bluuebunny/crossref_metadata_2025 huggingface dataset:
Aeroengine Gas Path Performance Parameter Prediction Based on GM(1,1) Rolling-Markov Chain Approach
Authors: Zhao Ningbo , Yang Jialong , Li Shuying
Published: August 2015

As one of the most important gas path performance parameters, the exhaust gas temperature (EGT) can provide more effective information about the health state of aeroengine. However, the changing process of aeroengine EGT is often affected by many uncertain factors and the sample data are relatively less, which make it difficult to predict its trend accurately by the traditional regression analysis method. Aiming at this problem, the GM(1,1) rolling-Markov chain model is proposed and used for aeroengine EGT prediction in this paper. Based on the equal dimensional new information theory, GM(1,1) rolling model is utilized to predict the changing trend of aeroengine EGT firstly. Then the Markov chain theory is used to solve the influence of random fluctuation on prediction accuracy, which can achieve an effective estimate of the non-linear parameter. As an example, the historical monitoring data of EGT from one aeroengine of Air China is used to verify the prediction performance of GM(1,1) rolling-Markov chain model. The analysis results show that this model has higher prediction accuracy and can effectively reflect the random fluctuation characteristics of EGT, which provides a new method for aeroengine gas path performance parameter prediction.
Ambient Temperature Impact on Pressurized SOFC Hybrid Systems
Authors: Larosa Luca , Traverso Alberto , Zaccaria Valentina
Published: August 2015

In this paper advanced control strategies based on Model Predictive Control (MPC) method are compared against a traditional PID controller in a Gas Turbine Pressurized SOFC hybrid system.

A model of the integrated mGT-SOFC hybrid system has been developed to analyze the impact of ambient temperature changes on system performance and dynamic behaviour. Four different MIMO controllers (multi input multi output) based on a linearized system model have been implemented in order to control fuel cell temperature and power with different ambient temperatures. Fuel cell temperature is regulated by manipulating the cell by-pass mass flow, while power is regulated by changing the fuel cell electrical current and fuel mass flow (the fuel utilization factor is kept constant). Load following simulations have been carried out as follows: the same load ramp from 100% to 80% of fuel cell power and back has been set and studied under three different ambient conditions, 263K, 288K and 313K (−10°C, 15°C and 40°C).

MPC demonstrated superior performance over the two distributed PID controls, thanks to the better setpoint tracking on the cell temperature, which is particularly evident when the ambient temperature deviates from the nominal condition. This is mainly explained by the capability of MPC in including the effects of non-linearities of the real system.
Stagnation Region Heat Transfer Augmentation at Very High Turbulence Levels
Authors: Kingery J. E. , Ames F. E.
Published: August 2015

A database for stagnation region heat transfer has been extended to include heat transfer measurements acquired downstream from a new high intensity turbulence generator. This work was motivated by gas turbine industry heat transfer designers who deal with heat transfer environments with increasing Reynolds numbers and very high turbulence levels. The new mock aero-combustor turbulence generator produces turbulence levels which average 17.4%, which is 37% higher than the older turbulence generator. The increased level of turbulence is caused by the reduced contraction ratio from the liner to the exit. Heat transfer measurements were acquired on two large cylindrical leading edge test surfaces having a four to one range in leading edge diameter (40.64 cm and 10.16 cm). Gandvarapu and Ames [1] previously acquired heat transfer measurements for six turbulence conditions including three grid conditions, two lower turbulence aero-combustor conditions, and a low turbulence condition. The data are documented and tabulated for an eight to one range in Reynolds numbers for each test surface with Reynolds numbers ranging from 62,500 to 500,000 for the large leading edge and 15,625 to 125,000 for the smaller leading edge. The data show augmentation levels of up to 136% in the stagnation region for the large leading edge. This heat transfer rate is an increase over the previous aero-combustor turbulence generator which had augmentation levels up to 110%. Note, the rate of increase in heat transfer augmentation decreases for the large cylindrical leading edge inferring only a limited level of turbulence intensification in the stagnation region. The smaller cylindrical leading edge shows more consistency with earlier stagnation region heat transfer results correlated on the TRL (Turbulence, Reynolds number, Length scale) parameter. The downstream regions of both test surfaces continue to accelerate the flow but at a much lower rate than the leading edge. Bypass transition occurs in these regions providing a useful set of data to ground the prediction of transition onset and length over a wide range of Reynolds numbers and turbulence intensity and scales.
Dynamic Behavior of a Solar Hybrid Gas Turbine System
Authors: Felsmann Christian , Gampe Uwe , Freimark Manfred
Published: August 2015

Solar hybrid gas turbine technology has the potential to increase the efficiency of future solar thermal power plants by utilizing solar heat at a much higher temperature level than state of the art plants based on steam turbine cycles. In a previous paper the authors pointed out, that further development steps are required for example in the field of component development and in the investigation of the system dynamics to realize a mature technology for commercial application [1].

