bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combustion and Oxidation Kinetics of Alternative Gas Turbines Fuels
Authors: Glaude Pierre-Alexandre , Sirjean Baptiste , Fournet René , Bounaceur Roda , Vierling Matthieu , Montagne Pierre , Molière Michel 
Published: September 2014

Heavy duty gas turbines are very flexible combustion tools that accommodate a wide variety of gaseous and liquid fuels ranging from natural gas to heavy oils, including syngas, LPG, petrochemical streams (propene, butane…), hydrogen-rich refinery by-products; naphtha; ethanol, biodiesel, aromatic gasoline and gasoil, etc. The contemporaneous quest for an increasing panel of primary energies leads manufacturers and operators to explore an ever larger segment of unconventional power generation fuels. In this moving context, there is a need to fully characterize the combustion features of these novel fuels in the specific pressure, temperature and equivalence ratio conditions of gas turbine combustors using e.g. methane as reference molecule and to cover the safety aspects of their utilization.
A numerical investigation of the combustion of a representative cluster of alternative fuels has been performed in the gas phase, namely two natural gas fuels of different compositions, including some ethane, a process gas with a high content of butene, oxygenated compounds including methanol, ethanol, and DME (dimethyl ether). Sub-mechanisms have specifically been developed to include the reactions of C4 species. Major combustion parameters, such as auto-ignition temperature (AIT), ignition delay times (AID), laminar burning velocities of premixed flames, adiabatic flame temperatures, and CO and NOx emissions have then been investigated. Finally, the data have been compared with those calculated for methane flames.
These simulations show that the behaviors of alternative fuels markedly differ from that of conventional ones. Especially, DME and the process gases appear to be highly reactive with significant impacts on the auto-ignition temperature and flame speed data, which justifies burner design studies within premixed combustion schemes and proper safety considerations. The behaviors of alcohols (especially methanol) display some commonalities with those of conventional fuels. In contrast, DME and process gas fuels develop substantially different flame temperature and NOx generation rates than methane. Resorting to lean premix conditions is likely to achieve lower NOx emission performances. This review of gas turbine fuels shows for instance that the use of methanol as a gas turbine fuel is possible with very limited combustor modifications.
Performance Investigation Into Supersonic Diffuser for a High Pressure Centrifugal Compressor
Authors: Sugimoto Takao , Kawanishi Tsukinami , Kumamaru Hiroshige , Tohbe Yasumasa 
Published: September 2014

In high pressure centrifugal compressors, the overall stage performance is greatly influenced by its diffuser performance. Extremely complicated non-uniform and unsteady flow exists in the region between the impeller exit and the diffuser inlet. Furthermore, in the case of supersonic diffuser, shock waves can be observed near the diffuser inlet. These can cause aerodynamic losses. Therefore, it is essential to recognize such complicated flow to realize an appropriate diffuser design.
An investigation into the performance of supersonic diffuser was carried out using a high pressure compressor test rig for a small industrial gas turbine with a high back swept impeller and a quasi pipe-shaped channel diffuser.
In addition, 3D quasi-unsteady flow analyses of the entire compressor by a RANS code with Non Linear Harmonic method at several operating conditions between surge and choke were conducted to investigate the details of unsteady flow between the impeller exit and the diffuser exit.
The results of the performance test and that of the 3D unsteady flow analyses have shown good agreement in the pressure rise and the isentropic efficiency at several operating conditions. These support high accuracy of the flow analyses and the performance measurements.
Secondary Flows, Endwall Effects and Stall Detection in Axial Compressor Design
Authors: Banjac Milan , Petrovic Milan V. , Wiedermann Alexander 
Published: September 2014

This paper describes a methodology and a fully tested and calibrated mathematical model for the treatment of endwall effects in axial compressor aerodynamic calculations. Additional losses and deviations caused by the clearance and secondary flows are analyzed. These effects are coupled with endwall boundary layer losses and blockage development. Stall/surge detection is included and mutual interaction of different loss mechanisms is considered.
Individual mathematical correlations for different effects have been created or adopted from earlier papers with the aim of forming one integral model that is completely described in this paper. Separate mathematical correlations and calibration measures are discussed in detail in the first part of the paper.
The developed overall model is suitable for application in two-dimensional or mean-line compressor flow calculations. During the development, it was tested, calibrated and validated using throughflow calculations comparing numerical results with experimental data for a large number of test cases. These test cases include compressors with very different configurations and operating ranges. The data on the compressors were taken from the open literature or obtained from industrial partners.
Corrosion and Erosion Behavior in Supercritical CO2 Power Cycles
Authors: Fleming Darryn , Kruizenga Alan , Pasch James , Conboy Tom , Carlson Matt 
Published: September 2014

