bluuebunny/crossref_metadata_2025 huggingface dataset:
Field Qualification of an Improved DLE Gas Turbine Control Algorithm to Reduce Part Load Emissions
Authors: Cowell Luke , Roesch James , Camou Alejandro , Caron Tim , Ritchie Jason , Carlos Ivan
Published: November 2019

The importance of expanded operating flexibility with reduced emissions on dry low emissions (DLE) gas turbines to lower loads has grown in importance for operators in many applications including natural gas transmission. Solar Turbines has developed an improved emissions control algorithm for Solar’s SoloNOx DLE gas turbines being offered as Enhanced Emissions Control. The new algorithm reduces carbon monoxide (CO) and unburned hydrocarbons (UHC) emissions from idle to 50% load. The corresponding startup and shut down emissions are reduced so that operators can obtain permits for operation over longer periods outside of low emissions mode. The algorithm has been evaluated in field trials at two different compressor stations using different gas turbine engine models. Solar’s Taurus™ 60 was tested at a field site in West Virginia and a Mars® 100 was tested near Houston, Texas in the United States. The new control scheme reduces emissions from part load down to idle. The new controls extend the bleed valve or variable guide vanes’ operating range where they modulate to control combustor temperature from idle to full load. The pilot fuel schedule is also changed to work more directly with the combustor temperature control.

Two field trials were completed to measure emissions continuously for more than 10 months at each site to validate the effectiveness of the new algorithm. Operation of the test units was largely at loads over 50% and the continuous data served to validate that the new algorithm with the modifications to pilot control did not change the emissions signature in the ‘low emissions mode.” In addition, multiple site visits were completed to map emissions from idle to 50% load over a range of engine settings. This mapping fully documented the complete emissions performance of the test units from idle to 100% load over a range of ambient temperatures from below freezing to 38°C.

The field trials validate that the improved controls reduce CO and UHC emissions from idle to 50% load when compared to the current production algorithm. The testing also validated that the emissions above 50% load were unchanged compared to the current control algorithm. Specifically, CO and UHC emissions were reduced by 35 to 99% over the idle to 50% load operating range. By optimizing the pilot fuel controls the NOx emissions were also reduced 20 to 75% from idle to 50% load. The algorithm makes it possible to offer 15 ppm NOx warranties for the subject engine models in gas transmission applications down to 40% load that have been restricted to 50% load and higher. Over the wide ambient temperature range experienced during the field trial periods, emissions were consistent and no clear trends were documented with ambient temperature or engine speed (load).
Numerical Study on the Flow and Heat Transfer Characteristics With Different Rib Structures Placed on the Impingement Plate
Authors: Ding Yong-feng , Zhu Hui-ren , Gao Qiang
Published: November 2019

Jet impingement cooling is an important way to cool turbine blades. Ribbed channels are widely used in the chord region of turbine blades and are an important internal cooling structure. In the design process of the internal cooling structure of the conventional turbine blade, it is the primary consideration of the designer to improve the heat transfer coefficient at the surface of the inner cooling passage. With the development of the design of the inner cooling structure of the turbine blade, the pressure loss caused by the inner cooling passage has been paid more and more attention. Therefore, many studies have begun to comprehensively consider the potential of various rib structures in enhancing heat transfer and reducing flow resistance. In the design process of the internal cooling structure of the conventional turbine blade, the rib is placed on the blade, which increases the blade burden. In this paper, the classic rib structure is changed, and the rib is placed on the impingement plate to research its heat transfer characteristics. In this study, the effects of ribs of different structures on heat transfer were tested. Calculate the working conditions of Reynolds number Re = 15000, 20000, 25000, 30000. The numerical calculation of the SST k-w model is used to evaluate the average Nusselt number of the target plate and the flow coefficient of the channel, and the heat transfer distribution and flow field are analyzed. This study is expected to achieve better coordination between improved heat transfer and reduced flow resistance.
Overall Cooling Effectiveness on a Gas Turbine Vane With Swirl-Film Cooling
Authors: Du Haifen , Xie Danmei , Chen Wei , Mei Ziyue , Zhang Jing
Published: November 2019

Numerical calculation of conjugate heat transfer is carried out to study the effect of combined film and swirl cooling at the leading edge of a gas turbine vane with a a cooling chamber inside, in which 3-D steady RANS approach with the k-ω SST turbulence model is used. Two different kinds of coolant chamber configuration (C1 and C2) are selected. In C2, the cooling chamber is composed of a front cavity and a back cavity, and the two cavities are connected by a passage which is divided into 16 segments. The comparative investigations between C1 and C2 cases have been carried out to study the effect of different cooling chambers at M = 0.25, 0.5, 1 and 2. For two cases, overall cooling effectiveness increases with M increasing. In C1 case, with increasing M, differences of mass flow through film holes rows will decrease. The variation of mass flow from holes changes by less than 26.7% at M = 2. However, in C2 case, mass flow through S1 and S2 is significantly larger than that through other film holes rows. Area-averaged overall effectiveness in C2 is larger by 2.5% at M = 0.25 compared to C1 case.
Experimental Rotordynamic Force Coefficients for a Diffusion Bonded Compliant Hybrid Journal Gas Bearing Utilizing Fluid-Filled Hermetic Dampers
Authors: Gary Keith , Ertas Bugra
Published: November 2019