In this paper new findings on system dynamics are presented based on the simulation model of a solar hybrid gas turbine with parallel arrangement of the combustion chamber and solar receivers. The operational behavior of the system is described by means of two different scenarios. The System operation in a stand-alone electrical supply network is investigated in the first scenario. Here it is shown that fast load changes in the network lead to a higher shaft speed deviation of the electric generator compared to pure fossil fired systems. In the second scenario a generator load rejection, as a worst case, is analyzed. The results make clear that additional relief concepts like blow-off valves are necessary as the standard gas turbine protection does not meet the specific requirements of the solar hybrid operation. In general the results show, that the solar hybrid operational modes are much more challenging for the gas turbines control and safety system compared to pure fossil fired plants due to the increased volumetric storage capacity of the system.
CCPP Operational Flexibility Extension Below 30% Load Using Reheat Burner Switch-Off Concept
Authors: Therkorn Dirk , Gassner Martin , Lonneux Vincent , Zhang Mengbin , Bernero Stefano
Published: August 2015

Highly competitive and volatile energy markets are currently observed, as resulting from the increased use of intermittent renewable sources. Gas turbine combined cycle power plants (CCPP) owners therefore require reliable, flexible capacity with fast response time to the grid, while being compliant with environmental limitations. In response to these requirements, a new operation concept was developed to extend the operational flexibility by reducing the achievable Minimum Environmental Load (MEL), usually limited by increasing pollutant emissions.

The developed concept exploits the unique feature of the GT24/26 sequential combustion architecture, where low part load operation is only limited by CO emissions produced by the reheat (SEV) burners. A significant reduction of CO below the legal limits in the Low Part Load (LPL) range is thereby achieved by individually switching the SEV burners with a new operation concept that allows to reduce load without needing to significantly reduce both local hot gas temperatures and CCPP efficiency.

Comprehensive assessments of the impact on operation, emissions and lifetime were performed and accompanied by extensive testing with additional validation instrumentation. This has confirmed moderate temperature spreads in the downstream components, which is a benefit of sequential combustion technology due to the high inlet temperature into the SEV combustor. The following commercial implementation in the field has proven a reduction of MEL down to 26% plant load, corresponding to 18% gas turbine load. The extended operation range is emission compliant and provides frequency response capability at high plant efficiency. The experience accumulated over more than one year of successful commercial operation confirms the potential and reliability of the concept, which the customers are exploiting by regularly operating in the LPL range.
Influence of Gas Turbine Exhaust CO2 Concentration on the Performance of Post Combustion Carbon Capture Plant
Authors: Akram Muhammad , Blakey Simon , Pourkashanian Mohamed
Published: August 2015

As a result of increased concern over Greenhouse Gas emissions, capture of CO2 from stationary power sources is a topic under discussion throughout the world. The most developed technology for the application is post combustion carbon capture using liquid solvents. However, due to very low concentration of CO2 in the gas turbine emitted flue gas, energy penalty caused by the capture process is relatively high. One of the methods to increase CO2 concentration is the recycling of flue gas (also termed as EGR) in which part of the flue gas is sent back to join the air stream entering the compressor. This paper presents results of an experimental campaign carried out at the Pilot Scale Advanced Capture Technology (PACT) facilities of the UK Carbon Capture and Storage Research Centre (UKCCSRC). A Turbec T100 microturbine of 100kWe is integrated with a post combustion carbon capture plant of 1TPD (Ton per day) CO2 capture capacity. The microturbine is very lean combustion system and produces a flue gas having only 1.5% CO2. Therefore, in order to simulate EGR on industrial gas turbines which produce around 4–5% CO2 in the exhaust stream, CO2 from a cryogenic storage tank was injected into the slip stream of the gas turbine exhaust. The impact of different CO2 concentrations (representing EGR) on the post combustion carbon capture process is experimentally evaluated. It is observed that the energy penalty caused by the capture process is considerably reduced at higher CO2 concentration in the absorber inlet flue gas stream. EGR also has a negative impact on the produced power from the gas turbine as well as the combustion process. However, it has positive impact on the power output from steam turbine. Optimum recycle ratio for maximum power output from combined cycle gas turbine is discussed. Performance of the absorption column as indicated by rich and lean solvent CO2 loadings is discussed. Moreover, emissions of solvent and some of the degradation products with the exhaust gas from the capture plant are monitored and reported.
Aerothermal Prediction of an Aeronautical Combustion Chamber Based on the Coupling of Large Eddy Simulation, Solid Conduction and Radiation Solvers
Authors: Berger Sandrine , Richard Stéphane , Staffelbach Gabriel , Duchaine Florent , Gicquel Laurent
Published: August 2015

