bluuebunny/crossref_metadata_2025 huggingface dataset:
Reducing Instrumentation Errors Caused by Circumferential Flow Field Variations in Multi-Stage Axial Compressors
Authors: Chilla M. , Pullan G. , Gallimore S.
Published: November 2019

The effects of blade row interactions on stator-mounted instrumentation in axial compressors are investigated using unsteady numerical calculations. The test compressor is an 8-stage machine representative of an aero-engine core compressor. For the unsteady calculations, a 180deg sector (half-annulus) model of the compressor is used.

It is shown that the time-mean flow field in the stator leading edge planes is circumferentially non-uniform. The circumferential variations in stagnation pressure and stagnation temperature respectively reach 4.2% and 1.1% of the local mean. Using spatial wave number analysis, the incoming wakes from the upstream stator rows are identified as the dominant source of the circumferential variations in the front and middle of the compressor, while towards the rear of the compressor, the upstream influence of the eight struts in the exit duct becomes dominant. Based on three circumferential probes, the sampling errors for stagnation pressure and stagnation temperature are calculated as a function of the probe locations. Optimization of the probe locations shows that the sampling error can be reduced by up to 77% by circumferentially redistributing the individual probes. The reductions in the sampling errors translate to reductions in the uncertainties of the overall compressor efficiency and inlet flow capacity by up to 50%.

Recognizing that data from large-scale unsteady calculations is rarely available in the instrumentation phase for a new test rig or engine, a method for approximating the circumferential variations with single harmonics is presented. The construction of the harmonics is based solely on the knowledge of the number of stators in each row and a small number of equi-spaced probes. It is shown how excursions in the sampling error are reduced by increasing the number of circumferential probes.
Optimization Design Analysis of Primary Surface Recuperator for Rotorcraft Powerplant Applications
Authors: Zhang Chengyu , Gümmer Volker
Published: November 2019

The growing demand for highly efficient, environmentally friendly aero-engines highlights the incorporation of recuperators into gas turbine systems, which is especially attractive for rotorcraft powerplants, as the majority of their mission time is spent at part load cruise power (typically above 60%) with the non-optimum specific fuel consumption (SFC) characteristic. In this work, a primary surface recuperator (PSR) for the 300kW-class rotorcraft powerplant is considered for optimization by using a Genetic Algorithm (GA). By the very nature of aero-engines application, two different objective optimizations are conducted, aimed at minimizing the recuperator weight or/and reducing pressure drop, maximizing recuperator effectiveness. The geometries of the surface plate remain constant, while three shape parameters work as variables for defined constraints. The optimization process proves that GA is an adequate tool in recuperator design optimization according to the specified objectives. Based on calculation results, potential recuperator designs for aero-engine application are suggested.
Combustion Instabilities of Separated Stratified Swirling Flames With Different Degrees of Premixedness
Authors: Wang Xinyao , Han Xiao , Hui Xin , Zhang Chi , Song Heng , Lin Yuzhen , Sung Chih-Jen
Published: November 2019

The effects of premixedness degrees on combustion instabilities of separated stratified swirling flames have been investigated experimentally in the Beihang Axial Swirler Independently-Stratified (BASIS) burner. The degree of premixedness is modulated by the fuel split between two injection positions in the outer stream. In the spectra of pressure oscillations, both the dominant frequency and amplitude of partially premixed flames are positively correlated with fuel split ratios. The partially premixed flame is found to feature a large-scale periodic convective motion based on CH* chemiluminescence images, which have been analyzed under different fuel split ratios by a point-to-point Fast Fourier Transform (FFT) method. The development of above convective motion is explained by combining the variation of pressure and heat release in the oscillation period. Local Rayleigh index maps show that the driving factor of combustion instability for the partially premixed flame mainly comes from the upstream of the combustor. Finally, thermoacoustic network analysis is applied to predict observed frequencies under both perfectly and partially premixed conditions. The supposed additional convective time due to equivalence ratio fluctuations and the elongated flame region for the partially premixed flame is validated by its longer time delay in the sensitivity analysis of the n-τ flame model.
Compression Technology Selection for Downhole Application in Gas Wells
Authors: Malkawi Ameen , AlAdawy Ahmed , Gadamsetty Rajesh Kumar V. , Lastra Melo Rafael
Published: November 2019

Downhole gas compression technology is an artificial lift method that aims to boost production, maximize recovery and delay onset of liquid loading in gas wells. There are different available compression technologies that can be considered for downhole applications, such as screw, scroll, centrifugal and axial compressors. Selection of the appropriate type mainly depends on expected well performance, ambient conditions, compressor operating envelope, technology characteristics, limitations and size constraints. The objective of this study is to perform a feasibility evaluation of compression solutions applicable for a given set of candidate gas wells.