Dynamic force coefficients are presented from experimental results of a radial gas bearing with hermetically sealed squeeze film dampers (HSFD) in the bearing support. HSFDs are a relatively new technology aimed to increase damping levels in gas bearings while sustaining an oil-free bearing sump. Past HSFD designs proved bulky and contained many components making it difficult to employ in size limited environments such as jet engines, while the diffusion bonded bearing discussed in the present paper provides a compact integral design. Test results for a three-inch diameter bearing using a test rig providing static loads up to 80 lbs, controlled-dynamic orbital motion, and speeds up to 27 krpm are shown. Results include frequency and speed dependent direct and cross-coupled rotordynamic force coefficients. Dynamic testing showed little dependence on rotor speed or static load and exhibited frequency dependency at lower excitation frequencies. Cross-coupled terms are generally an order of magnitude lower than direct terms. Results show the direct stiffness coefficients increasing with frequency while direct damping decays radically with frequency. Comparison of the overall gas bearing coefficients with a companion paper [1], showing bearing support coefficients, reveals a drastic reduction in damping when engaging the gas film. The results also indicate the bearing can withstand vibration levels representative of a large rotor system critical speed at lower excitation frequencies.
Working Fluid Selection for a Waste Heat Recovery Organic Rankine Cycle (ORC) Applied to a Petroleum Distillation Process
Authors: Peralta Sergio , Celis Cesar
Published: November 2019

This work describes a working fluid selection process for an ORC based power plant that uses as heat source waste heat from a petroleum distillation furnace. Sixteen (16) organic fluids previously considered for similar applications are analyzed based on environmental, safety and physical properties. Two different power plants layouts, a basic one and another featuring an internal heat exchanger (IHE), are analyzed. The combinations between working fluids and plant layouts seek to maximize the ORC-based power plant thermal efficiency. ORC exergy destruction and exergy efficiency are also accounted for. In this work, the close interrelation between working fluids thermo-physical properties and expander dimensionless characteristics is also assessed. The main results indicate that R245ca and R245fa are the working fluid leading to both the highest thermal (∼16%) and exergy efficiencies (∼23%), and the lowest exergy destructions (∼703 kW). Based on required properties of the selected working fluid, an axial turbine design seems to be the most appropriate ORC expander technology for the particular application discussed in this paper. The outcomes from this work will be used as the basis for the detailed design of the components of an ORC-based power plant focused on increasing the overall efficiency of petroleum distillation processes.
Numerical Study of Heat Transfer in Novel Wavy Trailing Edge Design for Gas Turbine Airfoils
Authors: Parbat Sarwesh , Yang Li , Chyu Minking , Siw Sin Chien , Lee Ching-Pang
Published: November 2019

The strive to achieve increasingly higher efficiencies in gas turbine power generation has led to a continued rise in the turbine inlet temperature. As a result, novel cooling approaches for gas turbine blades are necessary to maintain them within the material’s thermal mechanical performance envelope. Various internal and external cooling technologies are used in different parts of the blade airfoil to provide the desired levels of cooling. Among the different regions of the blade profile, the trailing edge (TE) presents additional cooling challenges due to the thin cross section and high thermal loads. In this study, a new wavy geometry for the TE has been proposed and analyzed using steady state numerical simulations. The wavy TE structure resembled a sinusoidal wave running along the span of the blade. The troughs on both pressure side and suction side contained the coolant exit slots. As a result, consecutive coolant exit slots provided an alternating discharge between the suction side and the pressure side of the blade. Steady state conjugate heat transfer simulations were carried out using CFX solver for four coolant to mainstream mass flow ratios of 0.45%, 1%, 1.5% and 3%. The temperature distribution and film cooling effectiveness in the TE region were compared to two conventional geometries, pressure side cutback and centerline ejection which are widely used in vanes and blades for both land-based and aviation gas turbine engines. Unstructured mesh was generated for both fluid and solid domains and interfaces were defined between the two domains. For turbulence closer, SST-kω model was used. The wall y+ was maintained < 1 by using inflation layers at all the solid fluid interfaces. The numerical results depicted that the alternating discharge from the wavy TE was able to form protective film coverage on both the pressure and suction side of the blade. As a result, significant reduction in the TE metal was observed which was up to 14% lower in volume averaged temperature in the TE region when compared to the two baseline conventional configurations.
Condition Monitoring of Wind Turbine Planetary Gearboxes Under Different Operating Conditions
Authors: Mauricio Alexandre , Sheng Shuangwen , Gryllias Konstantinos
Published: November 2019