A precise knowledge of the thermal environment is essential for gas turbines design. Combustion chamber walls in particular are subject to strong thermal constraints. It is thus essential for designers to characterize accurately the local thermal state of such devices. Today, the determination of wall temperatures is performed experimentally by complex thermocolor tests. To limit such expensive experiments and integrate the knowledge of the thermal environment earlier in the design process, efforts are currently performed to provide high fidelity numerical tools able to predict the combustion chamber walls temperature. Many coupled physical phenomena are involved: turbulent combustion, convection and mixing of hot products and cold flows, conduction in the solid parts as well as gas to gas, gas to wall and wall to wall radiative transfers. The resolution of such a multiphysics problem jointly in the fluid and the solid domains can be done numerically through the use of several dedicated numerical and algorithmic approaches. In this paper, a partitioned coupling methodology is used to investigate the solid steady state wall temperature of a helicopter combustor in take-off conditions. The methodology relies on a high fidelity Large Eddy Simulation reacting flow solver coupled to conduction and radiative solvers. Different computations are presented in order to assess the role of each heat transfer process in the temperature field. A conjugate heat transfer simulation is first proposed and compared with experimental thermocolor tests. The effect of radiation is then investigated comparing relative importance of convective and radiative heat fluxes.
Investigation of Lean Premixed Swirl-Stabilized Hydrogen Burner With Axial Air Injection Using OH-PLIF Imaging
Authors: Reichel Thoralf G. , Goeckeler Katharina , Paschereit Oliver
Published: August 2015

In the context of lean premixed combustion, the prevention of upstream flame propagation in the premixing zone, referred to as flashback, is a crucial challenge related to the application of hydrogen as a fuel for gas turbines. The location of flame anchoring and its impact on flashback tendencies in a technically premixed, swirl-stabilized hydrogen burner are investigated experimentally at atmospheric pressure conditions using planar laser-induced fluorescence of hydroxyl radicals (OH-PLIF). The inlet conditions are systematically varied with respect to equivalence ratio (ϕ = 0.2–1.0), bulk air velocity u0 = 30–90m/s and burner preheat temperature ranging from 300K to 700K. The burner is mounted in the atmospheric combustion test rig at the HFI, firing at a power of up to 220 kW into a 105 mm diameter quartz cylinder, which provides optical access to the flame region. The experiments were performed using an in-house burner design that previously proved to be highly resistant against flashback occurrence by applying the axial air injection strategy. Axial air injection constitutes a non-swirling air jet on the central axis of the radial swirl generator, thus, influencing the vortex breakdown position. High axial air injection yields excellent flashback resistance and is used to investigate the whole inlet parameter space. In order to trigger flashback, the amount of axially injected air is reduced, which allowed to investigate the near flashback flame behavior. Results show that both, fuel momentum of hydrogen and axial air injection alter the isothermal flow field and cause a downstream shift of the axial flame front location. Such a shift is proven beneficial for flashback resistance. This effect was quantified by applying an edge detection algorithm to the OH-PLIF images, in order to extract the location of maximum flame front likelihood xF. The temperature and equivalence ratio dependence of the parameters xF is identified to be governed by the momentum ratio between fuel and air flow J. These results contribute to the understanding of the superior flashback limits of configurations applying high amounts of axial air injection over medium or none air injection.
Clocking Effects of Inlet Non-Uniformities in a Fully Cooled High-Pressure Vane: A Conjugate Heat Transfer Analysis
Authors: Griffini Duccio , Insinna Massimiliano , Salvadori Simone , Martelli Francesco
Published: August 2015

A high-pressure vane equipped with a realistic film-cooling configuration has been studied. The vane is characterized by the presence of multiple rows of fan-shaped holes along pressure and suction side while the leading edge is protected by a showerhead system of cylindrical holes. Steady three-dimensional Reynolds-Averaged Navier-Stokes (RANS) simulations have been performed. A preliminary grid sensitivity analysis with uniform inlet flow has been used to quantify the effect of spatial discretization. Turbulence model has been assessed in comparison with available experimental data.

The effects of the relative alignment between combustion chamber and high-pressure vanes are then investigated considering realistic inflow conditions in terms of hot spot and swirl. The inlet profiles used are derived from the EU-funded project TATEF2. Two different clocking positions are considered: the first one where hot spot and swirl core are aligned with passage and the second one where they are aligned with the leading edge.

Comparisons between metal temperature distributions obtained from conjugate heat transfer simulations are performed evidencing the role of swirl in determining both the hot streak trajectory within the passage and the coolant redistribution. The leading edge aligned configuration is resulted to be the most problematic in terms of thermal load, leading to increased average and local vane temperature peaks on both suction side and pressure side with respect to the passage aligned case.