Supercritical Carbon Dioxide (S-CO2) is emerging as a potential working fluid in power-production Brayton cycles. As a result, concerns have been raised regarding fluid purity within the power cycle loops. Additionally, investigations into the longevity of the S-CO2 power cycle materials are being conducted to quantify the advantages of using S-CO2 versus other fluids, since S-CO2 promises substantially higher efficiencies. One potential issue with S-CO2 systems is intergranular corrosion [1]. At this time, Sandia National Laboratories (SNL) is establishing a materials baseline through the analysis of 1) “as received” stainless steel piping, and 2) piping exposed to S-CO2 under typical operating conditions with SNL’s Brayton systems. Results from ongoing investigations are presented.
A second issue that SNL has discovered involves substantial erosion in the turbine blade and inlet nozzle. It is believed that this is caused by small particulates that originate from different materials around the loop that are entrained by the S-CO2 to the nozzle, where they impact the inlet nozzle vanes, causing erosion. We believe that, in some way, this is linked to the purity of the S-CO2, the corrosion contaminants, and the metal particulates that are present in the loop and its components.
Performance Improvement of Multistage Centrifugal Compressor With Low Flow-Rate Stages Based on Factory Acceptance Test Data
Authors: Tamaki Hideaki , Kawakubo Tomoki , Unno Masaru , Abe Shinji , Majima Kanji 
Published: September 2014

This study reports on the process of performance improvement in a six-stage compressor which encountered rotor vibration near its design flow rate during a factory acceptance test. This multistage compressor comprised three blocks, each of which also included a two-stage compressor. Flow instability in the 2nd or 3rd block, i.e. any of the 3rd to 6th stages, was suspected as the cause of the rotor vibration. This paper shows the process used to determine a modification plan to enhance the stable operating range; based on data obtained by a factory acceptance test.
The performance of each block was measured in that test, but not that of each stage. Improving the compressor performance therefore requires a new database, which represents the stage characteristics as operated during the factory acceptance test. A new database was thus constructed using a 1-D performance prediction method, the loss models of which were tuned to reproduce each block performance obtained by the factory acceptance test. Subsequently, stage-stacking calculations were conducted based on this database and modification plans devised, while single-stage tests for the 3rd and 6th stages were also conducted in a test stand to make a final decision on modification. This paper reports on both these results and data-reduction procedures.
Scaling Methods for Matching Tasks in Turbocharged Engines
Authors: Njoya Thibaut , Nakhjiri Mehdi , Pelz Peter F. , Frase Robert 
Published: September 2014

Specific turbocharger parameters are necessary to develop and match model based control strategies in the air path of a turbocharged engine. These parameters describe the turbocharger performance and are obtained from measurements on manufacturers’ standard test benches under steady state conditions and without taking into account the heat transfer between the components of the turbocharger or between the turbocharger and the surroundings. The latter falsifies the measured turbocharger efficiency which can be referred as “apparent efficiency”. The efficiency is a key parameter of the model based controls. Thus, the apparent efficiency increases the uncertainties (mismatching) and slows down the matching process considerably.
Due to the mismatching, manufacturers’ parameters themselves need to be calibrated. The calibration occurs on the basis of on-board measurements and offline analyses. However, this calibration procedure is not axiomatic and the results remain typical for a certain turbocharger and engine combination. Hence, it is usually not possible to apply the results when the same turbocharger should be matched with another engine.
A physically based scaling method has already been introduced in previous publications in order to obtain the “real” from the “apparent” efficiency, [1]. This work aims to show on the basis of a concrete example how the implementation of this method counteracts the mismatching without any further measurements. As a result, the matching process can be accelerated and enhanced. The reusability of the results leads to faster processes and lower costs.
Two-Phase Flow Modeling and Measurements in Low-Pressure Turbines: Part 1 — Numerical Validation of Wet Steam Models and Turbine Modeling
Authors: Grübel M. , Starzmann J. , Schatz M. , Eberle T. , Vogt D. M. , Sieverding F. 
Published: September 2014

In this publication an overview of the current state of wetness modeling at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) is given. For the modeling an Euler-Euler method implemented in the commercial flow solver ANSYS CFX is used. This method is able to take into account the non-equilibrium state of the steam and models the interactions between the gaseous and liquid phases.
This paper is the first part of a two-part publication and deals with the numerical validation of wet steam models by means of condensing nozzle and cascade flows. A number of issues with regard to the quality of the CFD code and the applied condensation models are addressed comparing the results to measurements. It can be concluded, that a calibration of the models is necessary to achieve a satisfying agreement with the experimental results.
Moreover, the modeling of the low pressure model steam turbine operated at the ITSM is described focusing on the asymmetric flow field in the last stage caused by the axial-radial diffuser. Different simplified axisymmetric diffuser models are investigated in steady state simulations and the results and the arising issues for part-load, design-load and over-load conditions are discussed. Thereafter, a comparison between the equilibrium and non-equilibrium steam modeling approaches is performed and the advantage of the non-equilibrium model is highlighted.
The second part of the publication focuses on experimental investigations and compares the numerical results to wetness measurement data, see Schatz et al. [1]. For this purpose, also different load conditions are considered.
Analysis of the Heat Transfer Driving Parameters in Tight Rotor Blade Tip Clearances
Authors: Lavagnoli S. , De Maesschalck C. , Paniagua G. 
Published: September 2014

