bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotating Effect on Transonic Squealer Tip Cooling Performance
Authors: Zhu D. , Lu S. , Ma H. , Zhang Q. , Teng J.
Published: August 2017

The aerothermal behavior of turbine blade tip has been studied for decades, mostly using stationary linear cascade. The blade rotation effect still remains unclear to the tip research community. This paper investigates two squealer tip cooling configurations with the effect of relative casing movement. The numerical method was validated against thermal measurement obtained in a transonic wind tunnel. Further analysis is presented for cases with relative casing motion. Dramatic changes in aerodynamics and heat transfer were observed, mostly due to the strong interactions between the over tip leakage flow and the coolant injection. The need to consider the rotating effect into future experimental validation is highlighted.
Economic-Competitiveness of Dish-mGT Solar Power Generators
Authors: Gavagnin Giacomo , Sánchez David , Rodríguez José M. , Muñoz Antonio , Martínez Gonzalo S.
Published: August 2017

This paper provides an analysis of the Optimised Microturbine Solar Power generator (OMSoP) project, funded by the European Commission, as the most recent attempt to develop a dish and mGT Concentrated Solar Power generation system that is cost competitive against photovoltaics, at least in certain business cases. A first section presents the system and business cases along with other boundary conditions (technology levels) and locations of interest. Then, for each case, the specific installed costs assuming a production rate of 1000 units/year are presented as provided by the project partners. Cost reductions as high as 1000 €/kWe are possible through advanced technical specifications (for instance higher turbine inlet temperatures) and complex layouts (cycles including intercooling and reheat), thanks to a major impact on system efficiency and, hence, dish size.

From a techno-economic perspective, the OMSoP technology confirms the potential to become cost-competitive against photovoltaic systems in terms of the cost of electricity. This is discussed in the final section dedicated to project appraisal. The analysis, based on hourly simulations in order to account for offdesign performance, reveals that dish-mGT systems can make a case for certain applications despite having higher installation costs than PV panels. It is shown that under representative boundary conditions, i.e. not in any market worldwide, dish-mGT systems produce electricity at the same levelised cost as small photovoltaic installations (∼11 c€/kWhe).
A Thermodynamic Transient Model for Performance Analysis of a Twin Shaft Industrial Gas Turbine
Authors: Cruz-Manzo Samuel , Panov Vili , Zhang Yu , Latimer Anthony , Agbonzikilo Festus
Published: August 2017

In this study, a Simulink model based on fundamental thermodynamic principles to predict the dynamic and steady state performance in a twin shaft Industrial Gas Turbine (IGT) has been developed. The components comprising the IGT have been implemented in the modelling architecture using a thermodynamic commercial toolbox (Thermolib, EUtech Scientific Engineering GmbH) and Simulink environment. Measured air pressure and air temperature discharged by compressor allowed the validation of the modelling architecture. The model assisted the development of a computational tool based on Artificial Neural Network (ANN) for compressor fault diagnostics in IGTs. It has been demonstrated that modelling plays an important role to predict and monitor gas turbine system performance at different operating and ambient conditions.
On Scaling Method to Investigate High-Speed Over-Tip-Leakage Flow at Low-Speed Condition
Authors: Jiang Hongmei , He Li , Zhang Qiang , Wang Lipo
Published: August 2017

Modern High Pressure Turbine (HPT) blades operate at high speed conditions. The Over-Tip-Leakage (OTL) flow, which plays a major role in the overall loss generation for HPT, can be high-subsonic or even transonic. In practice from the consideration of problem simplification and cost reduction, the OTL flow has been studied extensively in low speed experiments. It has been assumed a redesigned low speed blade profile with a matched blade loading should be sufficient to scale the high speed OTL flow down to the low speed condition.

In this paper, the validity of this conventional scaling approach is computationally examined. The CFD methodology was firstly validated by experimental data conducted in both high and low speed conditions. Detailed analyses on the OTL flows at high and low speed conditions indicate that, only matching the loading distribution with a redesigned blade cannot ensure the match of the aerodynamic performance at the low speed condition with that at the high-speed condition. Specifically, the discrepancy in the peak tip leakage mass flux can be as high as 22.2%, and the total pressure loss at the low speed condition is 10.7% higher than the high speed case.

An improved scaling method is proposed hereof. As an additional dimension variable, the tip clearance can also be “scaled” down from the high speed to low speed case to match the cross-tip pressure gradient between pressure and suction surfaces. The similarity in terms of the overall aerodynamic loss and local leakage flow distribution can be improved by adjusting the tip clearance, either uniformly or locally. The limitations of this proposed method are also addressed in this paper.
Improvement of Impaired Combustion Conditions at Some Off-Design Operation by Driving a Precisely Controlled Modulation of the Burner Air Feed
Authors: Giuliani Fabrice , Pfefferkorn Lukas , Kraft Gerhard
Published: August 2017

A non-conventional method based on forced-flow combustion oscillations is investigated regarding the improvement of combustion conditions at suboptimal operating conditions.