Digitally enhanced services for wind power could reduce Operations and Maintenance (O&M) costs as well as the Levelised Cost Of Energy (LCOE). Therefore, there is a continuous need for advanced monitoring techniques which can exploit the opportunities of Internet of Things (IoT) and Big Data Analytics, revolutionizing the future of the energy sector. The heart of wind turbines is a rather complex epicyclic gearbox. Among others, extremely critical gearbox components which are often responsible for machinery stops are the rolling element bearings. The vibration signatures of bearings are rather weak compared to other components, such as gears, and as a result an extended number of signal processing techniques and tools have been proposed during the last decades, focusing towards accurate, early, and on time bearing fault detection with limited false alarms and missed detections. Envelope Analysis is one of the most important methodologies, where an envelope of the vibration signal is estimated usually after filtering around a frequency band excited by impacts due to the bearing faults. Different tools, such as Kurtogram, have been proposed in order to accurately select the optimum filter parameters (center frequency and bandwidth). Cyclic Spectral Correlation and Cyclic Spectral Coherence, based on Cyclostationary Analysis, have been proved as very powerful tools for condition monitoring. The monitoring techniques seem to have reached a mature level in case a machinery operates under steady speed and load. On the other hand, in case the operating conditions change, it is still unclear whether the change of the monitoring indicators is due to the change of the health of the machinery or due to the change of the operating parameters. Recently, the authors have proposed a new tool called IESFOgram, which is based on Cyclic Spectral Coherence and can automatically select the filtering band. Furthermore, the Cyclic Spectral Coherence is integrated along the selected frequency band leading to an Improved Envelope Spectrum. In this paper, the performance of the tool is evaluated and further extended on cases operating under different speeds and different loads. The effectiveness of the methodology is tested and validated on the National Renewable Energy Laboratory (NREL) wind turbine gearbox vibration condition monitoring benchmarking data set which includes various faults with different levels of diagnostic complexity as well as various speed and load operating conditions.
Assessment of Long Term Creep Using Strain Rate Matching From the Stepped Isostress Method
Authors: Mach Robert , Pellicotte Jacob , Haynes Amanda , Stewart Calvin
Published: November 2019

Creep testing is an ongoing need, particularly with the development of new candidate alloy systems for advanced energy systems. The conventional creep test (CT) is regarded as a proven method to gather creep data however, the test is impractical due to being real-time: lasting up to 105 hours to characterize the service of long-lived turbomachinery components. Accelerated methods to gather the long-term creep properties of materials are needed to reduce the time to qualification of new materials. The time-temperature-stress-superposition principle (TTSSP) and the derivative time-temperature superposition principle (TTSP), time-stress superposition principle (TSSP), stepped isothermal method (SIM), and stepped isostress method (SSM) are accelerated creep tests (ACT) commonly used to predict the long-term creep behaviors of polymers and composites. The TTSP and TSSP tests require multiple specimen tested at various temperatures/stresses whereas the SIM and SSM tests employ a single specimen where temperature/stress are periodically step increased until rupture. The stepped creep deformation curve can then be time and strain shifted to produce a master creep curve. While these ACTs are useful tools to predict long-term creep, the drawback is the lack of mathematical laws to determine the virtual start time and time shift factors, especially for different materials.

In this paper, a new self-calibration approach is developed and compared to existing SSM data for Kevlar 49. This new approach focuses on matching the creep strain rates between stress steps and fitting the data to a master curve using a modified theta projection model. This is performed using a MATLAB code consisting of five subroutines. The first subroutine takes the stress, time, and creep strain from SSM/SIM tests, and segregates the data intro arrays corresponding to each stress level. The second subroutine finds the constants for the modified theta projection model for each stress level. The third subroutine performs a time shift adjustment using creep strain rate matching. The fourth subroutine calculates the accelerated time of rupture. The last subroutine generates accelerated creep versus time plots. Kevlar 49 SSM data is gathered from literature and run through the MATLAB code. The master curves generated from the MATLAB are compared to the conventional creep curve of Kevlar 49 as well as the master curve gathered from literature in order to validate the feasibility of this new approach. The goal of this project is to vet if the self-calibration approach can produce results similar to the reference calibration approach.
Modeling of Turbulent Swirl Stabilized Flame With Flamelet Generated Manifold and Hybrid LES-RANS Turbulence Model
Authors: Verma Ishan , Yadav Rakesh , Sharkey Patrick , Li Shaoping , Meeks Ellen
Published: November 2019

