bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Influence of Diluent Gases on Combustion Properties of Natural Gas: A Combined Experimental and Modeling Study
Authors: Ermel Jörn , Richter Sandra , Kick Thomas , Braun-Unkhoff Marina , Naumann Clemens , Riedel Uwe 
Published: August 2015

Currently, new concepts for power generation are discussed, as a response to combat global warming due to CO2 emissions stemming from the combustion of fossil fuels. These concepts include new, low-carbon fuels as well as centralized and decentralized solutions. Thus, a more diverse range of fuel supplies will be used, with (biogenic) low-caloric gases such as syngas and coke oven gas (COG) among them. Typical for theses low-caloric gases is the amount of hydrogen, with a share of 50% and even higher. However, hydrogen mixtures have a higher reactivity than natural gas (NG) mixtures, burned mostly in today’s gas turbine combustors.
Therefore, in the present work, a combined experimental and modeling study of nitrogen-enriched hydrogen-air mixtures, some of them with a share of methane, to be representative for COG, will be discussed focusing on laminar flame speed data Su as one of the major combustion properties. Measurements were performed in a burner test rig at ambient pressure and at a preheat temperature T0 of 373 K. Flames were stabilized at fuel-air ratios between about φ = 0.5–2.1, depending on the specific fuel-air mixture.
This database was used for the validation of four chemical kinetic reaction models, including an in-house one, and by referring to hydrogen-enriched natural gas mixtures.
The measured laminar flame speed data of nitrogen-enriched methane-hydrogen-air mixtures are much smaller than the ones of nitrogen-enriched hydrogen-air mixtures. The grade of agreement between measured and predicted data depends on the type of flames and the type of reaction model as well as of the fuel-air ratio: good agreement was found in the fuel lean and slightly fuel rich regime; a large underprediction of the measured data exists at very fuel-rich ratios (φ > 1.4).
From the results of the present work, it is obvious that further investigations should focus on highly nitrogen-enriched methane-air mixtures, in particular for very high fuel-air ratio (φ > 1.4). This knowledge will contribute to a more efficient and a more reliable use of low-caloric gases for power generation.
An Experimental Study of the Aerodynamics and Performance of a Vertical Axis Wind Turbine in Confined and Non-Confined Environment
Authors: Dossena Vincenzo , Persico Giacomo , Paradiso Berardo , Battisti Lorenzo , Dell’Anna Sergio , Brighenti Alessandra , Benini Enrico 
Published: August 2015

This paper presents the results of a wide experimental study on an H-type Vertical Axis Wind Turbine (VAWT) carried out at Politecnico di Milano in the frame of the national founded project PRIN 2009. The experiments were carried out in the large-scale wind tunnel of the Politecnico di Milano, where real-scale wind turbines for micro generation can be tested in full similarity conditions. Integral torque and thrust measurements were performed, as well as detailed aerodynamic measurements to characterize the flow field generated by the turbine downstream of the rotor.
The machine was tested in both confined and non-confined environment, to highlight the effect of wind tunnel blockage on the aerodynamics and performance of the VAWT under investigation. The experimental results, compared with the blockage correlations presently available, suggest that specific correction models should be developed for VAWTs. The experimental thrust and power curves of the turbine, derived from integral measurements, exhibit the expected trends with a peak power coefficient of about 0.28 at tip-speed ratio λ = 2.5. Detailed flow measurements, performed in three conditions for λ equal to 1.5, 2.5 and 3.5, show the fully three-dimensional character of the wake, especially in the tip region where a non-symmetrical wake and tip vortex are found. The unsteady evolution of the velocity and turbulence fields further highlight the effect of aerodynamic loading on the wake unsteadiness, showing the time-dependent nature of the tip vortex and the onset of a non-symmetric dynamic stall for λ lower than 2.
Optimization of Compressor Variable Geometry Settings Using Multi-Fidelity Simulation
Authors: Reitenbach S. , Schnös M. , Becker R.-G. , Otten T. 
Published: August 2015