In the field of gas turbines, uncontrolled combustion oscillations are called combustion instabilities and they have been extensively studied over the last two decades. Low NOx systems that operate in the lean combustion domain are prone to enable combustion instabilities. A common way to investigate combustion instabilities is to reproduce these with help of an acoustic driver, e.g. using a loudspeaker or a fast valve in order to drive forced-flow combustion oscillations. When the oscillations match with one of the natural resonant frequencies of the combustor cavities or of the feeding pipes, the thermoacoustic coupling can occur in a well-controlled way.

Some positive effects of this type of forcing can be found in the literature. In a similar context, it was shown in a previous work (GT2015-42377) under which conditions and by how far a forced-flow thermoacoustic drive can further push the lean-blow-out limits in the lean region. Following to this work, it is described that driving a resonant flame can also be beneficial regarding combustion quality. Better combustion performances were observed with the help of pulsating the burner air feed at part-load conditions on a premixed swirling flame, where combustion quality is known to be impaired at steady-state.

The presented technology can then be seen as a flexible On-Off thermoacoustic drive, based on forced pulse combustion and using a siren tunable in frequency and amplitude in a refined way. The benefits and the challenges about its hypothetic implementation in the field of turbomachinery conclude this paper.
Experimental Investigation of the Influence of the Shear Layer on Direct Combustion Noise of a Turbulent Jet Flame
Authors: Nawroth Holger , Paschereit Christian Oliver
Published: August 2017

This work presents results from experiments on direct combustion noise emitted from an unconfined, turbulent, premixed jet flame. It focuses on the influence of the shear layer and the turbulent fluctuations within this layer on the resulting noise emissions. Orifice discs of different diameter are used to change the shear layer width of the emanating jet. Using these discs, which induce and increase blockage upstream of the reaction zone, leads to significantly higher turbulent fluctuations of the velocity and subsequently to wider shear layers. As these fluctuations in the shear layer are the origin of direct combustion noise, the sound pressure levels of reacting flows increase as well. Moreover, the experiments also show the impact of the Reynolds number and equivalence ratio on noise emissions when using these discs. In general, wider shear layers yield higher sound pressure levels of the resulting combustion noise. Although amplitudes of the resulting noise emissions might differ for different conditions, the normalized sound spectra coincide proving that turbulent velocity fluctuations only govern the sound pressure levels but do not affect the shape of the resulting spectra if the geometry and fuel remain the same.
Numerical Studies on Combustor-Turbine Interaction at the Large Scale Turbine Rig (LSTR)
Authors: Hilgert Jonathan , Bruschewski Martin , Werschnik Holger , Schiffer Heinz-Peter
Published: August 2017

In order to fully understand the physical behavior of lean burn combustors and its influence on high pressure turbine stages in modern jet engines, the use of Computational Fluid Dynamics (CFD) promises to be a valuable addition to experimental techniques. The numerical investigations of this paper are based on the Large Scale Turbine Rig (LSTR) at Technische Universität Darmstadt, Germany which has been set up to explore the aerothermal combustor turbine interaction. The underlying numerical grids of the simulations take account of the complex cooling design to the fullest extent, considering coolant cavities, cooling holes and vane trailing edge slots within the meshing process. In addition to the k-ω-SST turbulence model, Scale-Adaptive Simulation (SAS) is applied for a computational domain comprising swirl generator and nozzle guide vanes in order to overcome the shortcomings of eddy viscosity turbulence models with regard to streamline curvature. The numerical results are compared with Five Hole Probe measurements at different streamwise locations showing good agreement and allowing for a more detailed examination of the complex flow physics caused by the interaction of turbine flow with lean-burn combustion and advanced film-cooling concepts. Moreover, numerically predicted Nu-contours on the hub end wall of the nozzle guide vane are validated by means of Infrared Thermography measurements.
Experimental and LES Analysis of a Premix Swirl Burner Under Acoustic Excitation
Authors: Biagioli F. , Wysocki S. , Alemela R. , Srinivasan S. , Denisov A.
Published: August 2017

The frequency response to acoustic excitation of turbulent premixed flames stabilized in a high swirl flow is investigated with high speed diagnostics and Large Eddy Simulation (LES). In both cases, the flame transfer function (FTF), i.e. the frequency response of the total heat release, is also determined. Both experiments and LES show distributions of the FTF amplitude and phase which are different from flames stabilized in non swirling flows, for example piloted conical premixed flames. In order to shed light on these differences, the effect on the FTF of the swirl velocity fluctuation driven by a forced harmonic perturbation in the reactant flow rate is isolated in the LES simulations using a novel methodology that makes use of the Proper Orthogonal Decomposition (POD). The typical FTF distributions observed in experiments for swirl stabilized flames are interpreted on the basis of this separation. A close link with the frequency response of the velocity field distribution in the combustor is also established.
Experimental and Numerical Investigation of the Performance Impact of a Heavily Off-Design Inlet Swirl Angle in a Steam Turbine Stage
Authors: Paradiso Berardo , Gatti Giacomo , Mora Alessandro , Dossena Vincenzo , Arcangeli Lorenzo , Maceli Nicola , Bellucci Juri
Published: August 2017