Turbine rotor tips and casings are vulnerable to mechanical failures due to the extreme thermal loads they undergo during engine operation. In addition to the heat flux variations during the transient phase, high-frequency unsteadiness occurs at every rotor passage, with amplitude dependent on the tip gap. The development of appropriate predictive tools and cooling schemes requires the precise understanding of the heat transfer mechanisms. The present paper analyzes the nature of the overtip flow in transonic turbine rotors running at tight clearances, and explores a methodology to determine the relevant flow parameters that model the heat transfer.
Steady-state three-dimensional Reynolds-Averaged Navier-Stokes calculations were performed to simulate engine-like conditions considering two rotor tip gaps, 0.1% and 1% of the blade span. At tight tip clearance, the adiabatic wall temperature is not anymore independent of the solid thermal boundary conditions. The adiabatic wall temperature predicted with the linear Newton’s cooling law was observed to rise to non-physical levels in certain regions within the rotor tip gap, resulting in unreliable convective heat transfer coefficients. This paper investigates different approaches to estimate the relevant flow parameters that drive the heat transfer. The present study allows experimentalists to retrieve information on the gap flow temperature and convective heat transfer coefficient based on the use of wall heat flux measurements. Such approach is required to improve the accuracy in the evaluation of the heat transfer data while enhancing the understanding of tight-clearance overtip flows.
Numerical Investigation of Film Cooling Performance With Different Internal Flow Structures
Authors: Luo Jianxia , Liu Cunliang , Zhu Huiren 
Published: September 2014

Four coolant channel configurations, including supply plenum without crossflow, smooth channel with crossflow and ribbed channels with crossflow ( 135° and 45° angled ribs), are simulated to find out the effect of internal flow structures on the external film cooling performance. Reynolds Averaged Navier Stokes (RANS) simulations with realizable k-ε turbulence model and enhanced wall treatment are performed using a commercial code Fluent. Blowing ratios cover a range from 0.5 to 2.0. For the three cases with crossflow, a constant Reynolds number, ReDh, is fixed as 100000.
Particular attention has been paid to the flow structures and counter-rotating vortices. Helical motion of secondary flow is observed in the hole of the smooth case and the 45° ribs case, inducing strong velocity separation in the cooling hole and blocks at the entrance and exit. In the two cases, the cooling-air jet divides into two parts after being blown out of the hole and a pair of skewed vortices appears downstream. In the 135° ribs case, the vortex in the upper half region of the secondary flow channel rotates in the same direction with the hole inclination direction, the straight stream lines are generated and therefore lower loss and higher discharge coefficient. Experimental data of the smooth case and the 135° ribs case show the good agreement with the numerical results.
Simulation of Combustor/NGV Interaction Using Coupled RANS Solvers: Validation and Application to a Realistic Test Case
Authors: Insinna Massimiliano , Salvadori Simone , Martelli Francesco 
Published: September 2014

Numerical techniques are commonly used during both design and analysis processes, mainly considering single components. Technological progress asks for advanced approaches that include real-machine conditions and analyze components interaction, especially considering the combustor/turbine coupling. Modern combustors operate with strong swirl motions in order to obtain an adequate flame stabilization, generating a very complex flow field characterized by high turbulence level. These aspects affect performance of downstream components which are subjected to very aggressive inlet flow conditions: non-uniform total temperature, non-uniform total pressure, swirl and high turbulence intensity. For these reasons coupled analysis of combustor and turbine is necessary to accurately predict aero-thermal aspects that influence performance and reliability of these two components.
From a numerical point of view the simulation of a single domain characterized by a reactive flow with very different Mach number regimes (from low-Mach flow in combustion chamber to transonic flow in turbine) is problematic due to the different numerical requirements needed, especially concerning stability and accuracy. These problems could be overcome using coupled methods to simultaneously simulate combustor and turbine in separated domains which are managed by different solvers that communicate with each other.
A coupling method for the study of combustor/turbine interaction using the RANS methodology is proposed. In the first part of the paper the method is described and validated. The second part is dedicated to the application of the proposed coupling methodology to a realistic test case consisting of a model annular combustor and the Nozzle Guide Vane (NGV) of the MT1 high-pressure turbine stage. A commercial solver and an in-house code are respectively used for the simulation of combustor and NGV.
Results are presented and analyzed highlighting the importance of such type of simulations in understanding aero-thermal phenomena that characterize combustor/vane interaction.
Modelling Thermal Ageing Embrittlement in Turbine Rotors Using Neural Networks
Authors: Nappini Duccio , Zonfrillo Giovanni 
Published: September 2014

