bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy Innovation: A Focus on Power Generation Data Capture and Analytics in a Competitive Market
Authors: Della Villa Salvatore A.
Published: August 2018

Efficiency, operational flexibility, durability, environmental friendliness, and reliability — these words are often used to define expectations and requirements for product performance, required in the energy market today. Yet, depending on where one looks at the curve of product evolution, these words have very different meanings. One thing remains constant, irrespective of where one looks at performance growth over time, product improvement requires actual field experience data on a number of operating plants and units, to supplement the testing and verification processes of the Original Equipment Manufacturer (OEM). The combination of the field experience with the latest testing, verification, and quality control techniques, followed by the OEM, is essential to achieve the inherent reliability and ultimately, the life-time expectations set by the market.

There is always a question as to the amount of actual field experience data that is necessary to validate product improvement or advancement. Today, the market seems to accept a lower standard of operating time (∼ 8,000 Actual Operating Hours (AOH)), compared with the past (∼ 100,000 AOH) for product validation. If Equivalent Operating Hours (EOH) were the basis for assessing the maturity of a new technology, the times would be lower. Whether the number is 8,000 or 100,000 AOH, the fact is that field experience data represents the intersection of the OEM’s design, validated through component and system level testing, coupled with the actual operating and maintenance practice and experience of the owner/operator. It is here that the OEM and owner/operator begin to directly share a common objective; the ability to demonstrate the efficiency, operational flexibility, durability, environmental friendliness and reliability of the product improvement. Consequently, the OEM and the owner/operator have a strong and shared interest in the accuracy, fidelity, and the completeness of field data; to ensure that an effective Failure Reporting and Corrective Action (FRACA) process is in place — driving continuous product improvement; to meet market expectations for equipment performance, and to support new product introduction.

The focus of this paper is field experience data, past and present, with a specific emphasis on the increasing influence and value that data has in the ever changing and competitive energy market. The paper will suggest that the present and future need for high fidelity equipment data (at a component level of detail) is not just essential for supporting engineering efforts for product evolution, but also to support effective Operations & Maintenance (O&M) strategies. The paper will advance the notion that the fusion of total plant data, from three primary sources, with the ability to transform, analyze, and act based on integrating subject matter expertise is essential for effectively managing assets for optimum performance and profitability; executing and delivering on the promise of “Big Data” and advanced analytics.
Development of High-Temperature High-Velocity Sand Erosion Apparatus
Authors: Suzuki Masaya , Yamane Takashi
Published: August 2018

Sand erosion due to gas-solid two-phase flow at high temperature and high velocity is an important issue in the lifetime of turbine vanes and blades in jet engines. In order to understand particulate erosion phenomena, a test apparatus was developed and sand erosion tests were conducted. The particle velocity was measured by particle image velocimetry and specimens’ surface temperatures were obtained using infrared thermal imaging and a thermocouple. The eroded surface geometry was investigated using a laser profiler. This paper presents the results of tests employing high-velocity and high-temperature gas-solid two-phase flow impinging on a flat plate at several angles.
Hybrid RANS-LES for Turbomachinery
Authors: Jefferson-Loveday Richard J.
Published: August 2018

A range of popular hybrid Reynolds averaged Navier-Stokes - large eddy simulation (RANS-LES) methods are tested for cavity and labyrinth seal flows using an in-house high-order computational fluid dynamics (CFD) code and a commercial CFD code. The models include the Spalart-Allmaras (SA) and Menter SST variants of delayed detached eddy simulation (DDES), the Menter scale adaptive simulation (SAS) model, and a new enhanced variant of SA-DDES recently presented in the literature. The latter modifies the original definition of the subgrid length-scale used in DDES based on local vorticity and strain. For both geometries, the meshes are hybrid RANS-LES adequate. Very low levels of resolved turbulent content are observed for both the cavity and labyrinth seal flows for all models apart from the enhanced version of DDES. Similar findings are observed for both the commercial and in-house CFD codes. For both cases most models essentially produce a quasi-two-dimensional flow field with minimal resolved content. For the cavity simulations there is a significant under prediction of turbulent statistics. The enhanced version of SA-DDES shows a significant improvement and resolves turbulent content over a wide range of scales. Improved agreement with experimental measurements is also observed. It is recommended that extreme care should be taken where hybrid RANS-LES simulations are essentially steady but have lower than RANS levels of eddy viscosity.
Transient Performance of Separated Flows: Characterization and Active Flow Control
Authors: Saavedra J. , Paniagua G.
Published: August 2018