Hybrid turbulence modeling is a practical approach to efficiently model the wall-bounded turbulent flows. In this paper, a stress-blended eddy simulation (SBES) model is used with the flamelet generated manifold model (FGM) for modeling turbulent combustion. In the current SBES, the near-wall region is modeled using a two-equation k-ω Reynolds-averaged Navier-Strokes (RANS) formulation, and switches to a large eddy simulation (LES) model in the core region using a blending function. Similarly, the turbulence-related combustion modeling parameters, such as the variances in scalar transport equations and scalar dissipation, are also blended using the same blending function. This combined hybrid FGM-SBES approach is implemented into ANSYS Fluent software and then used to model a swirl-stabilized flame. The flame used is a methane-fueled burner, developed at DLR Stuttgart as the PRECCINSTA combustor. The experimental data for this combustor are available for multiple operating conditions. A stable operating point (φ = 0.83, P = 30 kW) is chosen. The current FGM-SBES results are compared with experimental data as well as with FGM-LES computations. Differences in predictions of mean and variance of reaction progress and mixture fraction in the core versus the near wall region are analyzed and quantified. The impact of the differences in these parameters is then evaluated by comparing temperature and species mass fractions. The findings from the current work, in terms of accuracy, validity and best practices when modeling wall-bounded flows with FGM-SBES are discussed and summarized.
Effects of Fuel Staging on the Hydrodynamic Stability of Multi Nozzle Swirl Flows
Authors: Gupta Saarthak , Manoharan Kiran , Hemchandra Santosh
Published: November 2019

Hydrodynamic instability in lean premixed gas turbine combustors can cause coherent flow velocity oscillations. These can in turn drive heat release oscillations that when favourably coupled with combustor acoustic modes can result in combustion instability. The aim of this paper is to understand the impact of fuel staging on the characteristics of hydrodynamic modes in multi-nozzle combustors. We extend our recent numerical study on the hydrodynamic stability characteristics of a multi-nozzle combustor having three nozzles in a straight line with uniform fuel-air ratio in each nozzle, to the non-uniform fuel-air ratio case. As before we construct the base flow model for this study by super-posing contributions from individual nozzles, determined using a base flow model for a nominally axi-symmetric single nozzle, at every point in the computational domain. The impact of fuel staging is captured by changing the burnt to unburnt gas density ratio parameter in the individual contribution from each nozzle. We investigate the characteristics of the most locally absolutely unstable mode for two cases. The first one is when the middle nozzle is made fuel rich when compared to the side nozzles and the second is when the side nozzles are made fuel rich relative to the middle nozzle. The impact of non-uniform fuel/air ratio on the local absolutely unstable temporal eigenvalues is seen to be small. However, significant changes in the spatial structure of the flow oscillations associated with the hydrodynamic eigen-modes are observed. In the first case, the flow oscillations with a different locally azimuthal nature on the middle nozzle when compared to the side nozzles emerge as the middle nozzle is made richer. In the second case, the oscillations on the two side nozzles are suppressed leaving the middle nozzle in a state that closely matches that of a single unconfined nozzle with the same nominal base flow velocity field. These types of inter-nozzle variations in flow oscillation characteristics can explain the emergence of non-uniformity in heat release oscillation characteristics between individual nozzles in multi-nozzle combustors.
Introduction and Commissioning of the New Darmstadt Transonic Compressor Test Facility
Authors: Kunkel Christian , Werner Jan , Franke Daniel , Schiffer Heinz-Peter , Wartzek Fabian , Biela Christoph , Starke Christoph
Published: November 2019

With the well-known Transonic Compressor Darmstadt (TCD) in operation since 1994, profound knowledge in designing and operating a sophisticated test-rig is available at the Institute of Gas Turbines and Aerospace Propulsion of TU Darmstadt. During this period, TCD has been subject to a vast number of redesigns within different measurement campaigns (see [1], [2], [3], [4], [5], [6], [7], [8]). To expand the capabilities and ensure a sustainable process of compressor research, a new test facility was designed and built by the institute. The new test rig Transonic Compressor Darmstadt 2 (TCD2) features increased power for higher pressure ratios and higher mass-flow, a state of the art control system, increased flexibility towards different compressor geometries and modern data acquisition hardware and software.

Following the successful commissioning of the test-rig in March 2018, a first measurement campaign has been conducted. Early test results regarding aerodynamic performance and aeroelastic effects of the test compressor are presented together with a detailed overview of test-rig infrastructure and control systems as well as the test compressor and the measurement hardware.
High Momentum Jet Flames at Elevated Pressure: Part D — Simultaneous Measurements of OH/PAH PLIF and Mie Scattering on Liquid Fuels
Authors: Schäfer Dominik , Gounder James D. , Lammel Oliver , Ax Holger , Lückerath Rainer , Aigner Manfred
Published: November 2019

A promising alternative to modern swirl combustors for gas turbines are high momentum jet stabilized combustors. This gas turbine burner concept consists of circular arranged jet nozzles through which partially premixed high momentum jets enter the combustion chamber in axial direction. Furthermore, it features fuel flexibility, load flexibility and low pollutant emissions. The investigated generic combustor consists of an eccentric single nozzle in a square chamber. This nozzle represents a full-scale segment of a concentrically arranged multi-nozzle configuration. All measurements were carried out at the high pressure combustion test rig (HBK-S) at the German Aerospace Center (DLR) in Stuttgart.

The generic single nozzle model combustor has been operated in a high-pressure test rig with large optical access in order to gain a detailed understanding of fuel distribution, droplet distribution, fuel air mixing and high temperature regions through various sections of the combustion chamber. For this purpose, different laser based measurement techniques have been applied simultaneously under gas turbine relevant conditions on liquid fuels (oil and oil/water). Other measurements in this combustor on gaseous fuels were presented in preceding (parts A and B) and current publications (part C).