The aim of this work is to provide an insight into the performance reduction of a 1.5 axial steam turbine stage working under extreme incidence conditions at the inlet. In particular, the main object of the study is the propagation of the loss cores across the blade rows, so as to assess how such operating conditions affect the full machine. Experimental data have been used to validate an unsteady three-dimensional numerical simulation, which provided the tools to investigate the flowfield in detail. To do so, the 1.5 turbine stage installed in the Low Speed Test Rig at Politecnico di Milano has been tested with design and off-design inlet conditions by modifying the IGV orientation. The inter-stage flowfield was investigated by traversing pressure probes in three different axial planes, downstream of each blade row. The numerical simulation has been carried out at University of Florence. The experimental data from probes traversing was used as boundary conditions so as to match as closely as possible the actual operative parameters of the stage. Data from flange-to-flange measurements on the test rig were also used to compare the stage efficiency. After the successful validation of the numerical results, the loss cores propagation study itself was carried out. Using CFD results, the unsteady nature of the separation occurring on the first stator in off-design condition is investigated. Subsequently, a detailed analysis of the propagation of the loss cores is presented, including loss coefficients calculation and entropy trends along the machines axial coordinate. The main outcome is that at the machine exit the loss structures appear to be mainly mixed out and, therefore, subsequent stages would operate under conditions not far from the nominal ones.
Characterization of Non-Equilibrium Condensation of Supercritical Carbon Dioxide in a de Laval Nozzle
Authors: Lettieri Claudio , Paxson Derek , Spakovszky Zoltan , Bryanston-Cross Peter
Published: August 2017

On a ten-year timescale, Carbon Capture and Storage could significantly reduce carbon dioxide (CO2) emissions. One of the major limitations of this technology is the energy penalty for the compression of CO2 to supercritical conditions, which can require up to 15% of the plant’s gross power output. To reduce the power requirements supercritical carbon dioxide compressors must operate at reduced temperatures and near saturation where phase change effects are important. Non-equilibrium condensation can occur in the high-speed flow at the leading edge of the compressor, causing performance and stability issues. The characterization of the fluid at these conditions is vital to enable advanced compressor designs at enhanced efficiency levels but the analysis is challenging due to the lack of data on the metastable fluid properties.

In this paper we assess the metastable behavior and nucleation characteristics of high-pressure subcooled carbon dioxide during the expansion in a Laval nozzle. The assessment is conducted with numerical calculations, supported and corroborated by experimental measurements. The Wilson line is determined via optical measurements in the range of 41 and 82 bar and near the critical point. The state of the metastable fluid is fully characterized through pressure and density measurements, with the latter obtained in a first of its kind laser interferometry set up. In a systematic analysis the inlet conditions of the nozzle are moved close to the critical point to allow for large gradients in fluid properties and reduced margin to condensation. The results of calculations using a direct extrapolation of the Span and Wagner equation of state model are compared with the experimental measurements. The analysis suggests that the direct extrapolation using the Span and Wagner model yields results within 2% of the experimental data, with improved accuracy at conditions away from the critical point. The results are applied in a pre-production supercritical carbon dioxide compressor and are used to define inlet conditions at reduced temperature but free of condensation. Full-scale compressor experiments demonstrate that the new inlet conditions can reduce the shaft power input by 16%.
Advanced Statistical Analysis Estimating the Heat Load Issued by Hot Streaks and Turbulence on a High-Pressure Vane in the Context of Adiabatic Large Eddy Simulations
Authors: Thomas Martin , Duchaine Florent , Gicquel Laurent , Koupper Charlie
Published: August 2017

The next generation of lean combustion engines promises to further decrease environmental impact and cost of air traffic. Compared to the currently employed Rich Quench Lean (RQL) concept, the flow field at the exit of a lean combustion chamber is characterized by stronger variations of velocity as well as temperature and higher levels of turbulence. These specific features may have a substantial impact on the aerothermal performance of the high-pressure turbine and thereby on the efficiency of the entire engine. Indeed, high levels of turbulence in the Nozzle Guide Vane (NGV) passages locally impact the heat flux and result in globally over dimensioned cooling systems of the NGV. In this study, Large Eddy Simulations (LES) are performed on an engine representative lean combustion simulator geometry to investigate the evolution of turbulence and the migration of hot streaks through the high-pressure turbine. To investigate the impact of non-uniform stator inlet conditions on the estimated thermal stress on the NGVs, adiabatic LES predictions of the lean combustor NGV FACTOR configuration are analyzed through the use of high statistical moments of temperature and two point statistics for the assessment of turbulent quantities. Relations between temperature statistical features and turbulence are evidenced on planes through the NGV passage pointing to the role of mixing and large scale features along with marked wall temperatures that locally can largely differ from obtained mean values.
Development and Evaluation of a Mobile Plant to Prepare Natural Gas for Use in Foam Fracturing Treatments
Authors: Beck Griffin , Poerner Melissa , Hoopes Kevin , Verma Sandeep , Sridhar Garud , Phatak Alhad
Published: August 2017