The aerothermal performance of the low pressure turbine in UAVs’ is significantly abated at high altitude, due to boundary layer separation. During past years different flow control strategies have been proposed to prevent boundary layer separation, such as dielectric barrier discharges, synthetic jets, vortex generators. However, the optimization of the control approach requires a better characterization of the separated regions at several frequencies. The present investigation analyzes the behavior of separated flows, and specifically reports the inception, reattachment and separation length, that allows the development of more efficient methods to manipulate flow separation under non-tempo-rally uniform inlet conditions. The development of separated flows under sudden flow accelerations or pulsating inlet conditions were investigated with series of numerical simulations including Unsteady Reynolds Average Navier Stokes and Large Eddy Simulations. The present research was performed on a wall mounted hump, which imposes an adverse pressure gradient representative of the suction side of low pressure turbines. The heat transfer and wall shear stresses were fully documented, as well as the flow velocity and temperature profiles at different axial locations to characterize the near wall flow properties and the thermal boundary layer. Through a sudden flow acceleration we looked into the dynamic response of the shear layer detachment as it is modulated by the mean flow evolution. Similarly, we studied the behavior of the recirculation bubble under periodic disturbances imposed by sinusoidal inlet total pressure signals at various frequencies ranging from 10 to 500 Hz. During each period the Reynolds number oscillates between 40000 and 180000 (based on a characteristic length of 0.1 m). Finally, as a first step into the flow control approach we added a slot in our geometry to allow flow injection and ingestion just upstream of the separation inception. Exploring the behavior of the separated region at different slot pressure conditions we defined the envelope for its periodic actuation. Thanks to that analysis, we found that matching the actuator frequency with the frequency response of the separated region the performance of the actuation is boosted.
An Assessment on the Benefits of Additive Manufacturing Regarding New Swirler Geometries for Gas Turbine Burners
Authors: Giuliani Fabrice , Paulitsch Nina , Cozzi Daniele , Görtler Michael , Andracher Lukas
Published: August 2018

In the near future, combustion engineers will shape the burner according to the flame, and not the opposite way anymore. In this contribution, this idea is explored with the help of additive manufacturing (AM). The focus is put on the design and the production of swirlers using advanced materials with the least possible efforts in terms of manufacturing. The material chosen for this study is Inconel 718. There are three motivations to this project. The first one is to design new shapes and assess these in comparison to conventional ones. The second motivation is to be able to manufacture them using additive manufacturing, and to gather know-how on selective laser melting. The third motivation is to elaborate a methodology involving engineering, research and education to promote — only if and when this is desirable — the production of series of premium parts such as high-end components of gas turbine combustor using AM. First-of-a-kind swirler shapes are explained and designed. These are unlikely to be produced using conventional manufacturing. They are then successfully produced in Inconel 718 using AM. The raw parts are directly submitted for testing with no surface post-processing. The paper states why at current state-of-the-art the raw surface quality still needs improvement, and highlights the benefits of the new swirler shape versus conventional.
Modeling Near Critical and Supercritical Fuel Injection and Mixing in Gas Turbine Applications
Authors: Lettieri C. , Subashki G. , Spakovszky Z.
Published: August 2018

This paper presents a numerical framework for characterizing fuel injection in modern combustors. The approach utilizes scaling analysis to describe the droplet evaporation in non-dimensional and fluid-independent terms. The results of the model are validated against published experimental data of isolated droplets evaporating at subcritical and near-critical conditions. The model is incorporated in a spray calculation framework and extended to the supercritical regime to assess the impact of different fluid-properties and evaporation models on temperature and fuel vapor distributions.

The results suggest that in a non-convective environment the transient and quasi-steady evaporation rates vary exponentially with Lewis number. Furthermore, the results show fluid-independent behavior of the droplet evaporation, indicating that a single-component fluid can potentially be used as a modeling surrogate for jet fuel. The first-principles analysis demonstrates that classical evaporation models overestimate transient evaporation and underestimate quasi-steady evaporation, with discrepancies up to 70% at supercritical conditions. This is due to limitations in fuel-property description and the lack of non-isothermal droplet characterization at near-critical conditions. The temperature profiles are typically under-predicted and fuel vapor concentrations are over-predicted in standard spray calculations with subcritical evaporation models. As such the proposed framework breaks new ground in modeling of supercritical fuel injection. The improved quality in the predicted fuel concentration and temperature distribution can enable more accurate assessment of flame position, improving the estimation of combustion stability margins and NOx emissions. The model can be incorporated in commercial codes to guide the design of combustors operating at supercritical conditions.
Tomographic PIV in the Near Field of a Swirl-Stabilised Fuel Injector
Authors: Spencer Adrian , Brend Mark , Butcher Daniel , Dunham David , Cheng Liangta , Hollis Dave
Published: August 2018

The isothermal flow fields of injectors have undergone several computational and experimental investigations using point and planar measurement techniques,. Within the swirl induced vortex breakdown region it is only LES that has been able to predict fully the presence of a three dimensional helical vortex structure for a particular injector, and in certain conditions (no central fuel jet), a precessing vortex core. These structures can be elucidated from point and planar measurements and favorable comparisons of velocity statistics between experiment and LES predictions strengthen these findings. However, volumetric, 3-component measurement of velocity data has not been widely available to provide conclusive evidence of the exact three dimensional nature of the vortex structures that exist.

