bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of Premixed Gas Turbine Combustion System Fuel Flexibility With Increased Hydrogen Consumption in a Renewable Market Place
Authors: Bullard Timothy , Steinbrenner Alexander , Stuttaford Peter , Jansen Dennis , de Bruijne Theo
Published: August 2018

Gas turbine flexibility is key in markets with significant renewable energy resources. Operational load flexibility and fuel flexibility ensure the gas turbine remains competitive in supporting power generation in renewable markets. For applications where heat is required in support of a process industry the gas turbine offers an additional advantage. Alternate fuels such as hydrogen are generated as byproducts from chemical processing plants. Hydrogen also has the ability to be a ‘battery fuel’ as excess energy produced by wind and solar can be used to produce hydrogen through electrolysis. This work focuses on the retrofit and commercial introduction of significant quantities of hydrogen fuel into the gas supply of an existing commercial E-class gas turbine in Europe. The commercially operating plant provides combined heat (in the form of process steam) and power. The gas turbine operates with a lean premixed combustor without the need for diluent injection, and is able to operate flexibly with hydrogen mixed into the base natural gas fuel supply. The fuel mixing allows consumption of a chemical plant process gas resulting in positive economic and environmental benefit. This involves several considerations including combustor control/operation, safe flashback margin, emissions, stability and hardware durability. Enhancements to the control system through an automated combustor tuning package which is able to compensate real time for fluctuations in fuel gas constituents was implemented. Significant testing of the fuel flexible concept in a full scale high pressure combustor test facility was performed to ensure the desired increase in hydrogen consumption could be achieved. The experience, in addition to adaptations for field testing, was used to test and validate a new long term operational limit of 25% hydrogen content in the fuel. The success of the test campaign allows reduction in natural gas fuel consumption and cost, reduction in flaring of product waste gas, with a reduced power plant CO2 footprint. The development program and engine field testing substantiation are described in detail herein.
Alternative Aviation Fuels Evaluated for Lean-Flame NOx and Blowout, and Rich-Flame Soot Threshold
Authors: Hoseyni Chime Arshiya , Kalia Aman , Kramlich John , Novosselov Igor , Malte Philip C. , Vijlee Shazib
Published: August 2018

Alternative aviation fuels are evaluated for lean-flame NOx formation, lean-flame blowout (LFBO), and rich-flame soot threshold. The alternative aviation fuels evaluated are: hydro-processed renewable jet (HRJ) made from camelina and tallow, Fischer-Tropsch (FT) jet made from coal and natural gas, and alcohol-based jet. Chromatographic analysis (from another lab) shows that these fuels are composed mainly of iso-alkanes. These fuels are burned as received and with 10–20% aromatic added. For comparison, petroleum-based jet fuels are burned: JP5, JP8, Jet-A, and an aromatic blend. Additionally, we burn several pure fuels: n-hexane, cyclo-hexane, n-octane, iso-octane, n-dodecane, 1-3-5 tri-methyl benzene (TMB), and toluene. The NOx and blowout experiments are performed in a jet-stirred reactor (JSR), and the soot threshold experiments are performed on a Meker burner. The fuels are burned pre-vaporized, premixed, and preheated.

NOx is measured by probe sampling and chemiluminescent analysis at a fixed temperature for each fuel. Soot tendency is measured as the fuel-air equivalence ratio (phi) for the first appearance of yellow tips in the flame. This is termed the soot threshold. LFBO is examined by measuring the JSR temperature immediately prior to blowout.

Relatively small changes in NOx, LFBO, and soot threshold are measured for the petroleum-based and alternative jet fuels examined. HRJ-tallow is the cleanest burning jet fuel tested with respect to NOx and soot measurements. It exhibits the lowest NOx and the highest soot threshold among alternative fuels tested.

A possible correlation between decreasing NOx and increasing soot threshold is explored. The impact of adding aromatic content to the alternative jet fuels is also examined. With 20% aromatic content added to the alternative jet fuels, the soot threshold decreases, though the HRJ-tallow with 20% aromatic added continues to maintain a higher soot threshold than petroleum-based jet fuels. The addition of 20% aromatic does not show a clear trend in NOx. Over the four alternative jet fuels tested, the 20% aromatic addition causes a maximum change in the NOx emission of ± 13% (relative); the average change is close to zero.
Delamination Fracture in Ceramic Matrix Composites: From Coupons to Components
Authors: Kumar Rajesh S. , Mordasky Matthew , Ojard Greg
Published: August 2018

