bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical and Experimental Investigations for Flow Fields Under Non-Reacting and Reacting Conditions Through a Lean Premixed Fuel Nozzle
Authors: Kedukodi Sandeep , Park Suhyeon , Gadiraju Siddhartha , Ekkad Srinath , Kim Yong , Srinivasan Ram
Published: August 2017

Numerical methods coupled with experimental benchmarking approaches, are typically used as effective tools for solving engineering problems due to their significant time saving benefits. In this paper, the swirling flow through an industrial lean-premixed fuel nozzle as used in actual gas turbine combustors is numerically analyzed and compared with experimental observations. The analysis is performed under both non-reacting and reacting conditions for a specific Reynolds number. The reacting experiments were performed using compressed methane as the fuel and air as the oxidizer. A specific inlet Reynolds number flow was studied to understand the combustor flow field with an overall equivalence ratio of 0.65 and 6% pilot fuel.

Steady state simulations were performed using Fluent solver using Realizable k-ε turbulence model. The reacting flow was simulated using Flamelet Generation Manifold (FGM) model to simulate partially premixed combustion. The non-reacting simulations predicted the combustor flow profiles with certain deviation from Particle Image Velocimetry (PIV) data within the central recirculation region. This deviation may be attributed to the inherent limitations of turbulence model in predicting the central vortex accurately. However, the simulated flow fields were in very good agreement with PIV data under reacting conditions. Additionally, the study was also extended to investigate the sensitivity of inlet swirl on the jet impingement location along the combustor wall. It was found that reaction significantly modifies the jet impingement location for lower inlet swirl angles and showed negligible impact under non-reacting conditions.

The presented studies in this paper provide a comprehensive summary of modified flow features under non-reacting and reacting conditions and also demonstrates the sensitivity of inlet swirl changes on the location of liner wall impingement. This study is believed to offer a strong base for future studies involving heat transfer characterization along the combustor walls under reacting conditions; and also provide valuable information to the gas turbine combustor design community towards improved liner wall designs using simplistic numerical modeling approaches.
Modelling Impingement-Effusion Flow Inside Double-Walled Combustor Tile
Authors: Ammour Dalila , Page Gary J.
Published: August 2017

The prediction of temperature and heat transfer throughout the solid material of a gas-turbine combustor has driven interest in cooling technology which uses impingement/effusion (IE) cooling tiles on double-skinned combustor liners. The design of the IE tile system is simple but the aerodynamics are complex. The complexity of flow curvature, combined impingement and effusion cooling and heat transfer, poses a challenge to standard RANS CFD modelling. The IE combustor tile is numerically investigated using both URANS model with the SST-SAS model and Large Eddy Simulation (LES) in the Rolls-Royce in-house CFD code. The aim is to provide accurate CFD data and to test the viability of URANS approach to predict the impingement/effusion flow. Results of pressure, velocity and turbulence quantities are presented. It is found that the SST-SAS model, with high grid resolution, shows good agreement with LES. The current CFD results are used to resolve a substantial amount of very small impingement and effusion holes. The CFD results showed that every feature of the geometry has to be resolved by the numerical mesh, which makes the simulation impractical due to time consuming and high mesh resolution. These cooling holes can be omitted from the computational mesh and their effects captured on the flow via an impingement-effusion (IE) model which is based on defining the correct mass flow inside the holes as a function of the difference of pressure in the upstream and downstream regions of both impingement and effusion regions. The latter model takes the effect of pressure and velocity and it will be extended in future to take into account the heat transfer effects. The IE model is tested and validated for the 3-D combusor tile and results of pressure showed good agreement with the LES data.
Internal and External Cooling of a Full Coverage Effusion Cooling Plate: Effects of Double Wall Cooling Configuration and Conditions
Authors: Ren Zhong , Vanga Sneha Reddy , Rogers Nathan , Ligrani Phil , Hollingsworth Keith , Liberatore Frederico , Patel Rajeshriben , Srinivasan Ram , Ho Yin-hsiang
Published: August 2017