A strong sensitivity of both injected coolant mass flow and heat removed by heat sink effect has also been highlighted for the showerhead cooling system.
A New Test Facility to Investigate Film Cooling on a Non-Axisymmetric Contoured Turbine Endwall: Part II — Heat Transfer and Film Cooling Measurements
Authors: Kneer Johannes , Puetz Franz , Schulz Achmed , Bauer Hans-Jörg
Published: August 2015

The present work is part of a comprehensive heat transfer and film-cooling study on a locally cooled non-axisymmetric contoured turbine endwall. A new test rig consisting of a linear cascade of three prismatic vanes at unity scale and exchangeable endwall has been established. The rig is operated in an open-loop configuration at a reduced main gas temperature of 425 K, an exit Mach number of 0.5 and an exit Reynolds number of 1.6×106. Air is used both as main gas and coolant; a realistic density ratio is achieved by cooling the coolant below freezing. In Part I [1] of the study aerodynamic measurements are presented. This paper concentrates on film-cooling of the contoured endwall with special emphasis on data acquisition and reduction for the application of the superposition principle of film cooling. The first experimental results from thermographic measurements are discussed.
Scale-Adaptive and Large Eddy Simulations of a Turbulent Spray Flame in a Scaled Swirl-Stabilized Gas Turbine Combustor Using Strained Flamelets
Authors: Fossi Alain , deChamplain Alain , Paquet Bernard , Kalla Smail , Bergthorson Jeffrey M.
Published: August 2015

In this paper, the three-dimensional (3D) reacting turbulent two-phase flow field of a scaled swirl-stabilized gas turbine combustor is numerically investigated using the commercial CFD software ANSYS FLUENT™-v14. The first scope of this study aims to explicitly compare the predictive capabilities of two turbulence models namely Scale-Adaptive Simulation (SAS) and Large Eddy Simulation (LES) for a reasonable compromise between accuracy of results and global computational cost when applied to simulate swirl-stabilized spray combustion. The second scope of the study is to couple chemical reactions to the turbulent flow using a realistic chemistry model and also to model the local chemical non-equilibrium effects caused by turbulent strain. Standard Eulerian and Lagrangian formulations are used to describe both gaseous and liquid phases respectively. The fuel used is liquid jet-A1 which is injected in the form of a polydisperse spray and the droplet evaporation rate is calculated using the infinite conductivity model. One-component (n-decane) and two-component fuels (n-decane + toluene) are used as jet-A1 surrogates. The combustion model is based on the first and second moments of the mixture fraction, and a presumed-probability density function (PDF) is used to model turbulent-chemistry interactions. The instantaneous thermochemical state necessary for the chemistry tabulation is determined by using initially the partial equilibrium assumption (PEQ) and thereafter, the detailed non-equilibrium (NEQ) calculations through the laminar flamelet concept. The combustion chemistry of these surrogates is represented through a reduced chemical kinetic mechanism (CKM) comprising 1 045 reactions among 139 species, derived from the detailed jet-A1 surrogate model, JetSurf 2.0. Numerical results are compared with a set of published data for a steady spray flame. Firstly, it is observed that, by coupling the two turbulence models with a combustion model incorporating a representative chemistry to account for non-equilibrium effects with realistic fuel properties, the models predict reasonably well the main combustion trends, with a superior performance for LES in terms of trade-off between accuracy and computing time. Secondly, because of some assumptions with the combustion model, some discrepancies are found in the prediction of species slowly produced or consumed such as CO and H2. Finally, the study emphasizes the dominant advantage of an adequate resolution of the mixing characteristics especially with the more demanding simulation of a swirl-stabilized spray flame.
Numerical Investigations on the Aerodynamic Performance of Turbine Stage and Rotordynamic Characteristics of Stator Seal With Consideration of Supplementary Steam
Authors: Li Zhigang , Li Jun , Wang Shizhu , Ji Dawei , Xiao Gaohui , Zhai Xuefei
Published: August 2015

The supplementary steam structure is used in the high pressure cylinder to increase the power output of steam turbine through increase the mass flow rate. In this work, the supplementary steam structure installed between the fifth and sixth stage of the high pressure cylinder of steam turbine is taken as the research object. The flow field and aerodynamic performance of the fifth and sixth stage was numerically investigated at different supplement steam rates using the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and k–ε turbulent model solutions. The inlet/outlet boundary flow conditions of the stator labyrinth seal of the sixth stage was determined based on the steady computations at three different supplementary steam rates. The unsteady flow field and rotordynamic coefficients of the stator labyrinth seal were calculated using the multi-frequency elliptical whirling orbit model and dynamic grid technique based on the unsteady RANS solutions. The numerical results show that the supplementary steam jet impacts on the hub regions of the stator blade of the sixth stage and results in the vortex flow. This flow behavior leads to the non-uniform inlet aerodynamic parameters at the entrance of the stator blade of the sixth stage. The aerodynamic performance decreases with the increase of the supplementary steam rates. The supplementary steam jet changes the inlet preswirl and boundary flow condition of the stator labyrinth seal of the sixth stage. The fluid excitation rotordynamic coefficients of the stator labyrinth seal would change due to the variation of the boundary flow condition. The detailed flow pattern of the turbine stage and variation of the rotordynamic coefficients of the stator labyrinth seal at different supplementary steam rates were also illustrated and discussed.
Analytical and Numerical Investigations on the Aeroacoustical Oscillation of Flow Past the Cavity
Authors: Shao Weidong , Li Jun
Published: August 2015