An artificial neural network-based algorithm, which adequately captures the complexity of the temper embrittlement phenomenon in NiCrMoV steels has been developed in order to predict the FATT50% value of material as a function of the chemical composition and serviced time. The model, validated using published data, relies for its training on a very large experimental data set of serviced rotors, aged up to 88,000 hours, and it captures the interactions between input parameters using complex non-linear functions.
The results agree with considerations reported in literature and provide analytical relations between evolution of the FATT50% value at various ageing time for a specific alloy compositions, as well as the influence of the main elements in the alloy composition.
Crack Growth Under Cyclic Loading and Plasticity Conditions
Authors: Szwedowicz Jaroslaw , Bednarz Piotr , Meilgen Christoph , Samuelson Jeff 
Published: September 2014

The increasing use of renewable energy sources to produce electricity requires additional operational flexibility from fossil-fuel gas and steam turbines. To compensate for renewable energy fluctuations in the electrical grid, a gas turbine (GT) engine needs to be more flexible, operating in peaking and partial loading modes as well as the base-load operation mode. Understanding how these different modes affect the lifetime of turbine components is critical to ensuring favourable RAM (Reliability, Availability, and Maintainability).
Component lifetimes in peaking modes are limited by the number of thermo-mechanical cycles that a component can experience before crack initiation. The useful lifetime of some components can be increased by basing the predicted lifetime on the number of cycles for crack initiation plus the number of cycles for the crack to reach its maximum allowable length based on the fracture toughness K1C criterion for linear elastic fracture mechanics (LEFM). This is usually accomplished by using the Paris law to predict the rate of crack growth. Once cracks are formed, further propagation depends on the states of stress and strain near the cracks. These factors, which drive crack growth, can be quantified by the energy release rate. The Paris law predicts crack growth as a function of the energy release rate under linear elastic conditions, commonly for load controlled tests with load ration R>0. However, large thermal and mechanical loading can result in plastic deformation under cyclic loading conditions.
Most GT components operate under strain controlled conditions generated by thermal loading. In this paper, a novel method is used to characterize crack growth under cyclic strain conditions in regions under plastic strain. The experimental data reveal that the rate of crack growth changes under plastic conditions in comparison with the linear elastic case. Especially compared to very high stress intensities ΔK of load controlled tests, here the allowable displacement limiting strain control matters. Applying experimental data from material tested under cyclic loading and elastic-plastic material response, component lifetime has been reliably predicted. Hereafter the developed method is referred to as elastic plastic fracture mechanics (EPFM) lifetime assessment. The EPFM approach more closely predicts the observed rate of crack growth than linear elastic fracture mechanics. LEFM over-predicts component lifetime for cracks growing in plastic regions under cyclic loading and could lead to catastrophic failure of a component. Therefore, the lifetime of a highly loaded component is more reliably assessed using the EPFM approach, as demonstrated for two alloys in this paper.
The Physics of H-Darrieus Turbine Starting Behaviour
Authors: Worasinchai Supakit , Ingram Grant L. , Dominy Robert G. 
Published: September 2014

This paper investigates Darrieus turbine starting behaviour and provides a resolution to the contradictory accounts of whether or not the Darrieus turbine can self-start. The paper builds on previous work proposing an analogy between the aerofoil in Darrieus motion and flapping-wing flow mechanisms. This analogy suggests that unsteadiness could be exploited to generate additional thrust and that this unsteady thrust generation is governed by rotor geometry.
To confirm the hypothesis, this investigation incorporated unsteady effects into a rotor analysis which resolved the differences between experiments and predictions made using a steady-state assumption.
The fundamental physics of starting were also studied and the rotor geometry parameters that govern the generation of unsteady thrust were explored: namely chord-to-diameter ratio and blade aspect ratio. Further simulation showed that the Darrieus rotor is prone to be locked in a deadband where the thrust is not continuous around a blade rotation. This discrete thrust is caused by the large variation of incidence angle during start-up making the Darrieus blade ineffective during part of the rotation.
The results also show that unsteady thrust can be promoted through an appropriate selection of blade aspect ratio and chord-to-diameter ratio and therefore it is possible to design rotors that have an ability to self-start. A new definition of self-starting is proposed based upon this improved understanding.