The present study provides new heat transfer data for both the surfaces of the full coverage effusion cooling plate within a double wall cooling test facility. To produce the cooling stream, a cold-side cross-flow supply for the effusion hole array is employed. Also utilized is a unique mainstream mesh heater, which provides transient thermal boundary conditions, after mainstream flow conditions are established. For the effusion cooled surface, presented are spatially-resolved distributions of surface adiabatic film cooling effectiveness, and surface heat transfer coefficients (measured using infrared thermography). For the coolant side, presented are spatially-resolved distributions of surface Nusselt numbers (measured using liquid crystal thermography). Of interest are the effects of streamwise development, blowing ratio, and Reynolds number. Streamwise hole spacing and spanwise hole spacing (normalized by effusion hole diameter) on the effusion plate are 15 and 4, respectively. Effusion hole diameter is 6.35 mm, effusion hole angle is 25 degrees, and effusion plate thickness is 3 hole diameters. Considered are overall effusion blowing ratios from 2.9 to 7.5, with subsonic, incompressible flow, and constant freestream velocity with streamwise development, for two different mainstream Reynolds numbers. For the hot side (mainstream) of the effusion film cooling test plate, results for two mainflow Reynolds numbers of about 145000 and 96000 show that the adiabatic cooling effectiveness is generally higher for the lower Reynolds number for a particular streamwise location and blowing ratio. The heat transfer coefficient is generally higher for the low Reynolds number flow. This is due to altered supply passage flow behavior, which causes a reduction in coolant lift-off of the film from the surface as coolant momentum, relative to mainstream momentum, decreases. For the coolant side of the effusion test plate, Nusselt numbers generally increase with blowing ratio, when compared at a particular streamwise location and mainflow Reynolds number.
Convective Scaling of Intrinsic Thermo-Acoustic Eigenfrequencies of a Premixed Swirl Combustor
Authors: Albayrak Alp , Steinbacher Thomas , Komarek Thomas , Polifke Wolfgang
Published: August 2017

For velocity sensitive premixed flames, intrinsic thermoacoustic (ITA) feedback results from flow-flame-acoustic interactions as follows: perturbations of velocity upstream of the flame result in modulations of the heat release rate, which in turn generate acoustic waves that travel in the downstream as well as the upstream direction. The latter perturb again the upstream velocity, and thus close the ITA feedback loop. This feedback mechanism exhibits resonance frequencies that are not related to acoustic eigenfrequencies of a combustor and generates — in additional to acoustic modes — so-called ITA modes. In this work spectral distributions of the sound pressure level (SPL) observed in a perfectly premixed, swirl stabilized combustion test rig are analyzed. Various burner configurations and operating points are investigated. Spectral peaks in the SPL data for stable as well as for unstable cases are interpreted with the help of a newly developed simple criterion for the prediction of burner intrinsic ITA modes. This criterion extends the known −π measure for the flame transfer function (FTF) by including the burner acoustic. This way, the peaks in the SPL spectra are identified to correspond to either ITA or acoustic modes. It is found that ITA modes are prevalent in this particular combustor. Their frequencies change significantly with the power rating (bulk flow velocity) and the axial position of the swirler, but are insensitive to changes in the length of the combustion chamber. It is argued that the resonance frequencies of the ITA feedback loop are governed by convective time scales. For that reason, they arise at rather low frequencies, which scale with the bulk flow velocity.
Experimental Investigation of Numerically Optimized Wavy Microchannels Created Through Additive Manufacturing
Authors: Kirsch Kathryn L. , Thole Karen A.
Published: August 2017

The increased design space offered by additive manufacturing can inspire unique ideas and different modeling approaches. One tool for generating complex yet effective designs is found in numerical optimization schemes, but until relatively recently, the capability to physically produce such a design had been limited by manufacturing constraints.

In this study, a commercial adjoint optimization solver was used in conjunction with a conventional flow solver to optimize the design of wavy microchannels, the end use of which can be found in gas turbine airfoil skin cooling schemes. Three objective functions were chosen for two baseline wavy channel designs: minimize the pressure drop between channel inlet and outlet, maximize the heat transfer on the channel walls and maximize the ratio between heat transfer and pressure drop. The optimizer was successful in achieving each objective and generated significant geometric variations from the baseline study.

The optimized channels were additively manufactured using Direct Metal Laser Sintering and printed reasonably true to the design intent. Experimental results showed that the high surface roughness in the channels prevented the objective to minimize pressure loss from being fulfilled. However, where heat transfer was to be maximized, the optimized channels showed a corresponding increase in Nusselt number.
Characterization of Spray Formed by Diesel-Water Mixture Jet Injected Into an Air Crossflow
Authors: Song Jinkwan , Lee Jong Guen
Published: August 2017

Using a mixture of water and diesel fuel is considered a way to reduce gas emissions including NOx and COx in the gas turbine. This paper presents experimental results on spray characteristics of the water-diesel fuel mixture in an air crossflow. A plain-orifice type injector of 0.508 mm in diameter is employed in the research. Pure water, pure diesel fuel, and water-diesel fuel mixtures with different mixing ratios are used to compare their spray characteristics. In order to observe spray behaviors in different breakup regimes, Weber numbers for water of 30 and 125 are chosen as the operating condition and the corresponding Weber numbers for diesel fuel at the same conditions are 92 and 382, respectively. Momentum flux ratios are 10 and 20. A tee connection and a subsequent static mixer are employed at upstream of fuel injector to mix two liquids. Phase Doppler Particle Analyzer (PDPA) measurement is performed to measure droplet distributions and mean drop size at various mixture ratios, and planar laser induced fluorescence (PLIF) technique with dyeing either diesel or water is used to look into the primary breakup process. PDPA data show that the spray characteristics of water-diesel fuel mixtures such as mean drop size and number density distribution can be predicted from the measured drop size distribution of pure fluids by weighting those quantities by mass fraction of each fluid, indicating that the water and diesel are injected alternately without significant mixing between the two fluids. A short transition of liquid flow from water-to-diesel or diesel-to-water produces small fraction of relatively bigger droplets.
Effects of Metal Surface Temperature on Deposition-Induced Flow Blockage in a Vane Leading Edge Cooling Geometry
Authors: Whitaker Steven M. , Lundgreen Ryan K. , Bons Jeffrey P.
Published: August 2017