An experimental setup utilizing time resolved tomographic PIV on a water flow rig is described in this paper. This is used to provide as high-quality aerodynamic study as possible of a single stream radially-fed air swirl gaseous fuel injector. The level of accuracy of the tomographic PIV technique is demonstrated by calculating the divergence of the velocity field as well as validating the results against a comprehensive 2 and 3 component standard PIV velocity database and other measurement techniques and predictions.

Structure identification methods have been employed to visualise and understand the complex flow topology within the near field of the injector. The change in topology with and without the stabilising central jet is further investigated and agrees with findings of planar PIV results. While the velocity error associated with the tomo-PIV results is higher than the planar results the data agree well within the identified uncertainty bounds and are complimentary in understanding the flow field structure. Thus a full volumetric aerodynamic survey is available for the first time on this isothermal flow case.
Machine Learning for Alloy Composition and Process Optimization
Authors: Ling Julia , Antono Erin , Bajaj Saurabh , Paradiso Sean , Hutchinson Maxwell , Meredig Bryce , Gibbons Brenna M.
Published: August 2018

The drive for greater efficiency in turbomachinery has led to increasingly stringent specifications for the materials used. Current methods for optimizing alloy composition and processing to meet these requirements typically rely on a combination of expert judgment and trial and error. Machine learning offers an alternative approach that leverages data resources to significantly accelerate the optimization timeline through systematic data-informed decision making. In this paper, we demonstrate the effectiveness of machine learning methods for three different alloys classes: aluminum alloys, nickel-based superalloys, and shape memory alloys. In the first two alloy classes, models are built for the alloy mechanical properties based on the composition and processing information. In the case of shape memory alloys, a model is trained to predict the austenite to marten-site transformation temperatures. In addition to achieving high baseline performance, we leverage recent methodological developments to provide well-calibrated, heteroscedastic uncertainty estimates with each prediction. By wrapping these models in an inverse design routine that takes full advantage of uncertainty information, we are able to demonstrate the feasibility of designing new alloys to meet prescribed specifications. The results indicate that this approach has the potential to fundamentally change how new structural and functional alloys are developed.
Transient Characteristics of a Dual-Rotor System With Intershaft Bearing Subjected to Mass Unbalance and Base Motions During Start-Up
Authors: Chen Xi , Liao Mingfu
Published: August 2018

Using Newmark-Hilber-Hughes-Taylor (Newmark-HHT) integration method, transient characteristics of the dual-rotor system with an intershaft bearing subjected to mass unbalance and base motions during start-up are illustrated. Rotary inertia, gyroscopic moment, shear deformation, mass unbalance and deterministic base motions are considered. Due to variable angular velocities, additional stiffness matrices associated with rotating angular accelerations are also introduced in the equations of motion. The effects of base motion parameters on the dynamic characteristics of the dual-rotor system are discussed, including base axial rotation, lateral rotations, and harmonic translations.

The results show that base axial rotation significantly changes the transient critical speeds and resonant amplitudes of the dual-rotor system. In the case of base lateral rotation, the center of the orbit is no longer on the bearing centerline, but with a dynamic offset. When increasing the rotating speeds, the dynamic offset becomes greater. Unlike base lateral rotation, base harmonic translation doesn’t result in dynamic offset, but it amplifies response amplitudes over the entire range of rotating speed. In conclusion, it provides a flexible approach with high efficiency and good expandability to predict transient responses of dual-rotor systems under base motions, and to prevent dual-rotor systems against potential excessive vibration in the design phase.
Application of the Modal Approach for Prediction of Forced Response Amplitudes for Fan Blades
Authors: Eichner Franziska , Belz Joachim
Published: August 2018

Forced response is the main reason for high cycle fatigue in turbomachinery. Not all resonance points in the operating range can be avoided especially for low order excitation. For highly flexible CFRP fans an accurate calculation of vibration amplitudes is required.

Forced response analyses were performed for blade row interaction and boundary layer ingestion. The resonance points considered were identified in the Campbell diagram. Forced response amplitudes were calculated using a modal approach and results are compared to the widely used energy method. For the unsteady simulations a time-linearised URANS method was applied. If only the resonant mode was considered the forced response amplitude from the modal approach was confirmed with the energy method. Thereby forced response due to BLI showed higher vibration amplitudes than for blade row interaction.

The impact of modes which are not in resonant to the total deformation were investigated by using the modal approach, which so far, only considers one excitation order. A doubling of vibrational amplitude was shown in the case of blade row interaction for higher rotational speeds. The first and third mode-shape as well as modes with similar natural frequencies were identified as critical cases.