Noise radiated by aeroacoustical oscillation of low Mach number flow past a two-dimensional cavity has been investigated analytically and numerically using electro-acoustical analogy and a hybrid scheme combining CFD with an implementation of the porous Ffowcs Williams-Hawkings equation. The noise generation mechanism is illustrated and the interaction between flow and cavity as well as key factors of resonant frequency is discussed. The 2D compressible unsteady Reynolds averaged Navier-Stokes equations (URANS) are solved to obtain near field acoustic source and unsteady characteristics of cavity flow. A buffer domain is exerted along all external boundaries to suppress boundary wave reflection. Computed tonal frequency and amplitude of pressure oscillations demonstrate good agreement with previous computational simulations and experiments. The influences of the length and shape of the neck and porous inserts on the noise radiated to the far field are also investigated. The 3D far field numerical results show that at a certain incoming flow velocity and shear layer thickness the frequency of the dominant oscillation increases with the length of the neck and the magnitude in the downstream far field is 8dB greater than that in the upstream far field. The increasing chamfer decreases the resonance frequency and changes the effective streamwise opening length resulting in significant differences in acoustic pressure fluctuation. The porous inserts on the floor of the cavity reduce the mass flow flux through the cavity neck and accordingly suppress the amplitude of dominant oscillation. The preliminary simulations reveal promising methods for sound radiation control.
Investigation of a Prefilming Airblast Atomizer With Respect to Surface Stripping
Authors: Volz Melanie , Konle Marco , Gebretsadik Mulubrhan , Habisreuther Peter , Zarzalis Nikolaos
Published: August 2015

One commonly used injection system in gas turbines is the prefilming airblast atomizer which creates a fuel film that should disintegrate at the end of the prefilmer. But under certain conditions droplets are separated from the film before reaching the end of the prefilmer. This phenomenon is called surface stripping. For the investigation of those conditions both an experimental and numerical setup are defined. The experiment measures the film thickness on the prefilmer with the help of the planar laser-induced fluorescence technique. For the numerical investigation the volume of fluid method together with a large eddy simulation of OpenFOAM® 2.1.1 is used. After the validation of the numerical model with the experimental data, the dependency of the mean film thickness from the relative velocity of air and water is investigated. It is shown that first the momentum flux ratio is not sufficient in describing the behavior of the film on the prefilmer and second a critical relative velocity has to be exceeded so that surface stripping can take place. Three flow regimes are observed by increasing the relative velocity: smooth film surface, wavy film surface and surface stripping. Due to the surface stripping the transferred fuel mass into the gas phase is increased rapidly.
Adiabatic Effectiveness and Flow Field Measurements in a Realistic Effusion Cooled Lean Burn Combustor
Authors: Andreini Antonio , Becchi Riccardo , Facchini Bruno , Mazzei Lorenzo , Picchi Alessio , Turrini Fabio
Published: August 2015

Over the last ten years there have been significant technological advances toward the reduction of NOx emissions from civil aircraft engines, strongly aimed at meeting stricter and stricter legislation requirements. Nowadays, the most prominent way to meet the target of reducing NOx emissions in modern combustors is represented by lean burn swirl stabilized technology. The high amount of air admitted through a lean-burn injection system is characterized by very complex flow structures such as recirculations, vortex breakdown and precessing vortex core, that may deeply interact in the near wall region of the combustor liner. This interaction makes challenging the estimation of film cooling distribution, commonly generated by slot and effusion systems.

The main purpose of the present work is the characterization of the flow field and the adiabatic effectiveness due to the interaction of swirling flow, generated by real geometry injectors, and a liner cooling scheme made up of a slot injection and an effusion array. The experimental apparatus has been developed within EU project LEMCOTEC and consists of a non-reactive three sectors planar rig; the test model is characterized by a complete cooling system and three swirlers, replicating the geometry of a GE Avio PERM (Partially Evaporated and Rapid Mixing) injector technology.

Flow field measurements have been performed by means of a standard 2D PIV (Particle Image Velocimetry) technique, while adiabatic effectiveness maps have been obtained using PSP (Pressure Sensitive Paint) technique. PIV results show the effect of coolant injection in the corner vortex region, while the PSP measurements highlight the impact of swirled flow on the liner film protection separating the contribution of slot and effusion flows. Furthermore an additional analysis, exploiting experimental results in terms of heat transfer coefficient, has been performed to estimate the net heat flux reduction (NHFR) on the cooled test plate.
A Comparison of Modelling Techniques for Polydispersed Droplet Spectra in Steam Turbines
Authors: Hughes Fiona R. , Starzmann Jörg , White Alexander J. , Young John B.
Published: August 2015