Aerodynamic and hydraulic models are used to determine operating conditions, compressor performance, and to select equipment specifications such as impeller diameter, compressor envelope, shaft HP requirement and number of stages among other parameters. A Pugh analysis is performed for all compression technologies and their characteristics to down-select the most suitable solutions for the given set of wells.

The results of the analysis indicated an optimal downhole compression technology that covers most of the gas flow rate requirements and meet the performance expectations. The study also provided critical specifications for the compressor, including high-speed operation needed to provide the required flow rates and compression ratio for a relatively small housing diameter. The study also finds that other technologies may be applicable but only to certain population of wells, as the flow rate spectrum is narrower than the optimal solution at the studied conditions. The analysis for the discarded compression technologies in this study showed relatively significant disadvantages for downhole application when compared to the selected compressor.

This study presents a holistic analysis for compression technology selection for gas wells that, as per to the understanding of the authors, is unique in the existing literature of gas well applications.
Flow-Driven Design Optimization of Centrifugal Compressor Volutes for Turbochargers
Authors: Tanganelli Andrea , Andreini Giulia , Rossini Matteo , Balduzzi Francesco , Bianchini Alessandro , Ferrara Giovanni
Published: November 2019

The design of the volute (in terms of area distribution and shape of the cross section) has a relevant impact on the efficiency and the operating range of a centrifugal compressor. This latter aspect is even more relevant in turbochargers, where the compressor has to cover a functioning range much wider than that of industrial applications. In addition, beyond conventional aerodynamic requirements, the design of the cross section shape is driven often in these applications also by space constraints imposed by the vehicle layout, leading to a variety of volute layouts. In a previous study, some of the authors highlighted the prospects of using the entropy generation rate to evaluate the losses within a volute, since this parameter allows an exact localization of irreversibilities. Starting from these results, the present study shows the suitability of this parameter as an indicator for the fine design optimization of the volute shape. A methodology is presented, which, based on the CFD computed contours of both the entropy generation rate and the total pressure, is able to drive the fine optimization of the volute cross-section at different azimuthal positions in order to maximize its efficiency. Multiple volute shapes are analysed in the paper and the effect of the operating conditions is accounted for by investigating different mass flow rates. The proposed approach indeed lead to a maximization of the volute efficiency with only a few trials and it could indeed provide room for future automatized fine optimization strategies.
Validation of a Numerical Quasi One-Dimensional Model for Wave Rotor Turbines With Curved Channels
Authors: Tüchler Stefan , Copeland Colin D.
Published: November 2019

A wave rotor is a shock-driven pressure exchange device that, whilst relatively rarely studied or indeed, employed, offers significant potential efficiency gains in a variety of applications including refrigeration and gas turbine topping cycles. This paper introduces a quasi one-dimensional wave action model implemented in MATLAB for the computation of the unsteady flow field and performance characteristics of wave rotors of straight or cambered channel profiles. The purpose here is to introduce and validate a rapid but reliable method of modelling the performance of a power-generating wave rotor where little such insight exists in open literature. The model numerically solves the laminar one-dimensional Navier-Stokes equations using a two-step Richtmyer TVD scheme with minmod flux limiter. Additional source terms account for viscous losses, wall heat transfer, flow leakage between rotor and stator endplates as well as torque generation through momentum change.