The behaviour in the vicinity of resonance shows high vibration amplitudes over a larger frequency range. This is also valid for high modes with many nodal diameters, which have a greater risk of critical strain.
Steam Turbine Exhaust Optimization Based on Gaussian Covariance Networks Using Transient CFD Simulations
Authors: Cremanns Kevin , Roos Dirk , Penkner Andreas , Hecker Simon , Musch Christian
Published: August 2018

Renewable energies are increasingly contributing to the overall volume of the electricity grid and demand besides high efficiency, greater flexibility of the conventional fossil power plants. To optimize these objectives, extensive CFD calculations are required in most cases. For example, transient CFD calculations are only rarely combined with an optimizer because of their high demand on computational resources and time. Surrogate models, which are mathematical methods to learn and approximate the relationship between input and output parameters, are a common way to solve these problems. Once they are trained, they can perform the evaluations within seconds and replace the expensive simulation. Of course, real calculations are still needed to generate the training data. Therefore, it is useful to apply efficient and sequentially extensible design plans.

This paper presents a new surrogate model method, based on a deep neural network learning the non-stationary hyperparameters of combined Gaussian process covariance matrices. It is used to approximate the complex and time consuming transient CFD simulation of a combined high-intermediate pressure steam turbine double shell outer casing. To minimize the exergy loss, the exhaust geometry is optimized in a single and multi-objective optimization on the surrogate models. The multi-objective optimization also includes the uniform velocity distribution of the steam in different areas of the casing, to predict the thermal loading of the steam turbine inner casing and to avoid an imbalanced thermal loading. A sequential sampling approach combined with a sensitivity analysis is used to find the minimum number of samples needed to train the surrogate models in order to gain sufficient prediction quality.

Additionally, the paper describes the initial geometry, its numerical setup and the required control mechanisms to avoid noisy designs, which might complicate the surrogate model training. There is also a comparison of the initial and chosen optimal designs.
Unsteady Computation of Ingress Through Turbine Rim Seals
Authors: Horwood Joshua T. M. , Hualca Fabian P. , Wilson Mike , Scobie James A. , Sangan Carl M. , Lock Gary D.
Published: August 2018

In high-pressure turbines, cool air is purged through rim seals at the periphery of wheel-spaces between the stator and rotor discs. The purge suppresses the ingress of hot gas from the annulus but superfluous use is inefficient. In this paper the interaction between the ingress, purge and mainstream flow is studied using unsteady numerical simulations based on the DLR TRACE solver. The computations are compared to experimental measurements from a one-and-a-half stage axial-turbine rig operating with engine-representative blade and vane geometries, and overlapping rim seals. Radial traverses using a miniature CO2 concentration probe quantified the penetration of ingress into the rim seal and the outer portion of the wheel-space. Unsteady pressure measurements from circumferentially-positioned transducers on the stator disc identified distinct frequencies in the wheel-space, and the computations reveal these are associated with large-scale flow structures near the outer periphery rotating at just less than the disc speed. It is hypothesised that the physical origin of such phenomenon is driven by Kelvin-Helmholtz instabilities caused by the tangential shear between the annulus and egress flows, as also postulated by previous authors. The presence and intensity of these rotating structures are strongly dependent on the purge flow rate. While there is general qualitative agreement between experiment and computation, it is speculated that the under-prediction by the computations of the measured levels of ingress is caused by deficiencies in the turbulence modelling.
Comparative Experimental Investigation of Leading Edge Cooling Concepts of Turbine Rotor Blades
Authors: Elfner Maximilian , Schulz Achmed , Bauer Hans-Jörg , Lehmann Knut
Published: August 2018

This paper presents extensive results of an ongoing study on internal blade cooling concepts. A new test rig has been designed, built and commissioned, allowing fast comparison of different cooling schemes as well as surface temperature measurements for different cooling concepts. By scaling the test specimen, full aerothermal similarity was achieved at high measurement accuracy and resolution. Surface temperature (and thus total cooling effectiveness) is measured using high resolution, high dynamic range infrared thermography with an improved data evaluation method.

Results for a conventional multi-pass cooling design are presented as a baseline case. Several new internal cooling concepts are then assessed for their relative cooling performance to the conventional design as well as their absolute cooling effectiveness. Those designs include various internal swirl concepts (cyclone cooling). The results show that great care has to be taken when designing advanced internal cooling concepts with complex flow structures, since the effects of internal crossflow, internal pressure loss, internal heat transfer coefficient, and film cooling effectiveness strongly interact with each other and the hot gas flow and hence affect the resulting total cooling effectiveness.
Robust Method to Solve Meanline Equations for Choked Flows
Authors: Cadrecha David , Chaquet Jose M. , Corral Roque , Timon Vicente P.
Published: August 2018