Delamination fracture can occur in complex-shaped Ceramic Matrix Composite (CMC) components due to a combination of high interlaminar stresses and low interlaminar strength and toughness. In this paper, delamination propagation in SiC-based CMC is studied using experiments and corresponding computational modeling. Room-temperature Double Cantilever Beam (DCB) testing was conducted to study mode I delamination propagation. Cohesive-zone finite element analyses were conducted to explain the experimental data and to extract delamination cohesive-zone parameters. The extracted parameters are then used to analyze a representative complex geometry and results compared against corresponding experimental data. It is shown that accurate modeling of the crack growth resistance behavior is essential for consistent modeling of delamination behavior ranging from simple coupons to complex sub-element/components.
Influence of Flow Coefficient on the Unsteady Impeller Loading Induced by the Impeller-Diffuser Interaction
Authors: Kong Dongjae , Song Seung Jin
Published: August 2018

Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulation has been conducted to investigate how flow coefficient affects unsteady impeller loading. Simulations have been carried out at three flow coefficients — near stall, design, and near choke conditions — for a radial gap of 1.04. For computational efficiency, the unsteady simulation has been conducted for two impeller and diffuser passages via Fourier Transformation method. Both steady and unsteady simulations have been validated against experimental data. The unsteady loading (the difference between the maximum and minimum loadings) is the largest at the near stall condition; second largest at the near choke condition; and smallest at the design condition. Flow coefficient effects on the unsteady impeller loading are mostly due to the variations in pressure fluctuations on the pressure side of the impeller blade. Relative to the design condition, the near stall condition shows lower minimum loading and the near choke condition shows higher maximum loading. Thus, both off design conditions result in higher unsteady loading than the design condition. Such differences stem from the variations in the pitch-wise static pressure at the diffuser vane inlet caused by the flow incidence onto the diffuser vanes.
Coupling Process Analysis on the Flow and Heat Transfer of Hydrocarbon Fuel With Pyrolysis and Pyrolytic Coking Under Supercritical Pressures
Authors: Zhao Chaofan , Hu Xizhuo , Zhu Jianqin , Tao Zhi
Published: August 2018

The regenerative cooling technology has become the most effective method to reduce the high-temperature of the scramjet engine. With physical and chemical heat sink, the endothermic hydrocarbon fuel has excellent performance in the regenerative cooling system of the scramjet engine which operates under extremely high temperature. The pyrolytic reactions not only absorb a large amount of heat, but also produce some kinds of coking precursors, mainly alkenes and aromatics. Because of the coking precursors and the coking reactions, a lot of coke would be generated on the wall and exert strong impact on the heat transfer, as the conductivity of the coke is much lower than that of the metal wall. Meanwhile, the surface coking changes the geometric parameters of the cooling tube, which leads to the flow field variations with the thickening coking layer. So, it is needed to find out the interaction between these variations. In this paper, a one-dimensional (1D) model has been developed to calculate the flow and heat transfer parameters distributions of the pyrolytically reacted RP-3 along the regenerative cooling tube with the pyrolytic coking. The 24-step pyrolytic reaction model and the coking kinetic model are applied to predict the pyrolysis and pyrolytic coking process of RP-3, with accurate computations of the physical properties of fluid mixture which undergo drastic variations during the transcritical process. Comparisons between the current predictions and the open published experimental data are carried out and good agreement is achieved. Calculations on the coupling relationships between the flow, heat transfer, pyrolysis and pyrolytic coking within 20 min in the circular tube have been conducted. With the heat flux increased, the coke mass is rising sharply and the temperature of the outer tube wall rises rapidly owing to the increasing thermal resistance of the coke layer. Moreover, the flow velocity becomes faster during the narrowing process of the tube caused by surface coking. In order to better understand the coking characteristics, further investigations on distributions of the surface coking under heat fluxes of 1.2–2.0MW/m2, pressures of 2.6–7.4 MPa and with inlet velocities of 0–5m/s have been performed. Results reveal that all these factors play an important role in the pyrolytic reactions and the coking rate distributions. The results in this paper have significant reference value in the design of the regenerative cooling system.
Development of High Specific Load and Low Mechanical Loss Journal Bearing With Two Pads of Tilting Supported Type
Authors: Nakano Takashi , Waki Yuichiro , Sumi Yuki , Yoshimine Chihiro , Yamawaki Teruaki
Published: August 2018

The demand for improving the steam turbine economic efficiency is being expected for both GTCC and conventional power plants. MHPS suggests HP/IP/LP separate casing and one bearing/rotor (one bearing between two casings) type steam turbine to enhance the turbine efficiency and reduce the cost of construction. Separate casing is preferable for blade aerodynamic performance, and one bearing/rotor is effective to reduce turbine bearing mechanical losses and turbine length. From the view point to design this type of rotor shaft arrangement, the most important point is to apply bearing technologies to permit the higher specific load and lower mechanical loss as well as for better dynamic oil film characteristics. The new two pads tilting journal bearing has been developed, utilizing MHPS’s experience on traditional two pads bearing with direct lubrication. The bearing structure and design parameters are optimized and good static and dynamic performance are obtained. Further, as practical countermeasures for a sub-synchronous vibration, the oil supply nozzle efficiency is improved, while properly adjusting supply oil flow distribution. The 610 mm size bearing test was conducted in-house test facility. The limit of specific load was verified, the bearing loss has become less than target.
Gas Turbine Fouling Offshore: Air Intake Filtration Optimization
Authors: Madsen Stian , Watvedt Jørn , Bakken Lars E.
Published: August 2018