Hydraulic fracturing treatments are used to produce oil and gas reserves that would otherwise not be accessible using traditional production techniques. Fracturing treatments require a significant amount of water, which has an associated environmental impact. In recent work funded by the Department of Energy (DOE), an alternative fracturing process has been investigated that uses natural gas as the primary fracturing fluid. In the investigated method, a high-pressure foam of natural gas and water is used for fracturing, a method than could reduce water usage by as much as 80% (by volume). A significant portion of the work focused on identifying and optimizing a mobile processing facility that can be used to pressurize natural gas sourced from adjacent wells or nearby gas processing plants.

This paper discusses some of the evaluated processes capable of producing a high-pressure (10,000 psia) flow of natural gas from a low-pressure source (500 psia). The processes include five refrigeration cycles producing liquefied natural gas as well as a cycle that directly compresses the gas. The identified processes are compared based on their specific energy as calculated from a thermodynamic analysis. Additionally, the processes are compared based on the estimated equipment footprint and the process safety. Details of the thermodynamic analyses used to compare the cycles are provided. This paper also discusses the current state of the art of foam fracturing methods and reviews the advantages of these techniques.
A Coupled 1D Film Hydrodynamics and Core Gas Flow Model for Air-Oil Flows in Aero-Engine Bearing Chambers
Authors: Kakimpa B. , Morvan H. P. , Hibberd S.
Published: August 2017

A robust 1D film hydrodynamic model has been sequentially coupled with a 1D core gas model and used to predict the instantaneous mean core gas speed, film interface shear stress and liquid film distribution within an idealised bearing chamber. This novel approach to aero-engine bearing chamber simulation provides a predictive tool that can be used for the fast and reliable exploration of a set of bearing chamber design and operating conditions characterised by the: chamber dimensions, air/oil fluid properties, shaft speed, sealing air flows, oil feed rates and sump scavenge ratios. A preliminary validation of the model against available bearing chamber flow measurements from literature shows good agreement. The model represents a significant step change in predictive capabilities for aero-engine oil system flows compared to previous semi-empirical models. The bearing chamber is idealised as a one-dimensional (2D) domain with a predominantly azimuthal flow in both the rotational oil film and core gas such that axial components may be ignored. A 1D system of depth-averaged film hydrodynamics equations is used to predict oil film thickness and mean speed distributions in the azimuthal direction under the influence of interface shear, gravity, pressure gradient and surface tension forces. The driving shear stress in the film model is obtained from the 1D core-gas model based on an azimuthal gas momentum conservation equation which is coupled to the film model through the interface shear stress and film interface velocity.
Effect of Combustion on Turbulence in a Gas Turbine Combustion Chamber
Authors: Adoua Richard , Page Gary J.
Published: August 2017

Large Eddy Simulations of a lab scale single sector of a lean burn aero-engine combustor have been undertaken for both isothermal and reacting flows in order to examine the effect of combustion on the flow features and velocity fluctuations. For that purpose, use was made of the Rolls-Royce pressure based solver, PRECISE-UNS, to perform simulations. Unresolved subgrid stresses were modelled by the Wall-Adapting Local Eddy-viscosity (WALE) model and combustion by the FGM model. The liquid-phase of fuel spray uses an Eulerian-Lagrangian approach, where the trajectories of a number of fuel droplets are calculated by stepping in time. Comparison is made with experimental PIV data at the exit of the combustor for mean velocities and velocity fluctuations. The analysis of the flow inside the combustor chamber showed the classical features of turbulent confined highly swirling flow under isothermal and as well as under reacting conditions. In fact, a large central recirculation zone on the x-axis and two corner recirculation zones were found. The effect of combustion in this study is to reduce the opening angle of the jet and as a result the size of the central recirculation zone is reduced while the ones at the corner of the combustor increases. Under isothermal conditions the occurrence of the precessing vortex core (PVC) was found at the frequency of ∼82Hz with high amplitude. This produces regions with high velocity fluctuations. Under reacting conditions the PVC is damped and its frequency is shifted to ∼95 Hz and its amplitude is considerably reduced. In term of velocity fluctuations, in general, results illustrated that, under combustion configuration they are considerably reduced resulting in low turbulence intensity.
Three-Dimensional Aerodynamic Analysis of a Darrieus Wind Turbine Blade Using Computational Fluid Dynamics and Lifting Line Theory
Authors: Balduzzi Francesco , Bianchini Alessandro , Ferrara Giovanni , Marten David , Pechlivanoglou George , Nayeri Christian Navid , Paschereit Christian Oliver , Drofelnik Jernej , Campobasso Michele Sergio , Ferrari Lorenzo
Published: August 2017

Due to the rapid progress in high-performance computing and the availability of increasingly large computational resources, Navier-Stokes computational fluid dynamics (CFD) now offers a cost-effective, versatile and accurate means to improve the understanding of the unsteady aerodynamics of Darrieus wind turbines and deliver more efficient designs.