Variable geometry blade rows are a common instrument to avoid compressor instabilities which occur especially at low- and full-speed operation of gas turbines. The operating settings of variable stator vanes (VSVs) are typically obtained from expensive and time consuming performance rig tests and are not known during the early design phase of a gas turbine.
During preliminary design of the overall engine it is common practice to use default component characteristics based on considerable engineering experience. These can deviate substantially at off-design and often do not properly account for the impact of changes in component geometry. As a solution, multi-fidelity simulation often referred to as zooming or variable complexity analysis is applied. This proceeding facilitates a transfer of single component performance characteristics obtained in mid- or high-fidelity analysis to a full gas turbine system analysis based on lower resolution level.
The purpose of this study is to present a multidisciplinary numerical optimization methodology to define ideal blade row staggering of variable compressor stator vanes during the early preliminary design phase using multi-fidelity simulation. The objective of the resultant multi-dimensional constraint optimization is to find the best solution for the entire gas turbine system for a set of discrete operating points.
For the assessment a generic turbofan engine model is designed by taking into account top level engine requirements from an assumed airframe and flight mission scenario. Based on the performance calculation a full 3-D axial multistage high pressure compressor (HPC) is designed. The assumed design considerations are summarized and the modelling techniques are presented.
The optimization of VSV staggering mentioned above is carried out by re-staggering the variable geometry blade rows of the high-fidelity HPC and run a full 2-dimensional through-flow calculation. Results are then automatically transferred to the 0-dimensional engine model to calculate the engine overall performance. A Pareto optimized blade row staggering is found by taking into account the surge margin and the specific fuel consumption of the entire engine system as objective functions of the optimization process. Simultaneously several constraints such as DeHaller numbers and diffusion factors are considered. The optimization process chain and the tool coupling are summarized and described in detail. The resulting VSV staggering for a set of discrete operating points is shown.
Risk Assessment of Gas Turbines Rotors That Have Exceeded Their Design End of Life
Authors: Di Sisto Paolo , Benericetti Daniele 
Published: August 2015

The paper will describe the main outcomes of a risk assessment performed by General Electric O&G (GE O&G) in 2013 on a large number of gas turbine rotors that had exceeded their design end of life (EOL).
The assessment involves a large number of medium frames (e.g. MS3002J, MS5002C) plus small industrial gas turbines (e.g. MS1002, PGT10).
The design end of life is the lifespan inside which the risk of uncontained failure is expected to be improbable and this means the failure has a probability of occurrence of 0.12 total events or less during the life of five hundred gas turbines operating 8000 hours per year for 30 years [1].
GE gas turbine rotors are designed to operate with no need of inspection and maintenance till their design EOL (alias serviceable life).
The gas turbines end users may exceed EOL, provided the rotors have been subjected to a specific investigation that includes teardown and a full inspection.
The disregard of this recommendation may have catastrophic consequences on the gas turbines and on surrounding equipment and personnel.
Such recommendation was provided to customers the first time in 2005 through GETIL 1576 [2], the recommendation was renewed in 2013 with a new communication NIC 13.16 [3].
The risk assessment has essentially focused on rotating parts, because rotors (i.e. shaft, wheel, spacer) are the highest gas turbine energy components, that even if designed with high safety margins, they are not immune from time (e.g. creep) and/or cyclic dependent damage (e.g. fatigue).
The assessment has been carried out by following MIL-STD-882C [1] guidelines and in accordance to the principles defined by ISO 12100-2010 [4].
The failure risks have been estimated with the help of specific tools by using field data and life calculations performed with physics-based models.
The paper describes the methodology used to support the risk assessment and this means the “rotor life management methodology” that was developed by GE more than ten years ago, and was subsequently improved by including statistical assessments.
Combustor Heat Shield Impingement Cooling and its Effect on Liner Convective Heat Transfer for a Model Annular Combustor With Radial Swirlers
Authors: Gomez-Ramirez David , Dilip Deepu , Viswanath Ravi Bharath , Deshpande Samruddhi , Pandit Jaideep , Ekkad Srinath V. , Moon Hee-Koo , Kim Yong , Srinivasan Ram 
Published: August 2015