Although a meanline code solves simple algebraic equations, some difficulties arise in flows near choked condition. Using simplified 0-dimensional (0D) models, it is shown which flow variable drives this phenomena (total or meridional Mach number) depending on the boundary conditions. It is commented as well how the choked condition is modified depending on the loss coefficient used. Then, a novel numerical method based on a bisection approach is proposed to solve meanline equations. A simple method to enlarge speed lines obtained by the mean-line solver is also described. Finally, the performance map of a single-stage axial compressor is computed and compared with experimental data to show the capabilities of the proposed approach.
Soot Prediction in an Aircraft Combustor at Realistic Operation Conditions
Authors: Steinbach Alexander , Dittmann Tobias , Gerlinger Peter , Aigner Manfred , Eggels Ruud
Published: August 2018

This article presents numerical simulations of the Rolls-Royce BR700 combustor operating at various realistic conditions. Emphasis is put on the prediction of soot emissions. Three-dimensional steady Reynolds-averaged Navier-Stokes (RANS) simulations were performed employing the kϵ-model for turbulence closure. Combustion is modelled by finterate chemistry and the turbulence-chemistry interactions are captured by an APDF-approach (assumed probability density function) for temperature fluctuations. The injection of the liquid fuel Jet A-1 is described by a spray model applying Lagrangian methods for spray transport and atomization. The multi-component fuel is modelled as surrogate of n-decane, iso-octane and toluene. Reaction kinetics are described by a detailed mechanism, which is optimised for Jet A-1 oxidation and accurately resolves the reaction paths up to the smallest aromatic soot precursors benzene and toluene. Heavier PAHs (Polycyclic Aromatic Hydrocarbons) are lumped to sections and hence, modelled by a sectional approach, which leads to soot nucleation. The soot particle dynamics are described by a two equation model. Due to the model’s efficiency feasible computational costs are realised. Overall, four operation points are investigated, which are take-off, climb, approach and taxi. The simulation results at the combustor exit are compared to the experimentally determined Smoke Number of the engine exhaust gas by means of empirical correlations. The comparison shows a very good agreement. In particular, the Smoke Number’s trend is predicted well with respect to the thrust of the operation points.
Heat Recovery From a Liquefied Natural Gas Production Process by Means of an Organic Rankine Cycle
Authors: Ancona M. A. , Bianchi M. , Branchini L. , De Pascale A. , Melino F. , Ottaviano S. , Peretto A. , Scarponi L. B.
Published: August 2018

In the last years, the increased demand of the energy market has led to the increasing penetration of renewable energies in order to achieve the primary energy supply. However, natural gas is expected to still play a key role in the energy market, since its environmental impact is lower than other fossil fuels. It is mainly employed as gaseous fuel for stationary energy generation, but also as liquefied fuel, as an alternative to the diesel fuel, in vehicular applications.

Liquefied Natural Gas is currently produced mainly in large plants directly located at the extraction sites and transported by ships or tracks to the final users. In order to avoid costs and environmental related impact, in previous studies Authors developed a new plant configuration for liquefied natural gas production directly at filling stations. One of the main issues of the process is that in various sections the working fluid needs to be cooled by external fluids (such as air for compressor inter and after-cooling or chilling fluids), in order to increase the global performances. As a consequence, an important amount of heat could be potentially recovered from this Liquefied Natural Gas production process. Thus, based on the obtained results, in this study the integration between the liquefaction process and an organic Rankine cycle is proposed. In fact, the heat recovered from the Liquefied Natural Gas production process can be used as hot source within the organic Rankine cycle.

The aim of the work is the identification of the optimal integrated configuration, in order to maximize the heat recovery and, as a consequence, to optimize the process efficiency. With this purpose, in this study different configurations — in terms of considered organic fluid, architecture and origin of the recovered heat — have been defined and analyzed by means of a commercial software. This software is able to thermodynamically evaluate the proposed process and had allowed to define the optimal solution.
Robust Optimization Design of Single-Stage Transonic Axial Compressor Considering the Manufacturing Uncertainties
Authors: Li Zhihui , Liu Yanming , Agarwal Ramesh K.
Published: August 2018

Manufacturing uncertainties always lead to significant variability in compressor performance. In this work, the tip clearance uncertainties inherent in a transonic axial compressor are quantified to determine their effect on performance. The validated tip clearance losses model in conjunction with the 3D reynolds averaged navier-stokes (RANS) solver are utilized to simulate these uncertainties and quantify their effect on the adiabatic efficiency, total pressure ratio and choked mass flow. The sensitivity analysis method is employed to figure out which parameters play the most significant roles in determining the overall performance of compressor. To propagate these uncertainty factors, the non-intrusive polynomial chaos expansion (PCE) algorithm is used in this paper and the probability distributions of compressor performance are successfully predicted. A robust design optimization has been carried out based on the combination of the genetic algorithm (GA) and the uncertainty quantification (UQ) method, leading to a robust compressor rotor design for which the overall performance is relatively insensitive to variability in tip clearance without reducing the sources of the manufacturing noise. The optimization results show that the mean value of the adiabatic rotor efficiency is improved by 1.4 points with the overall variation of that reduced by 64.1%, while the total pressure ratio is slightly improved when compared to the prototype.
Investigation of Extinction and Reignition Events Using the Flamelet Generated Manifold Model
Authors: Elasrag Hossam , Li Shaoping
Published: August 2018