In particular, the possibility of determining a fully resolved flow field past the blades by means of CFD offers the opportunity to both further understand the physics underlying the turbine fluid dynamics and to use this knowledge to validate lower-order models, which can have a wider diffusion in the wind energy sector, particularly for industrial use, in the light of their lower computational burden.

In this context, highly spatially and temporally refined time-dependent three-dimensional Navier-Stokes simulations were carried out using more than 16,000 processor cores per simulation on an IBM BG/Q cluster in order to investigate thoroughly the three-dimensional unsteady aerodynamics of a single blade in Darrieus-like motion. Particular attention was payed to tip losses, dynamic stall, and blade/wake interaction. CFD results are compared with those obtained with an open-source code based on the Lifting Line Free Vortex Wake Model (LLFVW). At present, this approach is the most refined method among the “lower-fidelity” models and, as the wake is explicitly resolved in contrast to BEM-based methods, LLFVW analyses provide three-dimensional flow solutions. Extended comparisons between the two approaches are presented and a critical analysis is carried out to identify the benefits and drawbacks of the two approaches.
Experimental Investigation on Power Losses due to Oil Jet Lubrication in High Speed Gearing Systems
Authors: Massini D. , Fondelli T. , Facchini B. , Tarchi L. , Leonardi F.
Published: August 2017

In order to reduce environmental and climate impact from air traffic, the main effort of aero-engine industry and research community is looking at a continuous increase in gearbox efficiency. With this kind of components every source of loss can be responsible for high heat loads; for this reason oil jet systems are used to provide proper cooling and lubrication of gears tooth surfaces. In the design phase it is important to predict the losses increase due to the lubricating oil jet impact on the spur gear, varying the different geometrical and working parameters such as the jet inclination, distance and the oil mass flow rate and temperature. An experimental investigation was carried out on a novel rotating test rig able to reproduce real engine working conditions in terms of speed, pressure and lubrication system, for a single spur gear. The rig consists of an electric spindle driving a shaft with a spur gear clamped on top. The gear is enclosed in a box where different air pressure conditions can be set and monitored. Pressure transducers and T-type thermocouples placed within the test box were used to measure the gear working conditions. The test box is also equipped with several optical accesses allowing flow field measurements or oil jet visualizations. The driving shaft is composed by two parts connected by a bearingless torquemeter equipped with a speedometer in order to perform torque losses and rotating velocity measurements. Tests were performed without the gear first, in order to separate the final value from the friction losses due to the driving shaft. Windage losses were characterized experimentally for every working condition and the results collected in a simple correlation that was used to separate the losses due to air windage from the ones due to the oil injection. An oil control unit allowed to impose the proper oil pressure and temperature conditions and to measure the mass flow rate. The oil jet was delivered by a spraybar placed within the gearbox, the jet to gear distance and relative angle were varied during the experiments. High speed visualizations were also performed for every test condition in order to deepen the physical understanding of the phenomena and to obtain more information on the lubrication capability of every jet condition. A high speed camera was placed in front of the gear exploiting an optical access while a halogen lamp was used to provide the proper lightening necessary due to the very low exposure time of the acquisitions. The wide experimental database provided, allowed the development of a simple numerical model able to well predict every losses contribution at the various working conditions.
An Integrated Conjugate Computational Approach for Evaluating the Aerothermal and Thermomechanical Performance of Double-Wall Effusion Cooled Systems
Authors: Murray Alexander V. , Ireland Peter T. , Rawlinson Anton J.
Published: August 2017

The drive to further increase gas turbine thermal efficiency and specific power output continue to elevate core temperatures well beyond the natural capabilities of the metals employed in their manufacture necessitating increasingly complex cooling systems.

One such cooling mechanism is the double-wall, effusion-cooled system which combines in a very compact format, many cooling aspects already implemented in gas turbine cooling. To-date, thermomechanical stresses have provided one of the more significant challenges in the implementation of these systems and needs to be considered — alongside aerothermal performance — at the initial stages of design.

This paper presents a novel computational method that has been developed to allow an integrated assessment of both the aerothermal and thermomechanical performance of double-wall cooling geometries. A decoupled conjugate method was developed in which internal cooling performance was ascertained via a conjugate CFD model in which the mainstream flow was not simulated. Instead, external film cooling performance was assessed via a superposition method that was developed and applied to a two-dimensionally varying correlation allowing streamwise film development to be modelled. Results of both the internal and external cooling simulations were then utilised in a conduction model to develop a complete thermal assessment of the geometry. The calculated temperature distribution was used in a thermomechanical FEA analysis permitting an insight into the stress field developed within the double-wall geometry under thermal load.