Increasing pressure to reduce pollutant emissions such as NOx and CO, while simultaneously increasing the efficiency of gas turbines, has led to the development of modern gas turbine combustors operating at lean equivalence ratios and high compression ratios. These modern combustors use a large portion of the compressor air in the combustion process and hence efficient use of cooling air is critical. Backside impingement cooling is one alternative for advanced cooling in gas turbine combustors. The dome of the combustor is a primary example where backside impingement cooling is extensively used. The dome directly interacts with the flame and hence represents a limiting factor for combustor durability. The present paper studies two aspects of dome cooling: the impingement heat transfer on the dome heat shield of an annular combustor and the effect of the outflow from the spent air on the liner heat transfer. A transient measurement technique using Thermochromic Liquid Crystals (TLCs) was used to characterize the convective heat transfer coefficient on the backside of an industrial heat shield design provided by Solar Turbines, Inc. for Reynolds numbers (with respect to the hole diameter) of ∼ 1500 and ∼ 2500. Reynolds-Averaged Navier Stokes (RANS) calculations using the k-ω SST turbulence model were found to be in good agreement with the experiment. A standard heat transfer correlation for impingement hole arrays overestimated the mean heat transfer coefficient compared to the experiment and computations, however this could be explained by low biases in the results.
Steady state IR measurements were performed to study the effects that the spent air from the heat shield impingement cooling had on the liner convective heat transfer. Measurements were taken for three Reynolds numbers (with respect to the hydraulic diameter of the combustor annulus) including 50000, 90000, and 130000. A downstream shift in the flow features was observed due to the secondary flow introduced by the outflow, as well as a significant increase in the convective heat transfer close to the dome wall.
Aerodynamic Redesign of a 5-Stage Axial Compressor by Re-Stagger and Bow
Authors: Ning Tao , Gu Chun-wei , Li Xiao-tang , Liu Tai-qiu , Xiao Yao-bing 
Published: August 2015

The paper is a preliminary methodology research of the aerodynamic redesign of a 5-stage axial compressor by re-stagger and bow with multistage CFD methods, with the purpose of developing the next upgrade version of this type of compressor. Prior to aerodynamic redesign, the validation study is carried out for overall performance, casing static pressure and spanwise total pressure profiles based on full-scale test data, proving that the multistage CFD applied is a relatively reliable tool for the analysis of the follow-up redesigning. Furthermore, at the near stall point, aerodynamic analysis demonstrates that significant separation exits in the last stator, which leads to the aerodynamic redesign focused on the last stator.
To explore the potential of aerodynamic improvement, it is focused on the aerodynamic redesign by re-stagger and bow. Multi-stage CFD methods are applied in the whole redesign process. Two steps of redesigning are applied for aerodynamic optimization. Upgrade 1 by re-stagger is used to adjust the operating points to more reasonable region, which contributes about 9 percent stall margin increase. Based on upgrade 1, an unconventional asymmetric bow configure is employed in upgrade 2 to reduce the high loss region dominated by mainstream. The redesigning exploitation by re-stagger and bow in this research produces a total 16% increase in stall margin.
Numerical Comparison of Rotordynamic Characteristics for a Fully-Partitioned Pocket Damper Seal and a Labyrinth Seal With High Positive and Negative Inlet Preswirl
Authors: Li Zhigang , Li Jun , Feng Zhenping 
Published: August 2015