Within steam turbine flows, condensation phenomena give rise to complex droplet spectra that can span more than two orders of magnitude in size. To predict the behaviour of the two-phase flow and the resulting losses, the interactions between the vapour phase and droplets of all sizes must be accurately calculated. The estimation of thermodynamic losses and droplet deposition rates, in particular, depend on the size range and shape of the droplet spectrum. These calculations become computationally burdensome when a large number of droplet groups are present, and it is therefore advantageous to capture the complete droplet spectrum in a compressed form. This paper compares several methods for reducing the complexity of the droplet spectrum: a single representative droplet size (equivalent monodispersion), the moment method (including various growth rate approximations), the quadrature method of moments, and spectrum pruning. In spectrum pruning, droplet groups are individually nucleated, but their number is subsequently reduced by combining groups together in a manner that preserves droplet number, wetness fraction, and the shape of the initial spectrum. The various techniques are compared within a Lagrangian framework by tracking the two-phase behaviour along predefined pressure-time trajectories. Primary and secondary nucleation, droplet evaporation, and a representative turbomachinery case are modelled. The calculations are compared in terms of speed, accuracy, and robustness. It is shown that both the moment methods and spectrum pruning provide an appreciable improvement in accuracy over the use of an ‘equivalent’ monodispersion without compromising calculation speed. Although all the examined methods are adequate for primary nucleation and droplet growth calculations, spectrum pruning and the quadrature method of moments are most accurate over the range of conditions considered.
The Effect of Fuel Composition on Combustion Instability Mode Occurrence in a Model Gas Turbine Combustor
Authors: Yoon Jisu , Joo Seongpil , Lee Min Chul , Kim Jeongjin , Oh Jaeyo , Yoon Youngbin
Published: August 2015

Recently, energy resource depletion and unstable energy prices have become global issues. Worldwide pressure to secure and make more gas and oil available to support global power needs has increased. To meet these needs, alternative fuels composed of various types of fuels have received attention, including biomass, dimethyl ether (DME), and low rank coal. For this reason, the fuel flexibility of the combustion system becomes more important. In this study, H2 and CH4 were selected as the main fuel composition variables and the OH-chemiluminescence measurement technique was also applied. This experimental study was conducted under equivalence ratio and fuel composition variations with a model gas turbine combustor to examine the relation between combustion instability and fuel composition. The combustion instability peak occurs in the H2/CH4 50:50 composed fuel and the combustion instability frequency shifted to higher harmonic of longitudinal mode based on the H2 concentration of the fuel. Based on instability mode and flame length calculation, the effect of the convection time during the instability frequency increasing phenomenon was found in a partially premixed gas turbine combustor. The time-lag analysis showed that the short convection time in a high H2 concentration fuel affects the feedback loop period reduction and, in these conditions, high harmonics of longitudinal mode instability occurs.

This fundamental study on combustion instability frequency shifting characteristics was conducted for H2/CH4 composed fuel and the results contribute key information for the conceptual design of a fuel flexible gas turbine and its optimum operation conditions.
Coupled Aero-Thermal Modeling of a Rotating Cavity With Radial Inflow
Authors: Sun Zixiang , Amirante Dario , Chew John W. , Hills Nicholas J.
Published: August 2015

Flow and heat transfer in an aero-engine compressor disc cavity with radial inflow has been studied using computational fluid dynamics (CFD), large eddy simulation (LES) and coupled fluid/solid modelling. Standalone CFD investigations were conducted using a set of popular turbulence models along with 0.2° axisymmetric and a 22.5° discrete sector CFD models. The overall agreement between the CFD predictions is good, and solutions are comparable to an established integral method solution in the major part of the cavity. The LES simulation demonstrates that flow unsteadiness in the cavity due to the unstable thermal stratification is largely suppressed by the radial inflow. Steady flow CFD modelling using the axisymmetric sector model and the Spalart-Allmaras turbulence model was coupled with a finite element (FE) thermal model of the rotating cavity. Good agreement was obtained between the coupled solution and rig test data in terms of metal temperature. Analysis confirms that use of a small radial bleed flow in compressor cavities is effective in reducing thermal response times for the compressor discs and that this could be applied in management of compressor blade clearance.
Assessment of Unsteady Pressure Measurement Uncertainty: Part 2 — Virtual Three Hole Probe
Authors: Dell’Era Giulia , Mersinligil Mehmet , Brouckaert Jean-François
Published: August 2015

With the advancements in miniaturization and temperature capabilities of piezo-resistive pressure sensors, pneumatic probes — which are the long established standard for flow-path pressure measurements in gas turbine environments — are being replaced with unsteady pressure probes. On the other hand, any measured quantity is by definition inherently different from the ‘true’ value, requiring the estimation of the associated errors for determining the validity of the results and establishing respective confidence intervals. In the context of pressure measurements, the calibration uncertainty values, which differ from measurement uncertainties, are typically provided. Even then, the lack of a standard methodology is evident as uncertainties are often reported without appropriate confidence intervals. Moreover, no time-resolved measurement uncertainty analysis has come to the attention of the authors.

The objective of this paper is to present a standard method for the estimation of the uncertainties related to measurements performed using single sensor unsteady pressure probes, with the help of measurements obtained in a one and a half stage low pressure high speed axial compressor test rig as an example. The methodology presented is also valid for similar applications involving the use of steady or unsteady sensors and instruments.