The developed method was demonstrated in the assessment of seven circular pedestal, double-wall geometries in which a range of geometric parameters were investigated. The results provide an insight into the effect of varying these parameters on both the aerothermal performance of the selected geometries, along with the effect on the thermomechanical stress field developed.
Detailed Analysis of the Wake Structure of a Straight-Blade H-Darrieus Wind Turbine by Means of Wind Tunnel Experiments and CFD Simulations
Authors: Bianchini Alessandro , Balduzzi Francesco , Ferrara Giovanni , Ferrari Lorenzo , Persico Giacomo , Dossena Vincenzo , Battisti Lorenzo
Published: August 2017

Darrieus Vertical Axis Wind Turbines (VAWTs) have been recently identified as the most promising solution for new types of applications, such as small-scale installations in complex terrains or offshore large floating platforms. To improve their efficiencies further and make them competitive with those of conventional horizontal axis wind turbines, a more in depth understanding of the physical phenomena that govern the aerodynamics past a rotating Darrieus turbine is needed. Within this context, Computational Fluid Dynamics (CFD) can play a fundamental role, since it represents the only model able to provide a detailed and comprehensive representation of the flow. Due to the complexity of similar simulations, however, the possibility of having reliable and detailed experimental data to be used as validation test cases is pivotal to tune the numerical tools.

In this study, a two-dimensional U-RANS computational model was applied to analyze the wake characteristics on the mid plane of a small-size H-shaped Darrieus VAWT. The turbine was tested in a large-scale, open-jet wind tunnel, including both performance and wake measurements. Thanks to the availability of such a unique set of experimental data, systematic comparisons between simulations and experiments were carried out analyzing the structure of the wake, and correlating the main macro-structures of the flow to the local aerodynamic features of the airfoils in cycloidal motion. In general, good agreement on the turbine performance estimation was constantly appreciated.
Design and Operational Development a Pneumatic Braking System for a Gas-Turbine Units Test Bench
Authors: Matveev Valeriy , Novikova Yulia , Popov Grigorii , Baturin Oleg , Goriachkin Evgenii
Published: August 2017

Each gas turbine engine must be tested after it has been produced or repaired. If the engine is used to generate power on the output shaft, its power must be utilized during the test process. To do this, pneumatic brake system can be applied. It allows to measure and utilize the power generated by the engine by using this power to drive a single compressor connected through the clutch with the output shaft of the engine under test. The process of gas-dynamic designing of the pneumatic braking system for a modernized gas-turbine engine NK-36ST is described in detail in this paper. Computational model was created by using Numeca Fine / Turbo and was verified using the experimental data of the baseline compressor. Also, research efforts which are aimed at improving the efficiency of the pneumatic braking system and increasing its gasdynamic stability were conducted. In particular, guide vane was added and the contours of its flow channel were modified. Also the exhaust nozzle was designed for the pneumatic braking system to ensure its work at the required operating points.
Gas Turbine Machinery Diagnostics: A Brief Review and a Sample Application
Authors: Allen Cody W. , Holcomb Chad M. , de Oliveira Mauricio
Published: August 2017

The intersection of machine learning methods and gas turbine sensor data has expanded rapidly in the last decade to include numerous applications of regression, clustering, and even neural network algorithms. Learning algorithms have pushed traditional engine health management into the realm of prognostic health management. This paper starts with a review of several common computational methods used to monitor the condition of gas turbines currently employed by both industry and academia. Sources of application of machine learning algorithms from outside the gas turbine industry are also brought in. Focus is generally placed on industrial gas turbines with an industry standard monitoring system. The authors explore beyond gas path analysis with a novel use of machine learning algorithms to engine component classification. The paper concludes with a case study of applying learning algorithms to machine data to identify different fuel valves.
Cooling System Optimization of Combustor Liners
Authors: Pucci Egidio , Cerutti Matteo , Peano Guido , Facchini Bruno , Andreini Antonio
Published: August 2017

The optimization process of liner cooling system of industrial annular combustor is performed, since the early phase of design, by means of an innovative in house code, performing a one-dimensional conjugate aero-thermal-strain analysis.

The liner cold side heat transfer coefficients in a turbulated forced convection region are iteratively computed updating metal and air temperatures and the deformed geometry of coolant passages from results of a heat balance. Coolant passages, in between the deformed surfaces of liner and baffle, influence the local velocity, changing heat transfer coefficients and coolant pressure losses. The liner and baffle strain computation has been validated comparing the code results with the ones obtained by a detailed finite element model.

The correlations embedded in the code are calibrated thanks to a thermal and pressure data matching performed with experimental measurements acquired in a full annular rig test campaign.