Mie scattering was used to visualize the liquid phase of oil and water downstream of the nozzle. In order to gain knowledge about the droplet velocity, a Nd:YAG double pulse laser at 532 nm was used for Particle Image Velocimetry (PIV). Additionally the gaseous and liquid phases of oil have been visualized through Planar Laser Induced Fluorescence (PLIF) by excitation of poly-cyclic aromatic hydrocarbons (PAHs) with a laser wavelength of 266 nm. To observe high temperature regions, OH and PAH PLIF was also performed with a low bandwidth at 283 nm from a Nd:YAG pumped dye laser.

It was possible to separate the low-intensity OH signal of the hot gas regions from the PAH signal by collecting the different LIF signals simultaneously through a dual camera setup. Instantaneous PAH LIF images of the liquid and gaseous phase were compared with Mie scattering images for a qualitative impression of the evaporation. For this a structural comparison between the liquid phases of both images has been carried out. Results indicate, that the evaporation of most of the liquid fuel takes place near the hot gas region, as a large proportion of droplets are carried far downstream of the nozzle by the high momentum jet.
Influence of Tip Shroud Modeling on the Flutter Stability of a Low Pressure Turbine Rotor
Authors: Pinelli Lorenzo , Vanti Federico , Arnone Andrea , Beßling Benjamin , Vogt Damian M.
Published: November 2019

Since the modern design trend of low pressure turbine blades for aeronautical propulsion leads to lighter and more loaded blades, thus prone to flutter induced vibrations; flutter assessment is now a standard verification within the design loop of these components. Flutter stability assessment requires FEM and CFD tools able to predict the pressure response of fluid flow due to blade oscillation in order to compute the aerodynamic damping. Such tools are mature and validated, yet some geometrical aspects of the blade-row as contact interfaces at the blade tip shroud have to be carefully simulated to obtain accurate flutter results. The aim of this paper is to demonstrate the capability of the Open Source FEM tool (CalculiX) to deal with complex interlocked rotor geometries when performing modal analysis and to show the influence of different contact interface modeling on flutter stability. The solid mesh of a single-pitch row sector has been generated by using the Open Source suite Salome and the modal analysis has been carried out with CalculiX with cyclic symmetry conditions. The following uncoupled flutter simulations have been performed with the CFD TRAF code, an in-house solver developed at the University of Florence, which implements a non-linear method for flutter evaluation. An in-depth comparison among the FEM models with different boundary conditions in terms of mode shape frequency and aerodynamic damping curves are reported. These results show the effect of different contact interface models, especially on the first bending mode family, and confirm the overall row stability detected during a dedicated experimental flutter campaign.
Thermal Optimization of Air Foil Thrust Bearings Using Different Foil Materials
Authors: Rieken Markus , Mahner Marcel , Schweizer Bernhard
Published: November 2019

Air foil bearings are used in turbomachinery applications with high speeds and in oil-free environments. Their numerical analysis has to account for the multiphysicality of the problem. This work features a detailed thermo-elasto-hydrodynamic model of an air foil thrust bearing with bump-type foil-structure. The bearing geometry is designed to produce a high load capacity while maintaining thermally stable conditions. The presented model considers foil deformations using a Reissner-Mindlin-type shell theory. Dry friction (stick-slip approach) between the top foil, the bump foil and the base plate is taken into account in the model. Reynolds equation from lubrication theory is used to study the hydrodynamic behavior of the air film. A thermal model of the lubricating gap, the foil sandwich and the rotor disk including heat fluxes into the rotor and the periphery as well as a cooling flow on the backside of the rotor disk are presented. Elastic deformations of the rotor disk due to centrifugal effects are calculated; deformations caused by temperature gradients are investigated as well. In air foil thrust bearings, very high temperatures are often observed and a forced cooling flow through the foil sandwich has to be applied. Using a cooling flow by applying a pressure difference between the inner and outer radius of the thrust bearing has several drawbacks: the additional cooling flow reduces the overall efficiency of the machine and requires additional constructive measures. In this work, a passive cooling concept is analyzed, where the typical steel foils are replaced with other materials, which have a significantly higher thermal conductivity. The simulation results show that the bearing temperatures can be reduced markedly (up to 70°C in the considered test case) by this approach.
Nonlinear Harmonic Analysis of a Blade Model Subjected to Large Geometrical Deflection and Internal Resonance
Authors: Di Palma Nicolas , Martin Adrien , Thouverez Fabrice , Courtier Vivien
Published: November 2019