Model validation was conducted in two steps. First of all, unsteady and steady predictive capabilities were tested on three-port pressure divider rotors from open literature. The results show that both steady port flow conditions as well as the wave action within the rotor can be predicted with good agreement. Further validation was done on an in-house developed and experimentally tested four-port, three-cycle, throughflow micro wave rotor turbine featuring symmetrically cambered passage walls aimed at delivering approximately 500 W of shaft power. The numerical results depict trends for pressure ratio, shaft power and outlet temperature reasonably well. However, the results also highlight the need to accurately measure leakage gaps when the machine is running in thermal equilibrium.
The Impact of Model Assumptions on the CFD Assisted Design of Gas Turbine Packages
Authors: Lucherini Gabriele , Michelassi Vittorio , Minotti Stefano
Published: November 2019

A gas turbine is usually installed inside a package to reduce the acoustics emissions and protect against adverse environmental conditions. An enclosure ventilation system is keeps temperatures under acceptable limits and dilutes any potentially explosive accumulation of gas due to unexpected leakages. The functional and structural integrity as well as certification needs of the instrumentation and auxiliary systems in the package require that temperatures do not exceed a given threshold. Moreover, accidental fuel gas leakages inside the package must be studied in detail for safety purposes as required by ISO21789. CFD is routinely used in BHGE (Baker Hughes, a GE Company) to assist in the design and verification of the complete enclosure and ventilation system. This may require multiple CFD runs of very complex domains and flow fields in several operating conditions, with a large computational effort. Modeling assumptions and simulation set-up in terms of turbulence and thermal models, and the steady or unsteady nature of the simulations must be carefully assessed. In order to find a good compromise between accuracy and computational effort the present work focuses on the analysis of three different approaches, RANS, URANS and Hybrid-LES. The different computational approaches are first applied to an isothermal scaled-down model for validation purposes where it was possible to determine the impact of the large-scale flow unsteadiness and compare with measurements. Then, the analysis proceeds to a full-scale real aero-derivative gas turbine package. in which the aero and thermal field were investigated by a set of URANS and Hybrid-LES that includes the heat released by the engine. The different approaches are compared by analyzing flow and temperature fields. Finally, an accidental gas leak and the subsequent gas diffusion and/or accumulation inside the package are studied and compared. The outcome of this work highlights how the most suitable approach to be followed for industrial purposes depends on the goal of the CFD study and on the specific scenario, such as NPI Program or RQS Project.
Impact of the Reaction Mechanism Model on Soot Growth and Oxidation in Laminar and Turbulent Flames
Authors: Tardelli Livia , Franzelli Benedetta , Rodrigues Pedro , Darabiha Nasser
Published: November 2019

Numerical prediction of soot production in turbulent flames is extremely challenging, as it involves complex physical and chemical processes whose modeling presents today many uncertainties. The modeling of soot growth and oxidation reactions is a key aspect for soot prediction accuracy, as it may greatly contribute to the soot mass yield as numerically observed by Rodrigues et al. [1] in a turbulent non-premixed ethylene-airflame. Surface reactions are commonly described by a HACA-based model that is known to provide good agreement with experimental data in laminar premixed flames, while failing the description of laminar diffusion flames. A modification of the HACA-RC model [2], which is an extended version of the original HACA mechanism [3], is proposed here based on the work of Hwang et al. [4] in order to obtain a soot model that performs reasonably well on both premixed and diffusion laminar flames. To assess its accurary validations are performed on different laminar flames by comparison with available experimental data. Then, the impact of such modification on the prediction of turbulent flames is evaluated by performing two Large Eddy Simulations (LES) of a model gas turbine combustor using the new model and the reference HACA-RC model. The obtained results are compared to the experimental data in terms of soot volume fraction. Discrepancies between the two LES results are finally explained by analyzing the different source terms of soot production.
Measurement Drift in 3-Hole Yaw Pressure Probes From 5 Micron Sand Fouling at 1050° C
Authors: Turner Edward J. , Bogdan Matthew F. , O’Connell Tyler M. , Ng Wing F. , Lowe Kevin T. , Crook Loren , Stevenson Richard , Roberts James
Published: November 2019

The present paper focuses on the resilience of 3-hole pressure probes to hot sand fouling in turbomachinery environments. These probes are utilized inside jet engine hot sections for diagnostics and flow characterization. Ingestion of sand and other particulates pose a significant risk to hot section components and measurement devices in gas turbine engines. In this study, wedge, cylindrical, and trapezoidal probes were exposed to hot section turbine aerothermal conditions of 1050°C and 65–70 m/s flow velocity and fouled with 0–5 μm Arizona Road Dust (ARD). Sand accumulated more rapidly on the surface of the trapezoidal and cylindrical probe geometries than on the surface of the wedge probe geometry.