In this study, the effect of the external metal temperature on flow blockage development in a simplified vane leading edge with impingement was assessed. Nominal 0–10 μm Arizona Road Dust particulate was fed into an 866K flow leading to the test article. An electric kiln was used to vary the external surface temperature of the article from 920K to 1262K. The time history of flow blockage development at a constant pressure ratio of 1.031 was recorded for each test. Mass-normalized blockage values at the end of the tests indicate a linear relationship with the external surface temperature, with values at 1262K more than double those at 920K. External surface temperatures were recorded throughout the test period via a surface mounted thermocouple and infrared thermography, indicating an increase in surface temperature proportional to the reduction in mass flow through the part. Localized flow temperature increases highlight areas where internal deposition is most aggressive during the dust injection process. Images of the deposit formations within the test article indicate regions where deposition has the strongest influence on flow blockage development, namely in and around the impingement holes. An analysis of the experiment was also performed using a computational simulation of the flow within the test article. Conjugate heat transfer simulations allow the internal flow and surface temperatures to be assessed for the various test conditions which, along with predicted particle rebound and deposit locations, lend insight into the mechanisms behind the deposition trends observed in the experiments.
Implementing Full Electric Turbocharging Systems on Highly Boosted Gasoline Engines
Authors: Zhang Q. , Lu P. , Dimitriou P. , Akehurst S. , Copeland C. , Zangeneh M. , Richards B. , Fowler G.
Published: August 2017

To secure the highly challenging 2°C climate change limit, the automotive sector is expected to further improve the efficiency of the internal combustion engines. Over the past decade, internal combustion engine downsizing through turbocharging has become one of the major solutions that the industry has offered to fulfil its carbon commitment. Although the various new turbocharging technologies has changed the sluggish image of conventional turbocharged engines, the turbocharger system is far from perfect. From the perspective of engine energy flow, the copious amount of waste energy is habitually harvested by the turbine with low efficiency, subsequently the turbine power transmitted to the compressor is used solely to charge the engine. When this power for charging is excessive for the set engine operating condition, it either is consumed by throttling or is directly discharged through the wastegate, both as a pure enthalpy loss. To more efficiently harness the waste energy without deteriorating other engine performance parameters, a full electric turbocharging technology is proposed by Aeristech Ltd. The system is composed of an electric turbo generator and an electric compressor connected only through electrical system. Without the constraint of a mechanical turboshaft, the compressor and the turbine can be operated at different speeds. The electrically driven compressor can be free floating when boost is not required and the motor can provide the boost promptly only when higher load is requested. Meanwhile, the electric turbine can be controlled by the generator to operate at any set speed, allowing maximum efficiency for energy harvesting. This paper presents a simulation study of the capability of the decoupled eTurbocharging system to charge a highly boosted 2 litre gasoline engine. The single stage eTurbocharger configuration and the eTurbocharger plus a mechanical turbocharger configuration were evaluated and compared. The simulation results have revealed that the two stage eTurbocharging system has the potential to reduce CO2 emission in the proximity of 1 percent in different drive cycles compared to conventional wastegate turbocharger and the benefit would be much higher for future real world driving cycle. The single stage configuration was shown to be impractical in that the power level of the turbine generator will not only limit the engine power output, but also have negative impact on the system design, cooling and cost implied. Meanwhile, the two stage configuration where the eCompressor acts as a supplementary boost device at low end and transient device came out as a better solution with overall advantage in manageable power level, system efficiency, transient response and implied cost.
Dynamic Similarity in Turbine Deposition Testing and the Role of Pressure
Authors: Sacco C. , Bowen C. , Lundgreen R. , Bons J. P. , Ruggiero E. , Allen J. , Bailey J.
Published: August 2017

The role of absolute pressure in deposition testing is reviewed from first principles. Relevant dimensionless parameters for deposition testing are developed and dynamic similarity conditions are assessed in detail. Criteria for establishing appropriate conditions for laboratory studies of deposition are established pursuant to the similarity variables. The role of pressure is particularly singled out for consideration relative to other variables such as temperature, particle size, and test article geometry/scaling. A case study is presented for deposition in a generic array of impinging jets. A fixed quantity (2g) of 0–10micron Arizona Road Dust (ARD) is delivered to the impingement array at three different temperatures (290, 500, and 725K) and at fixed pressure ratio. Deposition results are presented for operating pressures from 1 to 15atm. Surface scans show that the height of deposit cones at the impingement sites decreases with increasing pressure at constant temperature and pressure ratio. This reduction is explained by the lower “effective” Stokes number that occurs at high particle Reynolds numbers, yielding fewer particle impacts at high pressure. A companion CFD study identifies the additional role of Reynolds number in both the impingement hole losses as well as the shear layer thickness.
An Autonomous Uncertainty Quantification Method for the Digital Age: Transonic Flow Simulations Using Multivariate Padé Approximations
Authors: Ahlfeld Richard , Carnevale Mauro , Salvadori Simone , Montomoli Francesco
Published: August 2017