Pocket damper seals are used as replacements for labyrinth seals in high-pressure centrifugal compressors at the balance piston location or center seal location to enhance rotordynamic stability. A concern exists that this enhanced stability will be lost at high positive inlet preswirl.
Numerical results of frequency-dependent rotordynamic force coefficients and leakage flow rates were presented and compared for a fully-partitioned pocket damper seal (FPDS) and a labyrinth seal at high positive and negative inlet preswirl, using a proposed transient CFD method based on the multi-frequency elliptical orbit whirling model. The negative preswirl indicates a fluid swirl in a direction opposite to rotor rotation at seal inlet. Both seals have identical diameter and sealing clearance. The full 3D concentric CFD model and mesh were built for the labyrinth seal and FPDS, respectively. The accuracy and availability of the present transient CFD numerical method were demonstrated with the experiment data of frequency-dependent rotordynamic coefficients of the labyrinth seal and FPDS at zero and high positive preswirl conditions. The numerical boundary conditions include two high positive preswirl, two high negative preswirl and a zero preswirl. Numerical results show that the effect of inlet preswirl on the direct force coefficients is weak, but the effect on the cross-coupling stiffness and effective damping is dramatic. Both two seals possess negative effective damping at lower excitation frequencies due to positive preswirl, and the crossover frequency of effective damping term increases with increasing positive preswirl. Negative preswirl produces negative cross-coupling stiffness and positive effective damping over the whole excitation frequency range. Increasing negative preswirl is a stabilizing factor for annular gas seals which results in a significant increase in the effective damping and a decrease in the crossover frequency. It is desirable to reduce the inlet preswirl to zero or even negative through applications of negative-swirl brakes and negative injection devices.
Heterogeneous Optimization Strategies for Carved and Squealer-Like Turbine Blade Tips
Authors: De Maesschalck C. , Lavagnoli S. , Paniagua G. , Verstraete T. , Olive R. , Picot P. 
Published: August 2015

Superior rotor tip geometries possess the potential to simultaneously mitigate aerodynamic losses and severe thermal loads onto the rotor overtip region. However, classical design strategies are usually constrained to a specific type of geometry, narrowing the spread of shape topologies considered during the design phase. The current paper presents two novel multi-objective optimization methodologies that enable the exploration of a broad range of distinct tip configurations for unshrouded rotor blades.
The first methodology is a shape optimization process that creates a fully carved blade tip shape defined through a Bezier surface controlled by 40 parameters. Combined with a differential evolution optimization strategy, this approach is applied to a rotor blade for two tip gap sizes: 0.85% (tight) and 1.38% (design) of the blade span. The second methodology is based on a topology optimization process that targets the creation of arbitrary tip shapes comprising one or multiple rims with a fixed height. The tip section of the blade has been divided into more than 200 separate zones, where each zone can be either part of an upstanding rim or part of the cavity floor. This methodology was tested with a level-set approach in combination with a differential evolution optimizer, and coupled to an optimization routine based on genetic algorithms.
The current study was carried out on a modern high-pressure turbine operating at engine-like Reynolds and high subsonic outlet Mach numbers. A fully hexahedral unstructured mesh was used to discretize the fluid domain. The aerothermal performance of each tip profile was evaluated accurately through RANS simulations adopting the SST turbulence model. Multi-objective optimizations were set for both design strategies that target higher aerodynamic rotor efficiencies and simultaneous minimization of the heat load.
This paper illustrates a wide variety of profiles obtained throughout the optimization and compares the performance of the different strategies. The research shows the potential of such novel methodologies to reach new unexplored types of blade tip designs with enhanced aerothermal performances.
Multi-Coordination of Actuators in Advanced Power Systems
Authors: Pezzini Paolo , Bryden Kenneth M. , Tucker David , Banta Larry 
Published: August 2015