Probe calibrations following sand fouling were performed in an ambient temperature, open air, calibration jet at Mach 0.3 and 0.5. Calibration curves using non-dimensional coefficients were used to assess probe error in yaw angle due to sand fouling. Probe error was based on each probe’s ability to accurately measure flow direction over a flow angle range of [−10°, 10°]. On average, the probes displayed greater error at Mach 0.5 than Mach 0.3. The wedge probe performed the best after sand fouling and displayed a maximum error of less than ±2° in yaw angle. In contrast, the cylindrical probe performed the worst after sand fouling and displayed maximum errors of more than ±8° in yaw angle. Transient response did not change notably with sand fouling.
Disappearing Thermo-Economic Sanity in Gas Turbine Combined Cycle Ratings: A Critique
Authors: Gülen S. Can
Published: November 2019

There is very little doubt that there has been a noticeable advance in heavy-duty industrial gas turbine technology for utility scale electric power generation in the last decade. In keeping with the first six decades of the technology (roughly 1950 through 2010), the main drivers in increasing thermal efficiency and megawatt ratings have been increasing turbine inlet temperature and airflow. In accordance with the basic thermodynamic principles governing the underlying Brayton cycle, compressor pressure ratio kept pace with them.

It is hard to quibble about the 40+ percent in rated thermal efficiency in simple cycle. If projected turbine inlet temperatures and cycle pressure ratios can be sustained in the field, current state-of-the-art in turbine hot gas path metallurgy, coatings and advanced film cooling techniques indeed support published ratings. Unfortunately, published combined cycle ratings are an altogether different matter. It is one thing to set the product line rating performance at an aggressive level with well-understood albeit optimistic assumptions such as very low water-cooled steam turbine condenser pressure with open-loop cooling. It is yet another thing to blatantly disregard fundamental laws of thermodynamics with outlandish performance ratings, which are unlikely to materialize even in the next decade or two cost-effectively (unless an unforeseen transformative step-change in technology materializes). In this paper, using fundamental thermodynamic arguments and detailed heat and mass balance simulations, it will be shown that some, if not all, OEM ratings are losing touch with reality.
An Experimental and Numerical Investigation of the Aerodynamic Characteristics of a Flameless Combustor
Authors: Huijts M. P. , A. V. Perpignan A. , G. Rao A.
Published: November 2019

The flameless combustion (FC) regime is a promising technology for gas turbines, as it potentially yields lower NOx emissions while maintaining high combustion efficiencies. However, the application of FC to gas turbines is still challenging as required conditions for its occurrence depend on several factors such as reactants mixing, residence times, heat losses, and chemical time-scales. Since the mixing of the reactants and incoming fresh air-fuel mixture plays an important role in FC, the aerodynamic characteristics of the combustor are instrumental in determining the combustor emission performance. Focusing on the aerodynamic characteristics, this paper is dedicated to the visualization and description of the flow inside a jet-based combustor designed to operate under FC. The cylindrical combustor has a FLOX® burner head with 12 concentrically placed nozzles, while an acrylic cylinder allowed full optical access to the flow field. The investigation was performed for non-reactive flow. Using Particle Image Velocimetry and a Reynolds-averaged Navier-Stokes CFD analysis, the flow was visualized and modelled. The simulations were run with the Standard and Realizable k-ε (SKE and RKE, respectively), as well as a Reynolds Stress turbulence model. The effect of modifying the SKE model C1ε constant was also investigated. In the experimental campaign, the influence of combustion chamber length, nozzle diameter, and jet velocity were investigated with respect to flow structure, recirculation ratios and entrainment behavior.

