711
A numerical second law analysis is performed to determine the entropy production due to irreversibilities in condensing steam flows. In the present work the classical approach to calculate entropy production rates in turbulent flows based on velocity and temperature gradients is extended to two-phase condensing flows modeled within an Eulerian-Eulerian framework. This requires some modifications of the general approach and the inclusion of additional models to account for thermodynamic and kinematic relaxation processes. With this approach, the entropy production within each mesh element is obtained. In addition to the quantification of thermodynamic and kinematic wetness losses, a breakdown of aerodynamic losses is possible to allow for a detailed loss analysis. The aerodynamic losses are classified into wake mixing, boundary layer and shock losses. The application of the method is demonstrated by means of the flow through a well known steam turbine cascade test case. Predicted variations of loss coefficients for different operating conditions can be confirmed by experimental observations. For the investigated test cases, the thermodynamic relaxation contributes the most to the total losses and the losses due to droplet inertia are only of minor importance. The variation of the predicted aerodynamic losses for different operating conditions is as expected and demonstrates the suitability of the approach.
TOPICS: Flow (Dynamics), Steam, Entropy, Kinematics, Relaxation (Physics), Steam turbines, Temperature gradient, Inertia (Mechanics), Turbulence, Cascades (Fluid dynamics), Drops, Wakes, Shock (Mechanics), Boundary layers
research-article  
Bernd Beirow, Arnold Kühhorn, Felix Figaschewsky, Alfons Bornhorn and Oleg V. Repetckii
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040715
The effect of intentional mistuning has been analyzed for an axial turbocharger blisk with the objective of limiting the forced response due to low engine order excitation (LEO). The idea behind the approach was to increase the aerodynamic damping for the most critical fundamental mode in a way that a safe operation is ensured without severely losing aerodynamic performance. Apart from alternate mistuning a more effective mistuning pattern is investigated, which has been derived by means of optimization employing genetic algorithms. In order to keep the manufacturing effort as small as possible only two blade different geometries have been allowed which means that an integer optimization problem has been formulated. Two blisk prototypes have been manufactured for the purpose of demonstrating the benefit of the intentional mistuning pattern identified in this way: A first one with and a second one without employing intentional mistuning. The real mistuning of the prototypes has been experimentally identified. It is shown that the benefit regarding the forced response reduction is retained in spite of the negative impact of unavoidable additional mistuning due to the manufacturing process. Independently, further analyzes have been focused on the robustness of the solution by considering increasing random structural mistuning and aerodynamic mistuning as well. The latter one has been modeled by means of varying aerodynamic influence coefficients (AIC) as part of Monte Carlo simulations. Reduced order models have been employed for these purposes.
TOPICS: Engines, Manufacturing, Simulation, Turbochargers, Engineering prototypes, Damping, Engineering simulation, Optimization, Blades, Genetic algorithms, Robustness, Excitation
research-article  
David Gonzalez Cuadrado, Francisco Lozano, Valeria Andreoli and Guillermo Paniagua
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040713
In this paper, we propose a two-step methodology to evaluate the convective heat flux along the rotor casing using an engine-scalable approach based on Discrete Green's Functions. The first step consists in the use of an inverse heat transfer technique to retrieve the heat flux distribution on the shroud inner wall by measuring the temperature of the outside wall; the second step is the calculation of the convective heat flux at engine conditions, using the experimental heat flux and the Green Functions engine-scalable technique. Inverse methodologies allow the determination of boundary conditions, in this case the inner casing surface heat flux, based on measurements from outside of the system, which prevents aerothermal distortion caused by routing the instrumentation into the test article. The heat flux, retrieved from the inverse heat transfer methodology, is related to the rotor tip gap. Therefore, for a given geometry and tip gap, the pressure and temperature can also be retrieved. In this work, the Digital Filter Method is applied in order to take advantage of the response of the temperature to heat flux pulses. The Discrete Green's Function approach employs a matrix to relate an arbitrary temperature distribution to a series of pulses of heat flux. In the present procedure, the terms of the Green's Function matrix are evaluated with the output of the inverse heat transfer method. Given that key dimensionless numbers are conserved, the Green's Functions matrix can be extrapolated to engine-like conditions.
TOPICS: Heat transfer, Engines, Rotors, Heat flux, Temperature, Pressure, Dimensionless numbers, Boundary-value problems, Filters, Geometry, Temperature distribution, Exterior walls, Instrumentation
research-article  
Dennis Toebben, Adrian Hellmig, Piotr Luczynski, Manfred Wirsum, Wolfgang F. D. Mohr and Klaus Helbig
J. Eng. Gas Turbines Power   doi: 10.1115/1.4040717
Due to the growing share of volatile renewable power generation, conventional power plants with a high flexibility are required. This leads to high thermal stresses inside the heavy components which reduces the lifetime. To improve the ability for fast start-ups, information about the metal temperature inside the rotor and the casing are crucial. Thus, an efficient calculation approach is required which enables the prediction of the temperature distribution in a whole multistage steam turbine. The present paper deals with the theoretical investigation of steam turbine warm-keeping operation with hot air. This operation is totally different from the conventional operation conditions, due to the different working fluid with low mass flow rates and a slow rotation. Based on quasi-steady transient multistage CHT simulations, an analytical heat transfer correlation has been developed, since, the commonly known calculation approaches from literature are not suitable for this case. The presented heat transfer correlations describe the convective heat transfer separately at vane and blade as well as the seal surfaces. The correlations are based on a CHT model of three repetitive steam turbine stages. The simulations show a similar behavior of the Nusselt-number in consecutive stages. Hence, the developed area related heat transfer correlations are independent of the position of the stage. Finally, the correlations are implemented into a solid body Finite-Element model and compared to the fluid-dynamic simulations.
TOPICS: Heat transfer, Steam turbines, Engineering simulation, Simulation, Fluids, Metals, Rotation, Flow (Dynamics), Temperature, Thermal stresses, Transients (Dynamics), Convection, Power stations, Rotors, Blades, Finite element model, Renewable energy, Temperature distribution

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