Multi-coordination of actuators for a highly integrated, tightly coupled advanced power system was evaluated using the Hybrid Performance (Hyper) project facility at the U.S. Department of Energy’s National Energy Technology Laboratory (NETL). A two-by-two scenario in a fuel cell, turbine hybrid power system was utilized as a representative problem in terms of system component coupling during transients and setpoint changes. In this system, the gas turbine electric load is used to control the turbine speed, and the cold air bypass valve regulated fuel cell cathode mass flow.
Perturbations in the turbine speed caused by variations in the waste heat from the fuel cell affect the cathode airflow, and the cold-air bypass control action required for constant cathode airflow strongly affects the turbine speed. Previous implementation of two single-input, single-output (SISO) controllers failed to provide acceptable disturbance rejection and setpoint tracking under these highly coupled conditions. A multiple-input, multiple-output (MIMO) controller based on the classic internal model control (IMC) concept was implemented and experimentally tested for the first time using the Hyper project facility.
The state-space design of the MIMO configuration, the control law integration into the digital control platform, and the experimental comparison with the SISO case are presented.
The Effect of Aspect Ratio on Compressor Performance
Authors: To Ho-On , Miller Robert J. 
Published: August 2015

This paper considers the effect of aspect ratio on compressor performance. It is shown that the aspect ratio at which max efficiency occurs is relatively low, typically between 1 and 1.5. At these aspect ratios, decomposition of the flow field into freestream and endwall flows becomes difficult. In this paper, a unique approach is taken; McKenzie’s ‘linear repeating stage’ concept is used and a novel way of defining freestream flow is proposed. Through these simplifications and methods, physically accurate decomposition of the flow field for aspect ratios as low as ∼0.7 can be achieved.
This ability to accurately decompose the flow field leads to two key findings. Firstly, the commonly accepted relationship of endwall loss coefficient varying inversely with aspect ratio is inaccurate. Instead, a new term, which the authors refer to as ‘effective aspect ratio’, should replace aspect ratio. It is shown that not doing so can result in efficiency errors of ∼0.6% at low aspect ratios. Secondly, there exists a low aspect ratio limit below which the two endwall flows interact causing a large separation to occur along the span. From these findings, a low order model is developed to model the effect of varying aspect ratio on performance.
The last section of this paper uses this low order model as well as a simple analytical model to show that to a first order, the optimum aspect ratio is just a function of the loss generated by the endwalls at zero clearance and the rate of increase in profile loss due to blade thickness. This means that once the endwall configuration has been selected i.e. cantilever or shroud, the blade thickness sets the optimum aspect ratio.
Fuel Efficiency Optimization for a Divided Exhaust Period Regulated Two-Stage Downsized SI Engine
Authors: Hu Bo , Akehurst Sam , Brace Chris , Lu Pengfei , Copeland Colin D. , Turner J. W. G. 
Published: August 2015

In our previous paper, a new gas exchange concept termed Divided Exhaust Period Regulated 2-stage (DEP R2S) system has been proposed. In this system, two exhaust valves in each cylinder are separately functioned with one valve feeding the exhaust mass flow into the high pressure (HP) manifold whilst the other valve evacuating the remaining mass flow directly into the low pressure (LP) manifold. By adjusting the timing of the exhaust valves, the target boost can be controllable whilst improving the engine’s pumping work and scavenging is attainable which results in better fuel efficiency from the gas exchange perspective.
This paper will continue this study by adding an appropriate knock model to examine the benefits this concept could bring to the combustion phasing. The results at full load showed that under knock limited spark advance (KLSA) and fully optimized exhaust valve timing condition, the DEP R2S system benefited from lower pumping loss and better scavenging due to the reduced backpressure and improved pulsation interference despite suffering from reduced expansion ratio and expansion work. The combustion phasing was advanced across the engine speed which is mainly attributed to the reduced residual and the reduced requirement of gross IMEP. The net BSFC was observed to improve by up to 3% depending on the engine operating points. At part load, the DEP R2S system could be used as a mechanism to extend the ‘duration’ of the exhaust valve. This will reduce the recompression effect of the exhaust residuals during the beginning and the end of the exhaust stroke compared to the original R2S model with late exhaust valve opening and early exhaust valve opening. In addition, increased internal EGR due to the increased overlap between the LP and the intake valve is also beneficial for the improved PMEP as the throttle can be further opened to reduce the corresponding throttling loss. The average net BSFC improvement is expected to be approximately 6–7%.