Optimized operation of gas turbines is discussed for a fleet of eleven LM2500PE engines at a Statoil North Sea offshore field in Norway. Three engines are generator drivers while eight engines are compressor drivers. Several of the compressor drive engines run at peak load (T5.4 control), hence production rate is limited by the available power from these engines. The majority of the engines discussed run continuously without redundancy, hence gas turbine uptime is critical for the field’s production and economy. The performance and operational experience with upgraded inlet air filter systems, as well as successful operation at longer maintenance intervals and higher average engine performance are described.

For North Sea operation, a key property of the filter system is the ability to handle high humidity and high salt-content, typical of the harsh environment in these waters. The upgraded filter system analyzed in this paper is a 2-stage system (vane separator stage upstream of the high-efficiency filter stage), which is a simplified design versus the old traditional 3-stage systems (louvre upstream and vane separator downstream of the filter stage). These 2-stage systems rely on an efficient upstream vane separator to remove the vast majority of water from the airflow before it reaches the high-efficiency filters. The high-efficiency filters are specially designed to withstand moisture. The effectiveness and contribution of each component in the filtration system are described. Extensive testing of both new and used filter elements, of different filter grade and operated at different intervals, has been performed in a filter test rig facility onshore. Extensive testing of used filters has also been performed at the filter OEM, where filter efficiency is measured as well as destructive testing and analysis of the filter layers.

The effect of an optimized air intake filter system for the subject engines, is longer operating intervals, higher power availability and lower engine deterioration. The operating intervals are now extended to six months (4,000 hours), from initially two months (1,500 hours, early 1990s) then four months (3,000 hours, mid 2000s). The HPC efficiency deterioration is reduced by some 3% related to intake filter system, of a total of over 6% in efficiency deterioration over each 6-month operating period.
Impact of Upstream Boundary Conditions on Fuel Injector Performance in a Low TRL Reacting Flow Experimental Facility
Authors: Williams M. A. , Carrotte J. F. , Moran A. J. , Walker A. D.
Published: August 2018

It has been known for a sometime that the compressor exit profile can have a significant effect on the overall performance of the fuel injector. This effect has been increased recently with the advent of larger leaner injection systems. With a modern gas turbine combustion system the fuel injectors are presented with a non-uniform feed generated by the upstream compressor and OGV/pre-diffuser assembly. For generic lean burn combustion systems previous experimental and numerical work highlighted a complex interaction between the compressor efflux and the upstream diffuser. Circumferential non-uniformities in the flow presented to the fuel injector can amount up to ±10% of the mean velocity. Previous investigations examined only the isothermal flow field and the effects of this level of non-uniformity on reacting performance are not known. There are potential impacts on local fuel atomisation, air/fuel mixing and hence emissions performance.

The main aim of this paper is to observe and assess the effect of these upstream conditions using a reacting flow test facility. In the initial design phases reacting flow experiments are generally conducted in simple, single sector plenum fed test facilities. Since this does not capture the effects of non-uniformities modifications were made to the facility to produce an aerodynamically representative feed. CFD was used in the design process to ensure that the aerodynamic features present in engine geometries would be faithfully reproduced by the test rig modifications. The CFD also highlighted changes in the downstream isothermal flow field. This included differences in the overall effective area of the fuel injector and, importantly, a redistribution of mass flow between the various fuel injector passages. Additionally, the cone angle, and the flow structure downstream was observed to change.

Back-to-back tests were then conducted in a reacting flow test facility for various pilot-mains fuel flow splits and air-to-fuel ratios. Visualisation of the flame showed notable qualitative differences in the structure and stability of the flame. Quantitative measurements indicated that, compared to a plenum feed, a representative feed produced changes in the production of carbon monoxide, unburned hydrocarbons and oxides of nitrogen. Emission results were used to calculate the extent of the mass flow redistribution between passages. From this a correction was applied to the estimated AFRs. This correction did not fully collapse the emissions data, suggesting that while the mass flow redistribution contributes to the change in emissions it is not fully responsible. Covered in this paper are initial observations. However, further work is required to fully understand how the changes to the aerodynamic flow field alter the emissions performance, but it is clear that having a representative fuel injector feed is important in low TRL testing.
Prediction of Secondary Flow Features in a Low Pressure Turbine
Authors: Jonak Pawel , Borzecki Tomasz , Konopa Maciej , Kubacki Slawomir
Published: August 2018