There is a need to automate stochastic uncertainty quantification codes in the digital age. Problems in turbomachinery Computational Fluid Dynamics (CFD) are characterised by non-linear and discontinuous responses and long run times. Ensuring the reliability of Uncertainty Quantification (UQ) codes in such conditions, in an autonomous way, is a challenging problem. Human involvement has always been required. In this work, we therefore suggest a new approach that combines three state-of-the-art methods: multivariate Padé approximations, Optimal Quadrature Subsampling and Statistical Learning.

Its main component is the generalised least squares multivariate Padé-Legendre (PL) approximation. PL approximations are globally fitted rational functions that can accurately describe discontinuous non-linear behaviour. They need fewer model evaluations than local or adaptive methods and do not cause the Gibbs phenomenon, like continuous Polynomial Chaos methods.

We describe a series of modifications of the Padé algorithm that allow us to apply it to arbitrary input points instead of optimal quadrature locations. This property is particularly useful for industrial applications, where a database of CFD runs is already available, but not in optimal parameter locations. One drawback of the PL approximation is that it is non-trivial to ensure reliability for multiple input parameters. We therefore suggest a new method to improve stability in this work: Optimal Quadrature Subsampling. Our argument is that least squares errors, caused by an ill-conditioned design matrix, are the main source of error. Finally, we use statistical learning techniques to automatically guarantee smoothness and convergence.

The resulting method is shown to efficiently and correctly fit thousands of partly discontinuous response surfaces for an industrial film cooling and shock interaction problem automatically and using only 9 CFD simulations. It can be applied to any other UQ problem that is characterised by a limited amount of data and the presence of discontinuities.
Resonance Frequency Detuning With Application Towards Blade Mistuning
Authors: Lopp Garrett K. , Kauffman Jeffrey L.
Published: August 2017

This paper extends the Resonance Frequency Detuning vibration reduction approach by analyzing the performance in cases of turbomachinery blade mistuning. A lumped parameter mistuned blade model with included piezoelectric elements is utilized and an analytical solution for frequency sweep excitation is presented and validated using direct numerical integration. A Monte Carlo statistical analysis is then conducted to provide insight regarding vibration reduction performance over a range of parameters of interest such as the degree of blade mistuning, linear excitation sweep rate, damping ratio, and the difference between the open- and short-circuit stiffness states. Vibration reduction is shown to exist across all degrees of blade mistuning as well as the entire range of sweep rates tested. This vibration reduction performance is also maximized for systems with low inherent damping and large electromechanical coupling values.
CO and H2O Time-Histories in Shock-Heated Blends of Methane and Ethane for Assessment of a Chemical Kinetics Model
Authors: Mathieu O. , Mulvihill C. , Petersen E. L. , Zhang Y. , Curran H. J.
Published: August 2017

Methane and ethane are the two main components of natural gas and typically constitute more than 95% of it. In this study, a mixture of 90% CH4 /10% C2H6 diluted in 99% Ar was studied at fuel lean (ϕ = 0.5) conditions, for pressures around 1, 4, and 10 atm. Using laser absorption diagnostics, the time histories of CO and H2O were recorded between 1400 and 1800 K. Water is a final product from hydrocarbon combustion, and following its formation is a good marker of the completion of the combustion process. Carbon monoxide is an intermediate combustion species, a good marker of incomplete/inefficient combustion, as well as a regulated pollutant for the gas turbine industry. Measurements such as these species time histories are important for validating and assessing chemical kinetics models beyond just ignition delay times and laminar flame speeds. Time-history profiles for these two molecules measured herein were compared to a modern, state-of-the-art detailed kinetics mechanism as well as to the well-established GRI 3.0 mechanism. Results show that the H2O profile is accurately reproduced by both models. However, discrepancies are observed for the CO profiles. Under the conditions of this study, the measured CO profiles typically increase rapidly after an induction time, reach a maximum and then decrease. This maximum CO mole fraction is often largely over-predicted by the models, whereas the depletion rate of CO past this peak is often over-estimated by the models for pressures above 1 atm. This study demonstrates the need to improve on the accuracy of the HCCO reactions involved in CO formation for pressures of practical interest for the gas turbine industry.
Very Large Eddy Simulation (VLES) of a Squealer Tipped Axial Turbine Stage
Authors: Kelly Ryan , Jemcov Aleksandar , Cameron Joshua D. , Morris Scott C. , Coffman Jesse , Malak Malak F.
Published: August 2017