Simulations for the Cambridge swirl bluff-body spray burner are performed near blow-out conditions. A hybrid stress blended eddy simulation (SBES) model is utilized for sub-grid turbulence closure. SBES blends the RANS-SST model at the boundary layer with large eddy simulation dynamic Smagorinsky model outside the boundary layer. The injected N-heptane spray droplets are tracked using a typical Eulerian-Lagrangian approach. Heat transfer coupling between the bluff-body walls and the near-walls fluid is accounted for by coupling the solid and fluid energy equations at the bluff-body surface. Mixing and chemistry are modeled using the Flamelet Generated Manifold (FGM) model. The study investigates how successful the FGM model is in predicting finite rate effects like local extinction and flame lift-off height. To this end, two near blow-out spray flames, the H1S1 (75% to blow-out) and H1S2 (88% to blow-out) are simulated. Good results are shown matching the spray Sauter mean diameter (SMD) and axial velocity mean and rms experimental data. The results also show that the FGM model captured reasonably well the flame structure and lift-off height as well as the spray pattern. Overall the spray droplets mean D32 and mean axial velocity were under-predicted, while the rms distribution matched reasonably well for the H1S1 flame. The mean flame brush lift-off height is estimated based on the statistically stationary mean flame brush and is estimated to be around 6 mm from the bluff-body base. Instantaneous local flame extinction is observed. The H1S2 flame, however, showed similar but slightly better match with the measurements for the mean spray data compared to the H1S1 flame, with slight under-prediction for D32 at Z = 10 mm and Z = 20 mm. Future work will investigate the sensitivity of the simulation to the spray boundary conditions and grid resolution.
Effects of Impinging Hole Shapes on Double Swirl Cooling Performance at Gas Turbine Blade Leading Edge
Authors: Zhou Junfei , Wang Xinjun , Li Jun , Zheng Daren
Published: August 2018

A double swirl cooling method has been raised recently to enhance the internal cooling performance at the blade leading edge. This paper mainly focuses on investigating the flow and heat transfer characteristics of the double swirl cooling method. Further more, four kinds of elliptical holes are applied to show effects of impinging hole shapes on the cooling performance. Results of all double swirl cooling cases are compared with that of an impingement cooling structure under four Reynolds numbers. Overall averaged Nusselt number, friction factor and thermal performance factor are compared in all cases, Vortexes induced by different impinging hole types and target chambers are studied and compared. The spanwise averaged Nusselt number, Nusselt number contours and Nusselt number distributions at several cross sections are studied and compared. Results show that the double swirl cooling method can significantly enhance the heat transfer performance compared with the traditional impingement cooling structure. Double swirl cooling with cylindrical impinging hole shows the best thermal performance and lowest flow losses. By applying the elliptical impinging hole with the sharp side faced the mainstream flow direction and a larger major to minor axis length ratio, the rotational vortex inside the double swirl chamber can be better developed and the heat transfer performance is also promoted.
CFD Leakage Predictions of Labyrinth Seals Having Straight and Inclined Notched Teeth With Staggered Honeycomb Land
Authors: Chougule Hasham H. , Mirzamoghadam A. V.
Published: August 2018

Labyrinth seal designs for reduced leakage have been analyzed by three-dimensional CFD simulations. The objective is to learn the effect of seal geometry modifications on total leakage through the seal and arrive at an advanced seal setting for improved seal effectiveness through reduction in leakage. Numerical modeling of the flow field were conducted at various operating conditions. The baseline seal model for this study is a conventional straight-through rotating four-tooth labyrinth seal and static honeycomb land having symmetrical hexagonal cells. The tooth design configurations include stepped single & double notched straight and inclined teeth. Another objective is to learn the effect of staggered honeycomb land with respect to rotor/teeth rotation. The effect of teeth inclination & teeth rotation compared to stationary is also discussed. CFD results indicate improved seal effectiveness with staggered honeycomb cell land. The maximum improvement of ∼9% was observed with stepped and notched inclined teeth configuration when combined with staggered honeycomb land. The leakage reduction leading to improvement in seal effectiveness as compared to baseline configuration is largely due to higher flow resistance, higher turbulence and higher blockages by introducing vortex in leakage flow through step and cavities.
Effect of a Planetary Gearbox on the Dynamics of a Rotor System
Authors: Tatar Ali , Schwingshackl Christoph W.
Published: August 2018