A simulation of the flow through a four-stage low pressure turbine (LPT) of an aero-engine is performed using an eddy-viscosity based RANS model. An analysis of secondary flow details in the vicinity of endwalls and strut surface is performed. An interaction of wakes generated by the swirler vanes and end-wall boundary layers is also studied. The CFD results are compared with own test rig data of LPT obtained in Polonia Aero Lab in Zielonka (Poland). Global flow parameters were reproduced in good agreement with experiment (difference less than 1.5%). Satisfactory agreement between measured and predicted pressure distribution on the surface of inlet strut has been obtained.
Using Robust Design Methods for the Fir-Tree Optimization Problem
Authors: Vasilyev Boris , Salnikov Anton , Semenov Artem
Published: August 2018

The difficulty of providing the required strength characteristics of wheel locking joints is due to a complex stress state, the presence of stress concentrators, differences in contacting-part materials’ characteristics, and possible deviations in sizes from nominal values [1]. Providing stable strength characteristics and a low mass are important requirements. This paper suggests an approach to the strength-mass optimization of a disc and fir-tree joint of a high-pressure turbine and considers the scattering of dimensions within tolerances.

The main stages of optimization are shown, criteria for evaluating the robustness of the structure are proposed, and recommendations for the practical robust optimization of a real design are given. The results of various optimization approaches and strength-parameter dispersions of various configurations’ locking joints are compared. It is shown that decreasing the number of teeth increases the stability of the strength parameters.
An Experimental Investigation on Internal Flow Characteristics in a Realistic and Entire Coolant Channel With Ribs and Film Holes
Authors: Wang Peng , Pu Jian , Yu Ren-bin , Wang Jian-hua , Wan Bo , Luo Jian-Xia , Tian Shu-qing
Published: August 2018

This paper presents an experimental investigation on the flow characteristics within an entire coolant channel of a 2nd stage high pressure (HP) static turbine blade using TRPIV (Time-Resolution Particle Image Velocimetry) technique. The serpentine channel with three passages connected by a sharp bend, a round bend, 2 tip exits, 8 tailing exits and 40 film-holes staggered arranged on pressure side (PS) of the third pass is chosen as specimen, whose cross sections are manufactured to keep the real blade-shape. Ribs with a fixed spacing-to-height of 7 and an angle of 60° to the flow direction are applied on two opposite walls. The experiment is carried out at a fixed inlet Reynolds number of Rein = 23508. The variation process of secondary vortices and the main flow patterns in typical planes of the realistic coolant channel are successfully captured by TRPIV technique. The effects of rib, bend, cross-sectional shape, layout of passages, ejection ratio on the flow characteristics are analyzed and discussed. The following five new phenomena can be obtained. Namely, 1) near the two bend-regions, the rib can reduce the size of separation bubble and generate a new flow-acceleration downstream of the rib. 2) The rib-vortices combined with the mixing vortex caused by the bend and layout of channels, which leads to a new pair of vortices downstream of the bend, and further downstream, in the pair of vortices, the larger vortex presses the smaller vortex to form a new large vortex. This phenomenon has not been captured up to now in simplified ribbed two-pass channels and smooth realistic channels. 3)The development process of the secondary vortices and asymmetric behavior of main flow structure are similar in the regions of the sharp and round bends. 4)The coolant ejection from the tip exit in the sharp bend can decrease the mixing speed of the secondary vortices downstream of the bend. 5)The tip ejection from the trailing edge exits and film holes can reduce of the size of the secondary vortices downstream of the bend.
Numerical Investigation on Bearing Chamber Wall Heat Transfer
Authors: Tatar Volkan , Piskin Altug
Published: August 2018

Bearing chamber of a gas turbine engine is generally sealed by pressurized air, separating lubricant from the other zones of the engine. Heat transfer from the wall to air/oil mixture is a challenging engineering problem; predicting heat transfer rate from bearing chamber to oil is important to avoid oil coking and oil fires under high rotational speeds, pressure levels and turbine inlet temperatures. In this study, the inner wall temperature of bearing chamber which is located at the center of front engine structure was investigated numerically. The numerical study involved mainly two thermal modelling methods having two different empirical correlations was performed with finite element solver in order to calculate heat transfer on the wall. First method was based on rotational Reynolds number and Prantl number, in addition to these numbers second one, which is suggested in the literature, is based on oil related and sealing air related Reynolds number, mixture temperature and mixture mass flow. Second approach considers existence of a mixing of gaseous and liquid flow in the core flow unlike first modelling approach. The thermal model was solved by finite element solver and numerical model, assumptions were described with thermal boundary conditions. On the other hand, wall and air thermocouple readings were taken through engine test from the bearing chamber for real engine operating conditions having mainly idle, cruise and maximum power. DN number ranges from 712564 to 2742404, sealing air flow ranges from 46 to 78 g/s and oil flow ranges 22 to 40 g/s for these conditions. The calculated heat transfer coefficients were presented and discussed. The wall temperature predictions of the thermal models, and test measurements were compared. The comparison revealed that analysis results obtained with both correlations were in reasonable agreement with the test. In overall, the second approach predicted metal temperature slightly better at the front support and inner manifold wall, while first approach predicted much better at the rear support wall.
Review of Heated Sand Particle Deposition Models
Authors: Hsu Kwen , Barker Brett , Varney Bruce , Boulanger Andrew , Nguyen Vy , Ng Wing F.
Published: August 2018