This work presents numerical simulation results of a single stage axial turbine consisting of a nozzle and squealer tipped rotor. The VLES method is a hybrid URANS/LES method based on the standard k-ω SST and Coherent Structure LES turbulence models. The simulations were performed at the stage aerodynamic design point (ADP) and the results were validated against high-quality steady experimental data acquired at the University of Notre Dame’s axial transonic research turbine (TRT) facility. Along with the experimental validation, the VLES simulation results were further compared to those predicted using URANS highlighting the benefits of VLES compared to traditional predictive methods. All simulations were performed using a RANS-type grid density to highlight the efficiency of the VLES method and improved performance prediction.
Investigation of Aerodynamics and Heat Transfer of a Highly Loaded Turbine Blade Using the Universal Intermittency Function
Authors: Nikparto A. , Schobeiri M. T.
Published: August 2017

Efficiency and performance of gas turbine engines are affected by the flow field around the blades. The flow field inside a gas turbine engine is very complex. One of the characteristics of the flow inside an engine is existence of periodic unsteady wakes, originating from the upstream stator blades. The unsteady wakes, with their highly vortical core, impinge on the downstream blade surfaces and cause an intermittent transition of the flow regime from laminar to turbulent. This study aims at investigating and modeling the behavior and development of the boundary layer along the suction surface of a highly loaded low-pressure turbine blade under steady and unsteady inlet flow condition. The current paper includes results of a computational work substantiated by the experimental verifications. For the experimental investigations, the linear cascade facility in Turbomachinery Performance and Flow research Lab (TPFL) at Texas A&M University was used to simulate the periodic unsteady flow condition inside gas turbine engine. Moving wakes, originating from upstream blades, were simulated in this facility by moving rods attached to two parallel timing belts. Measurements and calculations were conducted at Reynolds number of 110,000. This Reynolds number pertains to cruise condition of a low-pressure turbine. At this Reynolds number, the flow around the blades is transitional and highly susceptible to flow separation. Aerodynamics experiments include measuring the boundary layer, locating its transition, separation and finally re-attachment using miniature hot wire probes. Heat transfer measurements along the suction and pressure surfaces were conducted utilizing a specially designed heat transfer blade that was instrumented with liquid crystal coating. To numerically simulate the transitional behavior of the boundary layer under periodic unsteady flow condition, a new intermittency function is developed which is based on the universal intermittency function developed by Chakka and Schobeiri [1]. Accurate prediction of the boundary layer behavior under the above conditions requires minimum and the maximum intermittency functions. These functions were developed inductively using the experimental results that were obtained in the absence of flow separation. In the current investigation the impact of the separation on the minimum and maximum intermittency are accounted for. The enhanced minimum and maximum intermittency functions along with the universal intermittency are implemented in a RANS based solver for computational simulation. The computational results are compared with (a) experimental ones and (b) with the computational results from RANS that involves Langtry-Menter [2, 3] method.
Film Cooling Effectiveness Comparison on Full-Scale Turbine Vane Endwalls Using PSP Technique
Authors: Shiau Chao-Cheng , Chen Andrew F. , Han Je-Chin , Azad Salam , Lee Ching-Pang
Published: August 2017

Turbine vane endwalls are highly susceptible to intensive heat load due to their large exposed area and complex flow field especially for the first-stage of the vane. Therefore, a suitable film cooling design that properly distributes the given amount of coolant is critical to keep the vane endwall from failure at the same time to maintain a good balance between manufacturing cost, performance, and durability. This work is focused on film cooling effectiveness evaluation on full-scale heavy duty turbine vane endwall and the performance comparison with different film cooling pattern designs in the literature. The area of interest of this study is on the inner endwall (hub) of turbine vane. Tests were performed in a three-vane annular sector cascade under the mainstream Reynolds number 350,000; the related inlet Mach number is 0.09 and the freestream turbulence intensity is 12%. Two variables, coolant-to-mainstream mass flow ratios (MFR = 2%, 3%, 4%) and density ratios (DR = 1.0, 1.5) are investigated. The conduction-error free Pressure sensitive paint (PSP) technique is utilized to evaluate the local flow behavior as well as the film cooling performance. The presented results are expected to provide the gas turbine engine designer a direct comparison between two film-hole configurations on a full-scale vane endwall under the same amount of coolant usage.
Experimental and Modeling Study of C1 to C3 Hydrocarbon Ignition in the Presence of Nitric Oxide
Authors: Gokulakrishnan Ponnuthurai , Fuller Casey C. , Klassen Michael S.
Published: August 2017

Nitric oxide produced during combustion will be present in vitiated air used in many devices with exhaust gas recirculation. An experimental and modeling investigation of the effect of nitric oxide on the ignition of C1 to C3 hydrocarbon fuels, namely, CH4, C2H4, C2H6 and C3H6, is presented. These molecules are important intermediate species generated during the decomposition of long-chain hydrocarbon fuel components typically present in jet fuels. Moreover, CH4 and C2H6 are major components of natural gas fuels. Although the interaction between NOx and CH4 has been studied extensively, limited experimental work is reported on C2H4, C2H6 and C3H6. NOx, even in very low concentrations, has previously been shown to effectively enhance the ignition of CH4. As a continuation of previous work with C3H8, ignition delay time measurements were obtained using a flow reactor facility with the alkanes (CH4 and C2H6) and olefins (C2H4 and C3H6) at 900 K and 950 K temperatures with 15 mole% and 21 mole% O2. Based on the experimental data, the overall effectiveness of NO in promoting ignition is found to be: CH4 > C3H6 > C3H8 > C2H6 > C2H4.