The optimization process, maintaining the same coolant pressure losses, minimizes the axial metal temperature gradients distribution, reducing the thermal induced stresses: the resulting liners durability can be significantly enhanced, without penalizing engine performance.
Fuel Flexibility of a Multi-Staged Prototype Gas Turbine Burner
Authors: Kundu Atanu , Klingmann Jens , Subash Arman Ahamed , Collin Robert
Published: August 2017

Gas turbines are widely used power generation equipment and very important for its efficiency and flexible operability. With the increasing demand of low carbon or less greenhouse gas emission from gas turbine, usage of clean fuel (i.e. hydrogen) is highly recommended. Adaptation with various type of fuels without any operability issues are the primary focus of interest while design and development of a low NOx gas turbine combustion system. Due to chemical and physical property variation of different fuel, a common combustion system design is complex and require extensive testing. The present paper is focused on fuel flexibility of an industrial prototype burner, designed and manufactured by Siemens Industrial Turbomachinery AB, Sweden. In this work, a baseline case (Methane fuel) is compared with different custom fuel blends (mixture of methane with natural gas and hydrogen). The primary and secondary combustion characteristics were modified when hydrogen blended fuels were introduced. The Lean Blowout limit was extended for the primary and secondary flames. The secondary flame macro structure was captured using Planar Laser Induced Fluorescence and natural luminosity imaging; whereas primary flame location was characterized by the thermocouple readings. Operational stability map and emission (NOx and CO) capability of the burner was determined from the experiment. Numerical calculation using ANSYS FLUENT was performed to simulate the combustion process and compare the results with experiment. The experimental and simulation effort provided information about the flame macrostructure and operability (lean operability limit was extended by 100 K) of the new technology burner when the combustion system was exposed to different type of fuels.
Conceptual Design of an Axial Turbocharger Turbine
Authors: Pesiridis Apostolos , Ferrara Antonio , Tuccillo Raffaele , Chen Hua
Published: August 2017

Despite engine turbocharging being a widespread technology, there are still drawbacks present in current turbocharging systems stemming from the apparent mismatch between the periodic operation of a piston engine operating in conjunction with an essentially steady-state, rotordynamic machine (turbocharger). The primary issue remains the provision of adequate transient response thereby suppressing the issue of turbocharger lag (turbo-lag) or the poor initial response of the turbocharger to driver-commanded, engine operating point changes due to its inertia. Another problem is engine-turbocharger matching and operation under pulsating conditions in the exhaust manifold and generally unsteady engine operating conditions. The exhaust flows of internal combustion engines are characterized by pulsating flows at constant engine speeds (local pulsating effect) as well as “global” unsteadiness during engine transient events. Because of the volute volume and the length of the flow path, this unsteadiness generates a phase shift between mass flow, temperature and pressure at rotor inlet, and a stronger circumferential variation of the rotor inlet condition than in steady flow conditions. The shift and the variation increase the losses in the turbine, resulting in lower turbine efficiency.

The current paper develops original concept work carried out at Brunel University London to develop an innovative fluid-dynamic design for an axial turbine for turbocharger application. An axial flow turbine coupled with a specially-designed, outflow volute, arranged in a non-classical way, are the target of this work. CFD analysis and 1D simulation of an engine coupled with the innovative turbine have been performed to highlight the design potential.
Uncertainty Quantification in Large Eddy Simulations of a Rich-Dome Aviation Gas Turbine
Authors: Masquelet Matthieu , Yan Jin , Dord Anne , Laskowski Gregory , Shunn Lee , Jofre Lluis , Iaccarino Gianluca
Published: August 2017

In this work, a rich-dome aviation combustor operating over a range of high-power conditions is investigated using multiple Large Eddy Simulations (LES). The LES flow solutions are obtained with CharLES, a massively-parallel framework for compressible, reacting flows in complex geometries. The CharLES solver constructs a body-conforming mesh from the 3D Voronoi diagram of a set of regularly distributed seed points within the computational domain. The computational domain spans from the compressor exit plane to the combustor exit plane and includes the passages around the combustor liners. A baseline solution is first obtained at nominal conditions using a reference grid and validated using non-dimensional exit profile. Non-intrusive Uncertainty Quantification (UQ) is then employed to characterize the uncertainties on a few key combustor metrics. It is found that the overall variability at the exit plane is actually larger than the input uncertainty. This highlights the non-linear coupling between the flow and the reacting processes inside the combustor. Areas of high temperature variability are highlighted, especially downstream of the dilution holes. Finally, it is found that uncertainty in fuel flowrate has a greater impact on outlet quantities whereas uncertainty in air inlet temperature has a greater impact on liner quantities.
Model Reference Adaptive Control of a Turbofan Engine Using Output-Feedback
Authors: Cline C. Harvey O. , Silverstein Donald M. , Skertic Richard J. , Żak Stanisław H.
Published: August 2017