This paper is devoted to the study of the nonlinear harmonic response of an industrial blade model subjected to large geometrical deflection. A reduction procedure is performed on the blade model using the linear normal modes of the structure. Geometrical nonlinear effects are taken into account by considering cubic and quadratic stiffnesses in the dynamical reduced model. Reduced nonlinear stiffness coefficients are computed with the STiffness Evaluation Procedure (STEP) and periodic solutions are sought using the Harmonic Balance Method (HBM) coupled to a pseudo-arclength continuation. Along with the harmonic response, a bifurcation analysis is performed to compute both turning and branching points. Specific attention is paid to the internal resonance phenomenon. 2 to 1 internal resonance occurred during the frequency response analysis close to the first and second modes of the reduced model. Mode coupling phenomena occurred during the harmonic analysis and secondary branches of solutions were obtained from branching point bifurcations.
Probabilistic FE-Analysis of Cooled High Pressure Turbine Blades: Part B — Probabilistic Analysis
Authors: Högner Lars , Voigt Matthias , Mailach Ronald , Meyer Marcus , Gerstberger Ulf
Published: November 2019

Modern high pressure turbine (HPT) blade design stands out due to high complexity comprising three-dimensional blade features, multi-passage cooling system (MPCS) and film cooling to allow for progressive thermodynamic process parameters. During the last decade, probabilistic design approaches have become increasingly important in turbomachinery to incorporate uncertainties such as geometric variations caused by manufacturing scatter.

In part B of this two-part paper, real geometry effects are considered within a probabilistic finite element (FE) analysis that aims at sensitivity evaluation. The knowledge about the geometric variability is derived based on a blade population of more than 400 individuals by means of parametric models that are introduced in part A (cf. Högner et al. [1]). The HPT blade population is statistically assessed which allows for reliable sensitivity analysis and robustness evaluation taking the variability of the airfoil, profiled endwalls (PEW) at hub and shroud, wedge surfaces (WSF) and the MPCS into account.

The probabilistic method — Monte-Carlo simulation (MCS) using an extended Latin Hypercube Sampling (eLHS) technique — is presented subsequently. Afterwards, the FE model that involves thermal, linear-elastic stress and creep analysis is described briefly. Based on this, the fully automated process chain involving CAD model creation, FE mesh morphing, FE analysis and post-processing is executed. Here, the mesh morphing process is presented involving a discussion of the mesh quality. The process robustness is assessed and quantified referring to the impact on input parameter correlation.

Finally, the result quantities of the probabilistic FE simulation are evaluated in terms of sensitivities. For this purpose, regions of interest are determined, wherein the statistical analysis is conducted to achieve the sensitivity ranking. A significant influence of the considered geometric uncertainties onto mechanical output quantities is observed which motivates to incorporate these in modern design strategies or robust optimization.
Recognition of Structures Leading to Transition in a Low Pressure Turbine Cascade: Effect of Reduced Frequency
Authors: Lengani D. , Simoni D. , Ubaldi M. , Zunino P. , Bertini F.
Published: November 2019

The boundary layer developing over the suction side of a low pressure turbine cascade operating under unsteady inflow conditions has been experimentally investigated. Time-resolved Particle Image Velocimetry (PIV) measurements have been performed in two orthogonal planes, the blade to blade and a wall parallel plane embedded within the boundary layer, for two different wake reduced frequencies. Proper Orthogonal Decomposition (POD) has been used to analyze the data and to provide an interpretation of the most significant flow structures for each phase of the wake passing cycle. To this purpose, a POD based procedure that sorts the data synchronizing the measurements of the two planes has been developed. Phase averaged data are then obtained for both cases. Moreover, once properly sorted, POD has been applied to sub-ensembles of data at the same relative phase within the wake passing cycle. Detailed information on the most energetic turbulent structures at a particular phase are obtained with this procedure (called phased POD), overcoming the limit of classical phase average that just provides a statistical representation of the turbulence field. Furthermore, the synchronization of the measurements in the two planes allows the computation of the characteristic dimension of boundary layer structures that are responsible for transition. These structures are often identified as vortical filaments parallel to the wall, typically referred to as boundary layer streaks.

The largest and most energetic structures are observed when the wake centerline passes over the rear part of the suction side, and they appear practically the same for both reduced frequencies. The passing wake forces transition leading to the breakdown of the boundary layer streaks. Otherwise, the largest differences between the low and high reduced frequency are observed in the calmed region. The post-processing of these two planes further allowed us to compute the spacing of the streaks and make it non-dimensional by the boundary layer displacement thickness observed for each phase. The non-dimensional value of the streaks spacing is about constant, irrespective of the reduced frequency.
A Steady State Thermal Prediction Method for Ship Board Turbocharger and its Validation With Experiments
Authors: Ohuchida Satoshi , Seo Satoshi , Okita Yoji
Published: November 2019

The present study aims to develop prediction method of turbocharger’s turbine wheel temperature at working conditions. To take fluid-solid heat transfer physics into account, CHT (Conjugate Heat Transfer) based approach is introduced. The model mesh comprises turbine wheel, rotor shaft, and stationary parts of the turbine side together with internal fluid region. Remaining parts, compressor or surrounding atmosphere are not included in the calculation mesh yet boundary conditions at contact surface of the outer mesh region were carefully considered and coupled into CHT.