CSE’s detailed kinetic mechanism, developed for natural gas fuel components, is used for model predictions as well as for sensitivity and species flux analyses. As expected, the reaction between HO2 and NO plays a critical role in promoting the ignition by generating the OH radical while converting NO into NO2. In addition, various important fuel-dependent reaction pathways that promote the ignition of these fuels are identified. H-atom abstraction by NO2 has significant contribution to the ignition of C2H4, and C2H6 whereas the reaction between NO2 and allyl radical (aC3H5) is an important route for the ignition of C3H6.
Active Control of Fuel Cell Degradation in an SOFC/GT Hybrid System
Authors: Zaccaria Valentina , Tucker David , Traverso Alberto , Pezzini Paolo , Bryden Kenneth M.
Published: August 2017

A control strategy to mitigate fuel cell degradation effects in a solid oxide fuel cell (SOFC) gas turbine (GT) hybrid system was implemented on the Hybrid Performance facility at the National Energy Technology Laboratory. In this experiment, a cyber-physical approach was employed to emulate the SOFC component and to couple it to a physical recuperated gas turbine. An empirical degradation model simulated fuel cell performance decay over time depending on operating parameters. A combination of virtual and physical actuators was manipulated with the goal of ensuring safe fuel cell performance over time, maintaining constant voltage and minimizing thermal stresses as fuel cell power degraded. Three single-input single-output controllers were used for this purpose. In particular, a gain scheduling approach was used for voltage control to account for different degraded conditions of operation because stability could not be maintained with the initial controller gains. In addition, a bypass valve control was designed to maintain constant temperature difference across the cell, and turbine load was manipulated to keep constant speed.

This work presents the control design and implementation on the Hybrid Performance facility and illustrates the impact of fuel cell degradation on the entire system long-term performance. Controllers design was based on empirical transfer functions and stability analysis. Issues related to coupling phenomena between controlled variables are discussed. The results show the potential for an adequate control of the system to extend fuel cell operating lifetime.
Vane Suction Surface Heat Transfer in Regions of Secondary Flows: The Influence of Turbulence Level, Reynolds Number and the Endwall Boundary Condition
Authors: Varty J. , Soma L. W. , Ames F. E. , Acharya S.
Published: August 2017

Secondary flows in vane passages sweep off the endwall and onto the suction surface at a location typically close to the throat. These endwall/vane junction flows often have an immediate impact on heat transfer in this region and also move any film cooling off the affected region of the vane. The present paper documents the impact of secondary flows on suction surface heat transfer acquired over a range of turbulence levels (0.7% through 17.4%) and a range of exit chord Reynolds numbers (500,000 through 2,000,000). Heat transfer data are acquired with both an unheated endwall boundary condition and a heated endwall boundary condition. The vane design includes an aft loaded suction surface and a large leading edge diameter. The unheated endwall boundary condition produces initially very high heat transfer levels due to the thin thermal boundary layer starting at the edge of heating. This unheated starting length effect quickly falls off with the thermal boundary layer growth as the secondary flow sweeps up onto the vane suction surface. The heat transfer visualization for the heated endwall condition shows no initial high heat transfer level near the edge of heating on the vane. The heat transfer level in the region affected by the secondary flows is largely uniform, except for a notable depression in the affected region. This heat transfer depression is believed due to an upwash region generated above the separation line of the passage vortex, likely in conjunction with the counter rotating suction leg of the horseshoe vortex. The extent and definition of the secondary flow affected region on the suction surface is clearly evident at lower Reynolds numbers and lower turbulence levels when the suction surface flow is largely laminar. The heat transfer in the plateau region has a magnitude similar to a turbulent boundary layer. However, the location and extent of this secondary flow affected region is less perceptible at higher turbulence levels where transitional or turbulent flow is present. Also, aggressive mixing at higher turbulence levels serves to smooth out discernable differences in the heat transfer due to the secondary flows.
Project-Based Learning Applied in Turbopump Discipline at ITA Using 1D and 3D Numerical Simulations of a Booster Turbine Installed in the Space Shuttle Main Engine
Authors: Whitacker Luiz Henrique Lindquist , Tomita Jesuino Takachi , Bringhenti Cleverson
Published: August 2017