Sand & dust ingestion is a critical issue for aero engines as the particles can deposit on surfaces in the hot sections of the engine. These deposits can block cooling holes, damage to components and alter the gas path geometry leading to performance loss and potentially power failure. A number of sand particle deposition models have been developed in recent years with the goal of developing a predictive tool for sand deposition. These models utilize different approaches for modeling the particle-surface physics and were developed using either purely material property theories or experimental data from different sources or both. Comparing these models can be difficult due to differences in material assumptions and different test cases. In this study, a CFD simulation was conducted of the Virginia Tech Aerothermal rig experiments and some selected depositions models were applied. The results were compared to each other and the rig results so that their accuracy, performance, and recommended improvements could be discussed.
Adjoint Method to Calculate the Shape Gradients of Failure Probabilities for Turbomachinery Components
Authors: Gottschalk Hanno , Saadi Mohamed , Doganay Onur Tanil , Klamroth Kathrin , Schmitz Sebastian
Published: August 2018

In the optimization of turbomachinery components, shape sensitivities for fluid dynamical objective functions have been used for a long time. As peak stress is not a differential functional of the shape, such highly efficient procedures so far have been missing for objective functionals that stem from mechanical integrity. This changes, if deterministic lifing criteria are replaced by probabilistic criteria, which have been introduced recently to the field of low cycle fatigue (LCF).

Here we present a finite element (FEA) based first discretize, then adjoin approach to the calculation of shape gradients (sensitivities) for the failure probability with regard to probabilistic LCF and apply it to simple and complex geometries, as e.g. a blisk geometry.

We review the computation of failure probabilities with a FEA postprocessor and sketch the computation of the relevant quantities for the adjoint method. We demonstrate high accuracy and computational efficiency of the adjoint method compared to finite difference schemes. We discuss implementation details for rotating components with cyclic boundary conditions. Finally, we shortly comment on future development steps and on potential applications in multi criteria optimization.
Assessment of Wall Modelling for Large Eddy Simulations of Turbomachinery
Authors: Movva Jagadeesh , Papadogiannis Dimitrios , Hiernaux Stéphane
Published: August 2018

The design process of turbomachinery components relies heavily on Reynods Averaged Navier Stokes (RANS) simulations. This approach is well suited for steady simulations and comes with a low computational cost. However, turbomachinery flows are complex and difficult to predict accurately with RANS computations. Large Eddy Simulations (LES), capable of resolving the larger scales of turbulence, are a promising way to improve the predictive capability of numerical simulations. The main drawback of LES for wall bounded flows is its high computational cost, scaling with Re1.86 [1]. Turbomachinery components are characterized by Re ≈ 105–6, implying simulations with several billions of cells, with most allocated to resolve the turbulent scales inside the boundary layers. A potential cost-reducing approach is to introduce wall modelling. However, several questions remain, notably the wall model interaction with the laminar-to-turbulent transition and the impact of grid resolution. To clarify these points we investigate the flow across a linear compressor cascade with Wall Resolved LES (WRLES) and Wall Modelled LES (WMLES) simulations. Various near-wall resolutions are tested at on and off-design conditions to characterize the impact of the wall model on the flow field and the aerodynamic losses. RANS simulations complement the analysis. The results indicate that the WRLES agree the closest with experimental measurements. WMLES with relatively high near-wall resolution capture most of the flow physics while allowing a significant speed-up. However, reducing the resolution further leads to unphysical flow separations, despite staying well in the range of wall model validity.
Detection of Strain and Damage Distribution in SiCf/SiC Mechanical Test Coupons
Authors: Newton Christopher D. , Jones J. Paul , Gale Louise , Bache Martin R.
Published: August 2018

The complex structural architecture and inherent processing artefacts within ceramic matrix composites combine to induce inhomogeneous deformation and damage prior to ultimate failure. Sophisticated mechanical characterisation is vital in support of a fundamental understanding of deformation in ceramic matrix composites. On the component scale, “damage tolerant” design and lifing philosophies depend upon laboratory assessments of macro-scale specimens, incorporating typical fibre architectures and matrix under representative stress-strain states.