An actual ship board turbocharger was selected to investigate presented calculation method. Multiple point thermal measurement was conducted both for the turbine wheel and the stationary parts to obtain verification data. CHT calculation for this model case was demonstrated and results were compared. The results, especially at the rotor wheel surface shows fairly good agreement with the measured temperatures within the range of ± 5degC. Stationary part temperatures showed larger discrepancy yet high/low relationship of temperatures from parts to parts was agreed with the experiment. The reason for temperature discrepancy was considered to come from too simplified modeling of heat transfer path and this can be improved in future work.
Inlet Turbulence and Off-Design Incidence Response of High Efficiency, Turbine OGV Profiles
Authors: Lazaro Benigno J. , Gonzalez Ezequiel , Parra Jorge , Robles David Cadrecha
Published: November 2019

In spite of advances in CFD prediction tools, the current design of outlet guide vane (OGV) stages for flow recovery downstream from low pressure turbines (LPT) still has to face significant flow entrance uncertainties. To ensure proper response of modern, high efficiency OGV’s, the sensitivity in the aerodynamic response of the vanes to both different levels of inlet turbulence and off-design incidence must be analyzed. To that end, a systematic experimental investigation of a current design LPT OGV airfoil has been undertaken in a low-speed linear cascade. Wall pressure distributions as well as high-resolution total pressure drop and LDV measurements have been used to determine the flow response. The experimental facility includes different boundary suction strategies for proper control of flow periodicity and endwall effects at significant off-design incidences. In addition, different inlet grids to promote an entrance flow having controlled isotropic background turbulence are included. The experimental flow response of the OGV airfoil is presented for a wide range of Reynolds numbers and different values of the inlet flow incidence and turbulence properties. Both at design and off-design incidences, different flow regimes and performance degradation mechanisms are discussed. In addition, the effect of inlet turbulence at close to design incidence is discussed, with the experimental evidence suggesting that its effect can be described by defining a properly scaled Reynolds number. The ability of CFD simulations based on currently available RANS transition models to describe the flow in high efficiency turbine OGV airfoils is finally explored.
Improving Emission and Blow-Out Characteristics of Novel Natural Gas Low NOx Burners for Heavy Duty Gas Turbine
Authors: Cerutti Matteo , Roma Michele , Picchi Alessio , Becchi Riccardo , Facchini Bruno
Published: November 2019

The development and the optimization of a novel dry low NOx burner may require several steps of improvement.

The first step of the overall development process has been documented by authors in a previous paper and included an exhaustive experimental characterization of a set of novel geometries. The in-depth results analysis allowed to correlate the investigated design parameters to burner performances, discovering possible two-fold optimization paths.

Recurrent verifications of the assumptions made to define prototypes design are considered a mandatory step to avoid significant deviation from the correct optimization path, which strongly depends on both objective function definition and selection of design variables.

Concerning the objective function, a proper mathematical formulation was proposed in the previous work, which represented a balance between two apparently conflicting aspect like flame stability and low emissions.

Concerning design variables, outcomes of the first test campaign have been used in the present work to define new burner geometries. Starting from a new baseline who has showed the widest low NOx operating window, additional geometrical features have been considered in this survey as potentially affecting flame stabilization. Thanks to the degree of freedom offered by DMLM technology, rapid prototyping of alternative geometries allowed to easily setup a new experimental plan for the second optimization step.

Exploiting the same approach used in the first test campaign, new geometries have been tested in a single-cup test rig at gas turbine relevant operating conditions, showing

Stable low-NOx operating windows have been evaluated throughout dedicated objective functions for all geometries and results showed lower NOx and CO emissions as a consequence of the newly introduced geometrical modifications.

Moreover, the comparison with the estimates of the previous campaign proved the existence of the identified optimization path. Indeed, it furnished valid elements for further using of the proposed methodology for the improvement of emission and blow-out characteristics of novel burners and, more in general, for the development of a novel dry low NOx technology.
The Effect of Local Casing Features and External Dummy Flanges on Casing Contraction for Thermal Control of Blade Tip Clearance
Authors: Choi Myeonggeun , Gillespie David R. H.
Published: November 2019

Thermal closure of the engine casing is widely used to minimise undesirable blade tip leakage flows and thus improve jet engine performance. While this may be achieved using an external cooling scheme on the casing wall, the geometry of the casing itself may have considerable influence on the contraction. In this paper, key controllable design parameters such as the thickness of the casing, the extent (radial height) of the annular dummy flanges and their axial position have been examined to identify how the geometric features may be manipulated to obtain an optimised system for both contraction and weight. Finite element modelling has been used to simulate the contraction of a range of casing geometries using external cooling schemes, adapted previous work by the authors. The displacement-coolant exchange rate of each casing configuration is reported in mm / kg s−1. The results show the relative sensitivity of the contraction of the engine casing to the casing thickness, the radial height, and thickness profiling of the flanges, and also to the balance between jets impinging on the casing and towards the root of the flanges.
Combustion Instabilities Damping System Development for Dry Low NOx Emissions Operability Enhancement of a Heavy-Duty Gas Turbine
Authors: Cerutti Matteo , Giannini Nicola , Schuermans Bruno , Brenci Riccardo , Marini Alessandro , Ceccherini Gianni , Riccio Giovanni
Published: November 2019

This paper describes the development phases of a damping system for combustion instability reduction in an annular type combustor for heavy-duty gas turbine applications. As reported by the authors in a previous paper, the full scale annular test rig allowed for an extensive characterization of the combustor with realistic acoustic boundaries at engine-relevant conditions. Emissions and operability assessment over a wide range of load conditions was performed, allowing the evaluation of the response of the system near the thermo-acoustic instability onset.