The static calibration uncertainty, steady measurement uncertainties and unsteady measurement uncertainties based on phase-locked and ensemble averages are presented by the authors in [1]. Depending on the number of points used for the averaging, different values for uncertainty have been observed, underlining the importance of having greater number of samples. For unsteady flows, higher uncertainties have been observed at regions of higher unsteadiness such as tip leakage vortices, hub corner vortices and blade wakes.

Unfortunately, the state of the art in single-sensor miniature unsteady pressure probes is comparable to multi-hole pneumatic probes in size, preventing the use of multi-hole unsteady probes in turbomachinery environments. However, the angular calibration properties of a single sensor probe obtained via an aerodynamic calibration may further be exploited as if a three-hole directional probe is employed, yielding corrected total pressure, unsteady yaw angle, static pressure and Mach number distributions based on the phase-locked averages with the expense of losing the time-correlation between the virtual ports. The aerodynamic calibration and derivation process are presented together with the assessment of the uncertainties associated to these derived quantities in this contribution. In the virtual three-hole mode, similar to that of a single-sensor probe, higher uncertainty values are observed at regions of higher unsteadiness.
Steady and Unsteady CFD Calculation of the Laminar-to-Turbulent Transition in a Turning Mid Turbine Frame With Embedded Design
Authors: Bader Pascal , Sanz Wolfgang
Published: August 2015

In order to meet the weight requirements of future jet engines S-shaped intermediate turbine ducts can be supplied with turning load carrying struts in order to save the first vane row of the subsequent low pressure rotor.

In such a duct large flow structures emanating from the outlet of the transonic high pressure stage are transported towards the low pressure rotor and are superimposed by secondary effects generated by the turning struts within the duct. To reduce the fluctuations behind the S-shaped duct and to homogenize the flow, the duct can be equipped with additional splitters. Such an embedded design has the advantage of a more homogenized flow entering the low pressure rotor, thus improving efficiency.

It is crucial for the overall efficiency to optimize the design of such an intermediate turbine duct. To understand all flow effects it is helpful to perform CFD calculations which do not neglect laminar-to-turbulent transition. Therefore this paper presents steady and unsteady CFD results of an S-shaped turbine duct with splitters considering boundary layer transition using Menter’s γ-ReΘ model. The differences between steady and unsteady simulation and the influence of transition are discussed.
CFD Modeling of Low Pressure Steam Turbine Radial Diffuser Flow by Using a Novel Multiple Mixing Plane Based Coupling: Simulation and Validation
Authors: Stein Peter , Pfoster Christoph , Sell Michael , Galpin Paul , Hansen Thorsten
Published: August 2015

The diffuser and exhaust of low pressure steam turbines shows significant impact on the overall turbine performance. The amount of recovered enthalpy leads to a considerable increase of the turbine power output, and therefore a continuous focus of turbine manufacturers is put on this component. On the one hand, the abilities to aerodynamically design such components is improved, but on the other hand a huge effort is required to properly predict the resulting performance and to enable an accurate modeling of the overall steam turbine and therewith plant heat rate. A wide range of approaches is used to compute the diffuser and exhaust flow, with a wide range of quality. Today it is well known and understood, that there is a strong interaction of rear stage and diffuser flow, and the accuracy of the overall diffuser performance prediction strongly depends on a proper coupling of both domains. The most accurate, but also most expensive method is currently seen in a full annulus and transient coupling. However, for a standard industrial application of diffuser design in a standard development schedule, such a coupling is not feasible and more simplified methods have to be developed.

The paper below presents a CFD modeling of low pressure steam turbine diffusers and exhausts based on a direct coupling of the rear stage and diffuser using a novel multiple mixing plane. It is shown that the approach enables a fast diffuser design process and is still able to accurately predict the flow field and hence the exhaust performance. The method is validated against several turbine designs measured in a scaled low pressure turbine model test rig using steam. The results show a very good agreement of the presented CFD modeling against the measurements.
Design of a Single Stage Turbine for the Quantification of Aerodynamic Damping
Authors: Meinzer Christopher E. , Bittner Simon L. , Schmitt Stefan , Kielb Robert E. , Seume Joerg R.
Published: August 2015

For an experimental study of aerodynamic damping in an axial low pressure turbine, a single stage subsonic turbine blisk is designed and aerodynamically and aeromechanically assessed. The design goals are a low aerodynamic damping, to allow a long ring down of blade vibration, and aeromechanical stable operating points.