Bulk measurements of strain via extensometry or even localised strain gauging will fail to characterise such inhomogeneity when performing conventional mechanical testing on laboratory scaled coupons. The current research project has, therefore, applied digital image correlation (DIC), electrical resistance monitoring and acoustic emission techniques to the room and high temperature assessment of a SiCf/SiC composite under axial fatigue loading.

Data from these separate monitoring techniques plus ancillary use of X-Ray computed tomography and optical inspection were correlated to monitor the onset and progression of damage during cyclic loading.
Erosion in Gas-Turbine Grade Ceramic Matrix Composites (CMCs)
Authors: Kedir N. , Gong C. , Sanchez L. , Presby M. J. , Kane S. , Faucett D. C. , Choi S. R.
Published: August 2018

Erosion behavior of a large number of gas-turbine grade ceramic matrix composites (CMCs) was assessed using fine to medium grain garnet erodents at velocities of 200 and 300 m/s at ambient temperature. The CMCs used in the current work were comprised of nine different SiC/SiCs, one SiC/C, one C/SiC, one SiC/MAS, and one oxide/oxide. Erosion damage was quantified with respect to erosion rate and the damage morphology was assessed via SEM and optical microscopy in conjunction with 3-D image mapping. The CMCs response to erosion appeared to be very complicated due to their architectural complexity, multiple material constituents, and presence of pores. Effects of architecture, material constituents, density, matrix hardness, and elastic modulus of the CMCs were taken into account and correlated to overall erosion behavior. The erosion of monolithic ceramics such as silicon carbide and silicon nitrides was also examined to gain a better understanding of the governing damage mechanisms for the CMC material systems used in this work.
Conceptual Flutter Analysis of Labyrinth Seals Using Analytical Models: Part II — Physical Interpretation
Authors: Vega Almudena , Corral Roque
Published: August 2018

A simple non-dimensional model to describe the flutter onset of labyrinth seals is presented. The linearized equations for a control volume which represents the inter-fin seal cavity, retaining the circumferential unsteady flow perturbations created by the seal vibration, are used. Firstly, the downstream fin is assumed to be choked, whereas in a second step the model is generalized for unchocked exit conditions. An analytical expression for the non-dimensional work-per-cycle is derived. It is concluded that the stability of a two-fin seal, depends on three non-dimensional parameters, which allow explaining seal flutter behaviour in a comprehensive fashion. These parameters account for the effect of the pressure ratio, the cavity geometry, the fin clearance, the nodal diameter, the fluid swirl velocity, the vibration frequency and the torsion center location in a compact and interrelated form. A number of conclusions have been drawn by means of a thorough examination of the work-per-cycle expression, also known as the stability parameter by other authors. It was found that the physics of the problem strongly depends on the non-dimensional acoustic frequency. When the discharge time of the seal cavity is much greater than the acoustic propagation time, the damping of the system is very small and the amplitude of the response at the resonance conditions is very high. The model not only provides a unified framework for the stability criteria derived by Ehrich [1] and Abbot [2], but delivers an explicit expression for the work-per-cycle of a two-fin rotating seal. All the existing and well established engineering trends are contained in the model, despite its simplicity. Finally, the effect of swirl in the fluid is included. It is found that the swirl of the fluid in the inter-fin cavity gives rise to a correction of the resonance frequency and shifts the stability region. The non-dimensionalization of the governing equations is an essential part of the method and it groups physical effects in a very compact form. Part I of the paper[3] detailed the derivation of the theoretical model and drew some preliminary conclusions. Part II analyzes in depth the implications of the model and outlines the extension to multiple cavity seals.
Towards Improved Boundary Layer Flashback Resistance of a 65 kW Gas Turbine With a Retrofittable Injector Concept
Authors: Kalantari Alireza , McDonell Vincent , Samuelsen Scott , Farhangi Shahram , Ayers Don
Published: August 2018