The instability is quantified by its acoustic growth rate. This quantity is a crucial input in the design process of dampers. A methodology has been used to extract these growth rates form measured pulsation data.

Experimentally determined growth rates have been evaluated for different fuel flow rate split between the main and the pilot injections, providing input to dampers preliminary design. Given current combustor architecture constraints, a first attempt configuration has been proposed and performances evaluated in the full annular rig. Dampers have been equipped with dynamic sensors and thermocouples with the purpose of measuring the growth rate abatement and the consequent NOx emissions reduction. A dedicated numerical toolbox, in-house developed by GE Power, has been used for both dampers preliminary design and growth rate reduction evaluation. Fine tuning of dampers elements as well as design assumptions adjustments required additional experimental evaluations and design iterations.

Encouraged by the successful test in the concept phase, an optimized design for engine implementation was defined, that featured a significant increased damper volume, involving combustor parts re-design. The optimized configuration was finally tested in full annular rig and results demonstrated an important enhancement of operability while maintaining NOx emissions below the target levels.
Robust Active Flow Control of a Stator Cascade With Integer Control Functions and Sum-Up Rounding
Authors: Neuhäuser Karl , King Rudibert
Published: November 2019

This work is part of a research initiative that aims at increasing the overall gas turbine efficiency by means of constant volume combustion (CVC). For that purpose, flow control in the compressor becomes important, since unsteady combustion effects that may occur in a CVC are very likely to affect stability and efficiency of the compressor negatively due to flow disturbances.

Active Flow Control (AFC) often has to deal with uncertain flow conditions, e.g., due to turbulence, varying operating ranges, or simply environmental effects. By that, system parameters such as gain or time constants of the system model also become uncertain, making it difficult for control algorithms to ensure optimality or even stable behavior. Robust control in the sense of ℋ∞ control tackles these problems using an uncertainty description and a nominal model of the system. In this contribution, robust control applied to a linear stator cascade is addressed when only a binary control output from solenoid valves is available. Moreover, a surrogate control variable is proposed, describing the extent of the velocity deficit. By means of a principal component analysis, this control variable is reconstructed from a single measurement input.

AFC is realized via trailing edge blowing. In comparison to proportional valves, solenoid valves are cheaper and offer faster switching times with the drawback of a restricted range of the control output to integer or even binary values. Since the ℋ∞ controller, as well as most other control algorithms, results in a real-valued signal u(t) ∈ ℝ, a sum-up rounding strategy is applied to the controller output, forming a binary control output ub (t) ∈ {0, 1}. Although it is impossible for the two outputs to completely match, unless both are integer-valued, there is proof that the difference of real-valued to binary output is bounded in its integral value. The investigations show that a switching frequency of the valves of 100 Hz is sufficient to ensure that the control error via binary control matches its expected equivalent via real-valued control for the presented system.
Simultaneous TR-PIV and CH* Chemiluminescence During Combustion-Instability Triggered Flame-Flashback in a Backward Facing Step Combustor
Authors: Pancharia Pankaj , Ramanan Vikram , Nagarajan Baladandayuthapani , Chakravarthy S. R.
Published: November 2019

The present study is an experimental investigation of the nature of acoustically induced flashback in a lab-scale dump combustor. The control parameters varied include the inlet Reynolds number (Re) and the inlet turbulence intensity. The primary bifurcation plots of the combustor from stable to the unstable condition are seen to be significantly altered by the inlet turbulence intensity, with the latter delaying the onset of combustion instability to higher Re. The analysis of multivariate high-speed data acquisition and processing (viz. unsteady pressure, flame imaging and velocity field by means of PIV) reveals the role of low-frequency high amplitude acoustics in modulating the flame. It is seen that high amplitude oscillations are sustained by two mechanisms 1. Modulation of the flame by coherent structures shedding at the step and 2. The bulk flame motion in-and-out at the edge of the step. It is seen that flow reversal at sufficiently low frequencies provide enough duration for the hot products to ignite fresh reactants upstream of the duct, which in-turn reinforces the coherent unsteadiness in the system, thereby increasing the propensity of the mixture to be ignited more upstream with every cycle. This ultimately leads to the flame flashing back till the point of premixing. This work thus addresses and reforms the occurrence of flashback being an example of loss of static stability, whereby the overriding presence of dynamic combustion instability results in a flashback to behave in a dynamic manner.