With respect to these requirements, the aeromechanical analysis is executed using a time-linearized RANS method. The results of the final design are compared with another independent implementation of this method. Further, a preliminary flutter design tool is used to predict flutter stability and to cover the full range of current design tools. The rotor blading is manufactured as a blade integrated disk to eliminate friction damping in the planned experiment on the quantification of aerodynamic damping. To complement the study and to discuss the influence of damping, an experimental modal analysis of the manufactured blisk is completed to identify the frequency response and the damping.
Development of a Jet-Stabilized Low-Emission Combustor for Liquid Fuels
Authors: Zizin Anton , Lammel Oliver , Severin Michael , Ax Holger , Aigner Manfred
Published: August 2015

In this work the ongoing development of a jet-stabilized FLOX®(Flameless Oxidation)-type low-emission combustor for liquid fuels is described. The desired application of this concept is a micro gas turbine range extender for next generation car concepts. Diesel DIN EN 590 was used to operate the combustor, which is very similar to other fuels like bio-diesel, light heating oil and kerosene and therefore provides a link to other gas turbine applications in power generation. The investigation of flame stabilization of jet flames as well as fuel atomization, spray dispersion and evaporation is essential for the design of an effective and reliable combustor for liquid fuels. An axisymmetric single-nozzle combustion chamber was chosen for the initial setup. A variety of burner configurations was tested in order to investigate the influence of different design parameters on the flame shape, the flame stability and emissions. Two pressure atomizers and one air-blast atomizer were combined with two types of air nozzles and two different burner front plates (axisymmetric and off-centered jet nozzle). Finally, a twelve nozzle FLOX® combustor with pre-evaporator was designed and characterized. The combustor was operated at atmospheric pressure with preheated air (300° C) and in a range of equivalence ratios φ between 0.5 and 0.95 (λ = 1.05–2). The maximum thermal power was 40 kW. For each combustor configuration and operating condition the flame shape was imaged by OH*-chemiluminescence, together with an analysis of the exhaust gas emissions. Laser sheet imaging was used to identify the spray geometry for all axisymmetric combustors. Wall temperatures were measured for two configurations using temperature sensitive paints, which will be utilized in future CFD modeling. The results show a dependence of NOx emissions on the flame’s lift-off height, which in turn is defined by the spray properties and evaporation conditions. The tendency to soot formation was strongly dependent on the correlation of the recirculation zone to the spray cone geometry. In particular, strong soot formation was observed when unevaporated droplets entered the recirculation zone.
Thermo-Mechanical Rotor Analysis Tuned by Engine Operational Data
Authors: Bruzzone Silvia , Mantero Marco , Patrone Stefano , Santolini Benedetto M. , Silingardi Andrea , Traversone Laura
Published: August 2015

Gas turbine engines must withstand severe thermo-mechanical conditions during present-day load operation, characterized by cyclic transients and long dwell times. Indeed engine components are subject to thermal transient conditions, thermo-mechanical strain and stress fields; those are not easily measurable during operation, making calculations hardly confirmable. All these operational factors can lead a turbine component life reduction, finally increasing lifetime costs.

The developed approach has been based on several calculations, such as thermal and FEM stress evaluation on the rotor components, tuned or validated by different field measurements carried out by thermocouples in the rotor core and the pre-tightening load variation of tie-rod. Transient disks and tie-rod temperatures (calculated by an in-house Secondary Air System code) have been tuned on experimental data. Thus, for rotor thermo-mechanical analysis more reliable boundary conditions have been provided. Rotor FEM analysis has been finally checked comparing the variation of the tie-bolt tension (calculated by FEM analysis) with the experimental behaviour observed during different operating conditions.
Numerical Investigation of the Influence of Flow Parameters Nonuniformity at the Diffuser Inlet on Characteristics of the GTE Annular Combustion Chamber
Authors: Matveev Sergey S. , Zubrilin Ivan A. , Orlov Mikhail Yu. , Matveev Sergey G.
Published: August 2015

Parameters at a combustion chamber’s inlet significantly vary in an aircraft engine’s transient states of operation. At the same time, there is a significant spatial heterogeneity of flow parameters at a diffuser inlet of a combustion chamber, which is defined by nature of flow in a compressor and an individual for each mode of operation of a specific gas generator. In this paper presented a study of an influence of radial and circumferential nonuniformities of flow parameters on characteristics of a combustion chamber. Multi spray for annular combustion chamber with two rows of burner is considered. Z-shaped sector, which contains two nozzles of outer and two nozzles of inner row, was selected as the calculated domain. Calculations were carried out in ANSYS Fluent 14.5 software package with an implementation of cluster analysis. Nonuniformity at a diffuser inlet was set as fifth degree polynomial, which was derived from a numerical simulation of a compressor. As a result it was established, that radial nonuniformity of flow parameters at an inlet of a combustion chamber influences on characteristics of a combustion chamber. A stretched shape of velocity profile contributes to higher air flow dynamic pressure on dome than using uniform profile air velocity. At that, local equivalents ratio excess are changing, and consequently, sizes and location NOx production zones are changing as well. The residual rotation of flow from the compressor leads to a lesser effect on total pressure drop and air distribution in flame tube. The obtained results showed that, during a design of a combustion chamber, it is necessary to take into account nonuniformity of parameters’ distribution at its inlet.