Due to the critical importance of the turbopump applied in Liquid-Propellant Rocket Engines (LPRE) and the importance in the use of specific engineering software to design and analyze turbomachines, a Project-Based Learning (PBL) methodology was implemented in the undergraduate Turbopumps (TP) discipline at the Aeronautics Institute of Technology (ITA), taught for aerospace engineering students. This methodology was applied, using as a class example, the Liquid Oxygen (LOX) booster turbine of the Space Shuttle Main Engine (SSME), aiming at an enhancement in the discipline’s syllabus, to become the theory and practice closer to the real engineering, and to increase the discipline’s attractiveness. The results obtained with this methodology showed that the students have more interest and attention in the classes in which an engineering problem is evaluated and discussed with details using appropriate examples and engineering software that are used by the academia and industry. Several turbomachines issues as velocity triangles, power, blade geometrical aspects, flow quality, losses and in this case, the importance of tip clearance, could be better understood by the students. About the numerical results, the aim is that the students, after the preliminary project ends, evaluate the results and compare them with experimental data from National Aeronautics and Space Administration (NASA). One of the most important experience in this project is the results evaluation by the students and the discussion around it, as lessons learned, given suggestions to improve the project, if the results are not in the right way what can be done to correct them and understanding all physical phenomena involved. The learning experience was fascinating and effective, as noticed by students and noted by Professors.
Effect of Pressure and Thermal Cycling on Compatibility in CO2 for Concentrated Solar Power Applications
Authors: Pint Bruce A. , Brese Robert G. , Keiser James R.
Published: August 2017

A lifetime model is being developed for supercritical CO2 (sCO2) compatibility for the 30 year duty life for concentrated solar power (CSP) applications at >700°C to achieve higher efficiencies than other power cycles. Alloys 740H, 282, 625 and Fe-base alloy 25 are being evaluated in 500-h cycles at 1 bar and 300 bar, and 10-h cycles in 1 bar industrial grade CO2 at 700°–800°C. For comparison, companion experiments are being conducted in 1 bar air or O2. Using mass change, all of the alloys showed low mass gains with parabolic rate constants below the performance metric after 1000 h. However, alloy 25 showed a higher rate at 700°C in 300 bar sCO2 and did not follow an Arrhenius relationship. After 1500 h in 1 bar CO2, a much faster rate was observed for alloy 25 due to the formation of Fe2O3, but a similar increase was not observed in 300 bar CO2. Oxide thickness measurements have been completed after 1000 h in each condition. Only minor differences were noted between the 1 and 300 bar exposures. Up to 4,000 h exposures in 10-h cycles has not resulted in evidence of scale spallation but very small mass losses for alloy 625 were consistently observed. As longer exposures times are completed, quantification of the reaction products as a function time will be used to better model the degradation rate and additional characterization techniques will be included to further develop the model.
Assessment of UV Sensors for Flameout Detection
Authors: Bahous Edouard , Srinivasan Ram , Saxena Priyank , Bowen John
Published: August 2017

UV sensors were tested to evaluate the response and reliability as a flameout detection system to reduce system level risks. In this study, UV sensors from two manufacturers were tested on high pressure experimental rigs and on a 15MW gas turbine engine with annular diffusion flame combustion system. Tests were run to investigate the effect of fuel composition, engine load, and sensor circumferential position. The effect of each variable on sensor signal strength and response time is presented in this paper. The response time of the sensor is evaluated against the rate of change of combustor pressure and the time for fuel-air mixture to reach lean extinction limit in the primary zone. Results show that the UV sensor response is not affected by engine load, circumferential location of the sensors, or fuel composition down to Wobbe index of 18.7 MJ/Sm3. At lower Wobbe indices, the signal strength decreased significantly. This result has been attributed to the movement of flame location away from the line of sight of the sensor. Furthermore, it was found that the UV sensor responded before the bulk average reactant mixture reached lean blow out fuel-air ratios. When compared to the baseline detection system the UV sensor performs faster at low load conditions (800 milliseconds) but slower at full load conditions (400 milliseconds). Experimental rig testing led to similar conclusions for sensor response time and signal strength. Future testing of UV sensors on hydrogen blends is planned.
Steady State Analysis of Direct Thermal Energy Storage in Solid Oxide Fuel Cells (SOFC)
Authors: Moloney Francesca L. , Harun Nor Farida , Tucker David
Published: August 2017

This study explored the potential for TES in solid oxide fuel cells (SOFCs) by investigating the steady state fuel cell performance with a one-dimensional numerical model. The effect of including TES was simulated by increasing and decreasing the mass of the interconnect, stainless steel 441, as the storage medium. Using a model previously developed and tested in MATLAB Simulink®, the interconnect mass was varied from 42% to 99% of the total SOFC mass under the same initial and inlet conditions. The SOFC fuel studied was syngas derived from coal. As the size of the TES increased for constant cathode air mass flow, the heat capacity increased, resistance to heat conduction decreased and the temperature profile through the fuel cell became more uniform. As temperature gradients decreased, thermal stresses and the chance of cell failure reduced. Larger interconnect masses resulted in higher cell voltage and thus yielded higher efficiencies. The cathode air mass flow was also adjusted to control two different temperature conditions: constant average temperature and constant solid temperature difference across the cell. Instead of minimizing the size of the interconnect to reduce the cost of the SOFC, the interconnect material can be increased to add sensible heat storage directly to the fuel cell, increase heat and electrical conduction, and improve the efficiency of the fuel cell for hybrid systems as well as stand-alone fuel cells.
An Aeromechanical Screening Tool for Turbine Blades
Authors: Chakrabarti Suryarghya , Grafitti Andrew , Potter Brian
Published: August 2017