Lean premixed combustion is extensively used in gas turbine industry to reduce pollutant emissions. However, combustion stability still remains as a primary challenge associated with high hydrogen content fuels. Flashback is a crucial concern for designing gas turbine combustors in terms of operability limits. The current experimental study addresses the boundary layer flashback of hydrogen-air premixed jet flames at gas turbine premixer conditions (i.e. elevated pressure and temperature). Flashback propensity of a commercially available injector, originally designed for natural gas, is studied at different operating conditions and corresponding measurements are presented. The pressure dependence of flashback propensity is consistent with previous studies. The previously developed flashback model is successfully applied to the current data, verifying its utilization for various test conditions/setups. In addition, the model is used to predict flashback propensity of the injector at the actual engine preheat temperature. The injector is then modified to increase boundary layer flashback resistance and the corresponding data are collected at the same operating conditions. To avoid the boundary layer flashback, the mixture is leaned out in the near-wall region, where the flame can potentially propagate upstream. The comparison of gathered data shows a clear improvement in flashback resistance. This improvement is further elaborated by numerically studying fuel/air mixing characteristics for the two injectors.
Experimental Study of Periodic Free Stream Unsteadiness Effects on Discrete Hole Film Cooling in Two Geometries
Authors: Borup Daniel D. , Fan Danyang , Elkins Christopher J. , Eaton John K.
Published: August 2018

Discrete hole film cooling is widely employed to protect turbine blades and vanes from hot combustion gases entering the high-pressure turbine stage. Accurate prediction of the heat transfer near film cooling holes is critical, and high-fidelity experimental data sets are needed for validation of new computational models. Relatively few studies have examined the effects of periodic main flow unsteadiness resulting from the interaction of turbine blades and vanes, with a particular lack of data for shaped hole configurations. Periodic unsteadiness was generated in the main flow over a laidback, fan-shaped cooling hole at a Strouhal number (St = fD/U) of 0.014 by an airfoil oscillating in pitch. Magnetic Resonance Imaging (MRI) with water as the working fluid was used to obtain full-field, phase-resolved velocity and scalar concentration data. Operating conditions consisted of a hole Reynolds number of 2900, channel Reynolds number of 25,000, and blowing ratio of unity. Both mean and phase-resolved data are compared to previous measurements for the same hole geometry with steady main flow. Under unsteady freestream conditions, the flow separation pattern inside the hole was observed to change from an asymmetric separation bubble to two symmetric bubbles. The periodic unsteadiness was characterized by alternating periods of slow main flow, which allowed the coolant to penetrate into the freestream along the centerplane, and fast, hole-impinging main flow, which deflected coolant towards the laidback wall and caused ejection of coolant from the hole away from the centerplane. Mean adiabatic surface effectiveness was reduced up to 23% inside the hole, while mean laterally-averaged effectiveness outside the hole fell 28–36% over the entire measurement domain. A brief comparison to a round jet with and without unsteadiness is included; for the round jet, no disturbance was observed inside the hole, and some fluctuations directed coolant towards the wall, which increased mean film cooling effectiveness. The combined velocity and concentration data for both cases are suitable for quantitative validation of CFD predictions for film cooling flows with periodic freestream unsteadiness.
Planning for Successful Transients and Trips in a 1 MWe-Scale High-Temperature sCO2 Test Loop
Authors: Allison Timothy C. , Moore J. Jeffrey , Hofer Doug , Towler Meera Day , Thorp Joseph
Published: August 2018

Supercritical CO2 power cycles incorporate a unique combination of high fluid pressure, temperature, and density as well as limited component availability (e.g., high-temperature trip valves) that can result in operational challenges, particularly during off-design and transient operation. These conditions and various failure scenarios must be considered and addressed during the facility, component, and control system design phase in order to ensure machinery health and safety during operation. This paper discusses significant findings and resulting design/control requirements from a detailed failure modes and effects analysis that was performed for the 1 MWe-scale supercritical CO2 test loop at Southwest Research Institute, providing insight into design and control requirements for future test facilities and applications. The test loop incorporates a centrifugal pump, axial turboexpander, gas-fired primary heat exchanger, and micro-channel recuperator for testing in a simple recuperated cycle configuration at pressures and temperatures up to 255 bara and 715°C, respectively. The analysis considered offdesign operation as well as high-impact failures of turbomachinery and loop components that may require fast shutdowns and blowdowns. The balance between fast shutdowns/blowdowns and the need to manage thermal stresses in the turbomachinery resulted in staged shutdown sequences and impacted the design/control strategies for major loop components and ancillary systems including the fill, vent, and seal supply systems.
Experimental and Numerical Study of Critical Flow Model Development for Supercritical CO2 Power Cycle Application
Authors: Kim Min Seok , Oh Bong Seong , Jung Hwa-Young , Bae Seong Jun , Lee Jeong Ik
Published: August 2018

Supercritical CO2 (S-CO2) has the potential to be used as the working fluid in a power cycle since S-CO2 shows a density value high as its liquid phase while the viscosity value remains closer to its gaseous phase. Thus, it requires much less work to compress due to its low compressibility as well as relatively small flow resistance. However, the S-CO2 leakage flow from turbo-machinery via seal becomes one of the important issues since not only it influences the cycle efficiency due to parasitic loss but also it is important for evaluating the system safety under various operating conditions.