A novel, output-feedback, model reference adaptive controller (MRAC) architecture is proposed for a class of multi-input multi-output (MIMO) dynamical systems. The proposed controller is developed using a design model that contains artificial input, which may model uncertainties or nonlinearities of the controlled system. First, the ideal controller is constructed that contains the artificial input modeling the controlled system uncertainties or nonlinearities. The proposed controller is obtained by replacing the artificial input in the ideal controller with its estimate obtained using an adaptive dynamical component. It is then shown that the system unknown uncertainties or nonlinearities are asymptotically reconstructed. Linear matrix inequalities (LMIs) are used to compute the proposed controller parameters. The controller was implemented and tested on NASA’s Commercial Modular Aero-Propulsion System Simulation 40k (C-MAPSS40k) model of a typical twin spool, high-bypass turbofan engine in the 40,000-pound takeoff thrust class. The performance of the proposed controller compares favorably against the built-in controller of C-MAPSS40k. This paper presents a derivation and initial proof of concept. It is appropriate to conduct proof-of-concept work at a single design point (small signal design and analysis) before expanding the envelope. Thus, we performed the small signal design analysis and simulation and the results of our analysis are presented in this paper.
Toward Affordable Uncertainty Quantification for Industrial Problems: Part I — Theory and Validation
Authors: Ghisu Tiziano , Shahpar Shahrokh
Published: August 2017

Non-intrusive Polynomial Chaos (NIPC) methods have become popular for uncertainty quantification, as they have the potential to achieve a significant reduction in computational cost (number of evaluations) with respect to traditional techniques such as the Monte Carlo approach, while allowing the model to be still treated as a black box.

This work makes use of Least Squares Approximations (LSA) in the context of appropriately selected PC bases. An efficient technique based on QR column pivoting has been employed to reduce the number of evaluations required to construct the approximation, demonstrating the superiority of the method with respect to sparse grid quadratures and to LSA with randomly selected quadrature points. Orthogonal (or orthonormal) polynomials used for the PC expansion are calculated numerically based on the given uncertainty distribution, making the approach optimal for any type of input uncertainty.

The benefits of the proposed techniques are verified on a number of analytical test functions of increasing complexity and on two engineering test problem (uncertainty quantification of the deflection of a 3- and a 10-bar structure with up to 15 uncertain parameters). The results demonstrate how an LSA approach within a PC framework can be an effective method for UQ, with a significant reduction in computational cost with respect to full tensor and sparse grid quadratures.
Flow Resistance Coefficients of Porous Brush Seal As a Function of Pressure Load
Authors: Doğu Yahya , Sertçakan Mustafa C. , Gezer Koray , Kocagül Mustafa
Published: August 2017

Developments in brush seal analyses tools have been covering advanced flow and structural analyses since brush seals are applied at elevated pressure loads, temperatures, surface speeds, and transients. Brush seals have dynamic flow and structural behaviors that need to be investigated in detail in order to estimate final leakage output and service life. Bristles move, bend and form a grift matrix depending on pressure load. The level of pressure load determines the tightness of the bristle pack, and thus, the leakage. In the CFD analyses of this work, the bristle pack is treated as a porous medium. Based on brush seal test data, the flow resistance coefficients (FRC) for the porous bristle pack are calibrated as a function of pressure load. A circular seal is tested in a static test rig under various pressure loads at room temperature. The FRC calibration is based on test leakage and literature based axial pressure distribution on the rotor surface and radial pressure distribution over the backing plate. The anisotropic FRC are treated as spatial dependent in axi-symmetrical coordinates. The fence height region and the upper region of bristle pack have different FRC since the upper region is supported by backing plate while bristles are free to move and bend at the fence height region. The FRC are found to be almost linearly dependent on the pressure load for investigated conditions. The blow-down is also calculated by incorporating test leakage and calibrated FRC.
Design for Additive Manufacturing: Valves Without Moving Parts
Authors: Gaymann A. , Montomoli F. , Pietropaoli M.
Published: August 2017

This work presents an innovative design method to obtain valves without moving parts that can be built using additive manufacturing and applied to gas turbines. Additive manufacturing offers more flexibility than traditional manufacturing methods, which implies less constraints on the manufacture of engineering parts and it is possible to build complex geometries like the Tesla valve. The Tesla valve is a duct that shows a diodicity behavior: it allows a fluid to flow in one direction with lower losses than in the other one. Unfortunately the design of the Tesla valve is two dimensional and it relies on the designer experience to obtain good performance.

The method presented here allows the automatic generation of valves similar to the Tesla one, obtained automatically by a topology optimization algorithm. It is the first time that a three dimensional method is presented, the available algorithms in the open literature works in two dimensions. A fluid sedimentation process enables the creation of a new geometry optimized to meet a prescribed set of performance, such as pressure losses. The steepest descent method is used to approximate the integrals met during the calculation process.

The optimizer is used to obtain three dimensional geometries for different multi-objective functions. The geometry is compared to an existing similar solution proposed in the open literature and validated. The results are compared to a Tesla valve to show the performance of the optimized geometries. The advantage of the proposed solution is the possibility to apply the design method with any spatial constraints and for a wide range of mass flow.