A design tool has been developed to calculate the natural frequencies of shrouded or unshrouded gas turbine blades in seconds to allow designers to perform aeromechanical frequency avoidance checks in the early concept design phase. The tool derives its inputs from a pitch-line aerodynamic calculation and a 1D structural design tool and uses a NACA-based airfoil section generator to create the airfoil sections. It then generates a shell-element based finite element model for the blade and disk sector, performs a pre-stressed modal analysis, and ranks the blades according to their frequency margins with specified aerodynamic drivers. Validation studies comparing this simplified model to high-fidelity solid element FEA models show the frequency error to be below 5% for most cases. The speed of this tool allows for frequency assessment of thousands of designs in a few hours allowing the designer to perform large spacefilling DoEs and select a flow path which minimizes the chances of fundamental mode crossings in later design stages..
Connecting Computed-Tomography-Assisted Discontinuity Detection in Ni-Base Superalloys to Engineering Simulation
Authors: Loghin Adrian , Cerrone Al , Singhal Anjali , Zhou Ying
Published: August 2017

The impact of non-metallic inclusions on fatigue life of various materials (steel alloys, Ni-base) has been studied extensively for more than fifty years. Specimen test procedures at various conditions (temperature, air or vacuum, LCF, HCF, VHCF) have been used to quantify the impact of inherent manufacturing induced discontinuities (ceramic inclusions, pores, carbides) on the fatigue capability of the material. Frequently, the fatigue data shows large scatter, leading to a large set of test specimens that has to be considered to quantify the lower tail of the fatigue life distribution. To understand the specimen recorded fatigue lives, assessment of the discontinuity population is usually conducted post-mortem by fractography wherein the origin of crack nucleation, size of the eventual inclusion on fracture surface, and distance from the free surface are identified.

3D characterization techniques can be leveraged to extract previously unobtainable information out of the testing specimens non-destructively. In this study, samples of different Powder Metallurgy (PM) Ni-base superalloys with different inclusion content and size were scanned to identify the Computed Tomography (CT) test setup that would provide adequate contrast to discriminate between matrix and eventual discontinuities (inclusions, pores). To further validate the capability to identify discontinuities within the matrix (Ni base alloy) using the CT technique, a set of LCF specimens were scanned prior to the test procedure. Post-failure fractography analysis showed that one of the CT indications is correlated with the failure-inducing inclusion.

Volume reconstruction and finite element meshing conclude this study to: a) further provide a size distribution of inclusions in the scanned volume as well as location of these inclusions relative to the surface of the specimen and b) connect direct measurement with engineering simulation.
An Experimental Investigation on the Impact of Inlet Slugging on Wet Gas Compressor Performance
Authors: Bakken Martin , Bjørge Tor
Published: August 2017

The continuous demand for oil and gas forces the petroleum industry to develop new and cost-efficient technologies in order to increase recovery and exploit existing fields. Subsea wet gas compression of the unprocessed well stream is a powerful tool in increasing production capacity and utilizing remote regions.

Wet gas compressors are particularly useful for handling gas-dominated multiphase flows. Although a limited amount of research has been done on the field, previous studies have revealed that the liquid phase has considerable impact on the compressor performance, from both a fluid mechanical and a thermodynamic perspective.

Being able to ensure stable and predictable compressor behavior in subsea installations is challenging. As the reservoir pressure drops during production, the compressor enters a region where it is far more susceptible to inlet slugging. Inlet slugging may lead to internal compressor damage, including damage to seals, bearings and compressor blades. It needs to be stressed that a slug in this context does not entail 100% liquid holdup upfront of the compressor, but a substantial increase of liquid content in a gas dominated multiphase flow.

An experimental investigation has been carried out on an advanced wet gas test rig, consisting of a shrouded centrifugal impeller, a vaneless diffuser and a circular volute. The paper explores the possibilities of creating realistic inlet slugging scenarios and documents its impact on the compressor system. Slugging was introduced either by collection of liquid in a negatively sloped inlet pipe (i.e. terrain slug simulation) or by sudden opening of an inlet liquid valve upstream of a symmetrical injection manifold, so to create a more “homogenous” slug. The compressor ability to handle such slugs is analyzed. Furthermore, the drive capability to respond to sudden changes in torque requirement is documented. The experimental results form a basis for future dynamic simulation.