In the previous turbo expo paper, the effect of the tooth length on the critical flow and comparing the results to the existing two phase system analysis code calculation were presented. In this paper, the gap effect, which is simulated by changing the diameter of a orifice and the number of tooth effect in a labyrinth seal geometry nozzle are presented by using the same experimental facility described in the previous paper. In addition, this paper includes the experimental results under various conditions including not only single phase flow such as supercritical, and gaseous state only but also two phase flow condition.
The Influence of Geometry Deformation on a Multistage Compressor
Authors: Teng Xin , Chu WuLi , Zhang HaoGuang , Liu Kai , Li JinGe
Published: August 2018

Over the service time, the rotating parts of turbine engine vary in their geometry. When aircraft take off or fly through a volcanic ash cloud, the particles are sucked into the engine, impinge the blade and gradually erode the surface. The impinging between particles and blades is responsible for the increase of the surface roughness. Also, during the long-time operation, the function of the blade’s stacking law combined with the centrifugal force could cause deviation of the stagger angle. Moreover, blade tip clearance could vary because of the casing deformation. All the deformation of geometry could severely reduce the engine performance and thus engine life.

The work presented in this paper focused on the influence of geometry deformation in a real low-pressure compressor. The investigation is more difficult than most of the previously published researches with a total of five stages being considered. Due to the irregularities in geometry, it is difficult to numerically assess the performance of the compressor. The aim of this study is to give an analysis method that allows an efficient and accurate estimation of the performance for multistage compressor with geometry deformation. In the first step, the geometry models with different deviation in tip clearance, roughness and stagger angle were established respectively. A CFD study was then applied to the compressor with RANS method to calculate the flow field with different types of deformation. The variation of overall performance due to the deformation was finally analyzed to identify the dominant factor on influencing the performance of the compressor among different types of geometry deformation. A method based on polytropic efficiency analysis and flow field analysis was also established to specifically analyze which stage is most sensitive to the geometry deformation.

The results show a significant influence of geometric deformation on the efficiency, total pressure rise and flow range of the multistage compressor. The conclusions of this study would provide an important guidance for engine overhaul in the factory.
Study on the Performance Variation of Compressor Under Salt Fog Scale
Authors: Sun HaiOu , Wang Lisong , Wan Lei , Qu Feng
Published: August 2018

Compressors are crucial to the efficient operation of a gas turbine; however, fouling, caused by adherence of particles to surfaces, can have a negative effect on compressor performance. In this study, a NASA Stage 35 single-stage axial-flow compressor was employed as the model for numerical simulation using the ANSYS CFX software of the effects caused by mild and severe fouling under salt fog scale. To measure these effects, two distinct models were used. For mild fouling, the simulated stator blade surface roughness was altered nonuniformly; for severe fouling, the simulated stator blade thick-ness was altered. Results indicated that surface roughness caused by mild fouling only has a small effect on compressor performance and no effect on the stable working range. However, changes in the blade thickness as a result of severe fouling have a large effect on compressor performance and a clear effect on the stability of the compressor’s working range. The fouling causes an increase in the boundary layer at the trailing edge of the suction side of the blade thereby increasing the loss of flow; fouling effect after emergence angle, wide design value, and increasing blade of circumferential stress.
Advanced Film Cooling Performance of a Y-Shaped Hole With Inner Crossflow
Authors: Luo Jianxia , Liu Cunliang , Zhu Huiren
Published: August 2018

Film cooling performances of three film holes have been numerical researched in this paper, including a lateral inclined cylindrical hole, a fan-shaped hole and a y-shaped hole. The simulation is computed by the commercial software Fluent based on Reynolds Averaged Navier-Stokes (RANS) equations and realizable k-ε turbulence model with enhanced wall treatment.

The y-shaped hole is a novel film hole developed from the lateral inclined cylindrical hole. With inner crossflow, the jet of the lateral inclined cylindrical hole performs to be two streams as a result of the helical motion in the hole. Accordingly, the hole exit was optimized with two expansions: one is expanded along the lateral inclined direction and the other is expanded along the mainstream flow direction. The lateral inclined cylindrical hole with two expansions at the exit is named the y-shaped hole. Compared to the fundamental lateral inclined cylindrical hole, the y-shaped hole has different counter-rotating vortices and much better film coverage.

Experiments have been conducted to test the film cooling performance of the y-shaped hole. Compared to the lateral inclined cylindrical hole, much higher film cooling effectiveness has been measured in the y-shaped hole as a result of the enhanced lateral film coverage and the weakened film dissipation in the streamwise direction. The film performance of the y-shaped hole rises with the increase of the blowing ratio. At M = 2.0, the film of the y-shaped hole keeps close to the wall while the film of the lateral inclined cylindrical hole is completely lifted up, resulting in the increase of the area average film cooling effectiveness up to 128.7%.