The dynamic analysis of rotors with bladed disks has been investigated in detail over many decades and is reasonably well understood today. In contrast, the dynamic behaviour of two rotors that are coupled via a planetary gearbox is much less well understood. The planetary gearbox adds inertia, mass, stiffness, damping and gyroscopic moments to the system and can strongly affect the modal properties and the dynamic behaviour of the global rotating system. The main objective of this paper is to create a six degrees of freedom numerical model of a rotor system with a planetary gearbox and to investigate its effect on the coupled rotor system. The analysis is based on the newly developed finite element software “GEAROT” which provides axial, torsional and lateral deflections of the two shafts at different speeds via Timoshenko beam elements and also takes gyroscopic effects into account. The disks are currently considered as rigid and the bearings are modelled with isotropic stiffness elements in the translational and rotational directions. A novel planetary gearbox model has been developed, which takes the translational and rotational stiffness and the damping of the gearbox, as well as the masses and inertias of the sun gear, ring gear, planet gears and carrier into account. A rotating system with a planetary gearbox has been investigated with GEAROT. The gearbox mass and stiffness parameters are identified as having a significant effect on the modal behaviour of the rotor system, affecting its natural frequencies and mode shapes. The higher frequency modes are found to be more sensitive to the parameter changes as well as the modes which have a higher deflection at the location of the gearbox on the rotor system. Compared with a single shaft system, the presence of a gearbox introduces new global modes to the rotor system and decouples the mode shapes of the two shafts. The introduction of a planetary gearbox may also lead to an increase or a reduction of the frequency response of the rotor system based on gear parameter values.
The Validation of Flutter Prediction in a Linear Cascade of Non-Rigid Turbine Blades
Authors: Slama Vaclav , Rudas Bartolomej , Ira Jiri , Macalka Ales , Eret Petr , Tsymbalyuk Volodymyr
Published: August 2018

In low-pressure steam turbines, aerodynamic and structural design of the last stage blades is critical in determining the power plant efficiency. The development of longer last stage blades which are recently over 1 meter in length is an important task for steam turbine manufactures. The design process involves a flutter analysis of last stage blade tip sections where increased unsteady aerodynamic forces and moments might endanger the blade aerodynamic stability. However, numerical design tools must be validated using measurements in test facilities under various operating conditions. In this work, ANSYS CFX is used for flutter prediction of turbine blade tip sections oscillating in a travelling wave mode. Simulations are compared to experimental results obtained from controlled flutter tests in a wind tunnel with a linear cascade of eight turbine blade profiles made of carbon fibre. Central four blades are flexibly mounted each with two degrees of freedom (i.e. bending and torsion motions). Large deflections of thin blade profiles are accounted for the estimation of unsteady aerodynamic forces and moments. A satisfactory agreement between the simulations and experiments is achieved.
Assessment of CO2 and NOx Emissions in Intercooled Pulsed Detonation Turbofan Engines
Authors: Xisto Carlos , Petit Olivier , Grönstedt Tomas , Lundbladh Anders
Published: August 2018

In the present paper, the synergistic combination of inter-cooling with pulsed detonation combustion is analyzed concerning its contribution to NOx and CO2 emissions. CO2 is directly proportional to fuel burn and can, therefore, be reduced by improving specific fuel consumption and reducing engine weight and nacelle drag. A model predicting NOx generation per unit of fuel for pulsed detonation combustors, operating with jet-A fuel, is developed and integrated within Chalmers University’s gas turbine simulation tool GESTPAN. The model is constructed using CFD data obtained for different combustor inlet pressure, temperature and equivalence ratio levels. The NOx model supports the quantification of the trade-off between CO2 and NOx emissions in a 2050 geared turbofan architecture incorporating intercooling and pulsed detonation combustion and operating at pressures and temperatures of interest in gas turbine technology for aero-engine civil applications.
Large-Eddy and RANS Simulations of Heat Transfer in a U-Duct With a High-Aspect Ratio Trapezoidal Cross Section
Authors: Hu Kenny S.-Y. , Shih Tom I-P.
Published: August 2018

Large-eddy and RANS simulations were performed to examine the details of the heat-transfer mechanisms in a U-duct with a high-aspect ratio trapezoidal cross section at a Reynolds number of 20,000. ANSYS-Fluent was used to perform the simulations. For the large-eddy simulations (LES), the WALE subgrid-scale model was employed, and its inflow boundary condition was provided by a concurrent LES of incompressible fully-developed flow in a straight duct with the same cross section and flow conditions as the U-duct. The grid resolution required to obtain meaningful LES solutions were obtained via a grid sensitivity study of incompressible fully-developed turbulent flow in a straight duct of square cross section, where data from direct numerical simulation (DNS) and experiments are available to validate and guide the simulation. In addition, the grid used satisfies Celik’s criterion, and resolves the Kolmogorov’s −5/3 law. Results were also obtained for the U-duct by using RANS, and three widely used turbulence models were examined — realizable k-ε with the two-layer model in the near-wall region, shear-stress transport (SST) model, and stress-omega full Reynolds stress model (RSM). Results obtained from LES showed unsteady flow separation to occur immediately after the turn region, which none of the RANS models could predict. By being able to capture this unsteady flow mechanism, LES was able to predict the measured heat-transfer downstream of the U-duct. The maximum relative error in the predicted local heat-transfer coefficient was less than 10% in the LES results, but up to 80% in the RANS results.
CFD Simulations for Film Cooling Holes: Comparison Between Different Isotropic and Anisotropic Eddy Viscosity Models
Authors: Dickhoff Jens , Kusterer Karsten , Bhaskar Santhosh Kumar , Bohn Dieter
Published: August 2018

In modern gas turbines, film cooling technology is essential for the protection of hot parts. Today, shaped holes are widely used, but besides others, the NEKOMIMI-shaped cooling holes have shown that there is still potential to increase the film cooling effectiveness significantly by generation of Anti-Counter-Rotating Vortices (ACRV). Within the past decade, the technology has been improved step by step at B&B-AGEMA and Kawasaki Heavy Industries Ltd.; mainly by means of numerical simulations. The laterally averaged film cooling effectiveness is typically captured with acceptable accuracy, but the experimental measurements still show a deviation from the numerically obtained results with respect to the local film cooling effectiveness distribution behind the film cooling hole. Nevertheless, the film cooling air spread out in the lateral direction is one of the keys for enhancement of the film cooling performance. Thus, more precise simulations are consequently necessary for improvement of the hole shape configuration.

The present study involves simulations of a baseline fan shaped hole configuration (“777 hole” investigated by Schroeder and Thole [1][2]) using different turbulence models available in STAR-CCM+ with isotropic and anisotropic turbulence consideration (constitutive relations). Distinct differences with respect to flow phenomena (detachments and vortex creation) can be observed depending on the applied turbulence model. In total, the results show that anisotropic viscosity strongly influences the film cooling performance prediction by CFD for prediction of the film cooling effectiveness, but none of the models provides acceptable accuracy in this regard.
A Strategy of Reactant Mixing in Methane Direct-Fired sCO2 Combustors
Authors: Manikantachari K. R. V. , Martin Scott , Vesely Ladislav , Bobren-Diaz Jose O. , Vasu Subith , Kapat Jayanta
Published: August 2018

The sCO2 power cycle concept is identified as a potentially efficient, economical, and pollutant free power generation technique for future power generation. Recent work in the literature provides some strategies and best operating conditions for direct-fired sCO2 combustors based on zero-dimensional reactor modeling analysis, however there is a need for a detailed investigation using accurate combustion chemical kinetics and thermophysical models. Here, the sCO2 combustor is modelled by coupling perfectly stirred reactor (PSR) and plug flow reactor (PFR) models. The real gas effects are incorporated using the Soave-Redlich-Kwong (SRK) equation of state. Also, the detailed Aramco 2.0 kinetic mechanism is used for the combustion kinetic rates.

It is found that the primary zone must be diluted either with thirty or forty-five percent of the total CO2 in the cycle to have a feasible combustor design. However, the forty-five percent dilution level at 950 K and 1000 K yielded a better consumption of CO, O2 and CH4. Also, the cross-sectional area of the sCO2 combustor can be scaled-down to 10 to 20 times smaller than a traditional combustor with the same power output. Further, from this investigation, it is also recommended to have a gradually increasing secondary dilution in the dilution zone, by using progressively larger diameter holes. This design would help retain relatively high temperature in the initial portion of the dilution zone and would help consume fuel species such as, CO and CH4.

It appears that, for sCO2 combustors “lean burn” is the better strategy over stoichiometric burning to eliminate CO build up at the combustor exit. The lean burn condition at equivalence ratio (ϕ) equal to 0.9 is recommended for sCO2 combustor operation. Also, the length of the dilution zone can be scaled-down to 50% by lean burn operation of the combustor. It is also observed that the lean burn increases the net turbine power. Current work provides crucial design considerations for the development of advanced sCO2 combustors to be used with direct-fired power cycles.
Analysis of Parameters Influencing Build Accuracy of a SLM Printed Compressor Outlet Guide Vane
Authors: Otubusin Adetayo , Wood Paul , Appleby John , Adamczuk Rafael
Published: August 2018

The paper describes the manufacture of an outlet guide vane (OGV) of jet engines by the Selective Laser Melting (SLM) process, in view of current challenges for conventional machining approaches such as; high airfoil profile tolerances, limited tooling access and hard to machine materials like nickel-chromium-based super alloys. Within this paper, analysis was conducted to investigate the influence of build parameters on possible distortion during printing that affect the build accuracy. These parameters include the part orientation on the build plate, thickness change to the flanges and the positioning of the support structure of each part. The configurations are 3D printed using the SLM approach. The chosen material is IN625. The printed parts are 3D scanned and the results are compared to the original CAD design. The results confirmed the presence of distortions in printed parts and the effect of parameter changes. Furthermore, it was shown that improvements to the print parameters are necessary to achieve a satisfactory profile tolerance.