The results show that the flow structure is mainly dependent on nozzle diameters, while the jet momentum is the correct parameter to assess the recirculation impact of a certain jet flow. The numerical investigation shows that the turbulence intensity at the boundaries is an important parameter to accurately simulate the jet spreading. None of the used turbulence models fully represented the flow field. Nonetheless, the SKE model with model C1ε = 1.44 was the best at representing the jets penetration and vortex core positions, and the recirculation ratio values predicted by it were in good agreement.
Corner Stall Prediction in a Compressor Linear Cascade Using Very Large Eddy Simulation (VLES) Lattice-Boltzmann Method
Authors: Maros Antoine , Bonnal Benoît , Gonzalez-Martino Ignacio , Kopriva James , Polidoro Francesco
Published: November 2019

Compressor corner stall is a phenomenon difficult to predict with numerical tools but essential to the design of axial compressors. Predictive methods are beneficial early in the design process to understand design and off-design limitations. Prior numerical work using Navier-Stokes computational methods have assessed the prediction capability for corner stall. Reynolds Averaged Navier-Stokes (RANS) simulations using several turbulence models [1] have shown to over-predict the region of corner hub stall where Large Eddy Simulations (LES) and Detached Eddy Simulations (DES) approaches improved the airfoil surface and wake pressure loss prediction [2, 3].

A linear compressor cascade designed and tested at Ecole Centrale de Lyon [3,4] provides a good benchmark for the evaluation of the accuracy of numerical methods for corner stall. This paper presents results obtained with Lattice-Boltzmann Method (LBM) coupled with Very Large-Eddy Simulations (VLES) approach of PowerFLOW and compares them with the experimental and numerical work from Ecole Centrale de Lyon. The ability to achieve equivalent accuracy at a lower computational cost compared to LES scale resolving methods can enable multi-stage design and off-design compressor predictions.

A methodical approach is taken by first accurately simulating the upstream flow conditions. Geometric trips are modeled upstream on the endwalls to match both the mean and fluctuating inflow boundary layer conditions. These conditions were then applied to the simulation of the linear compressor cascade. The benchline experimental study includes trips on both the pressure and suction of the airfoil. These trips are also included for the current simulation. The significance of capturing both inflow conditions and including trips on the airfoil are assessed. Detailed comparisons are then made to airfoil loading and downstream losses between experiment and previous RANS and LES simulations. LBM-VLES corner stall results of pitchwise averaged total pressure match LES agreement relative to experimental data at 50 times lower computational cost.
Phase-Opposition Control of the Precessing Vortex Core in Turbulent Swirl Flames for Investigation of Mixing and Flame Stability
Authors: Lückoff Finn , Sieber Moritz , Paschereit Christian Oliver , Oberleithner Kilian
Published: November 2019

The precessing vortex core is a helically-shaped coherent flow structure that occurs in reacting and non-reacting swirling flows undergoing vortex breakdown. In swirl-stabilized combustors, this flow structure affects important phenomena, such as turbulent mixing and thermoacoustic oscillations. In this work, a flow control system is developed to achieve appropriate conditions to systematically investigate the influence of the PVC on turbulent flames. The control consists of a zero-net-mass-flux actuator placed in the mixing section of the combustor, where the PVC is most receptive to periodic forcing. The actuator is driven in a closed loop to achieve phase-opposition control of the PVC. The flow control system is characterized from pressure measurements and particle image velocimetry and the impact on flame dynamics is extracted from OH*-chemiluminescence measurements. The data reveal that the PVC amplitude is considerably suppressed by the phase-opposition control without changing the overall characteristics of flow and flame. This is a very important requirement to study the exclusive effect of the PVC on combustion processes. Moreover, the control allows the PVC amplitude to be adjusted gradually to investigate the PVC impact on turbulent mixing and flame dynamics. It is revealed that the PVC-induced flow fluctuations mainly affect the large-scale mixing, while the small scale mixing remains unchanged. This is because the suppression of the PVC allows other modes to become more dominant and the overall turbulent kinetic energy budget remains unchanged. The destabilization of other modes, such as the axisymmetric mode, may have some implications on thermoacoustic instability.
Solar Desalination Based on Micro Gas Turbines Driven by Parabolic Dish Collectors
Authors: Sánchez David , Rollán Miguel , García-Rodríguez Lourdes , Martínez G. S.
Published: November 2019

This paper presents the preliminary design and techno-economic assessment of an innovative solar system for the simultaneous production of water and electricity at small scale, based on the combination of a solar micro gas turbine and a bottoming desalination unit. The proposed layout is such that the former system converts solar energy into electricity and rejects heat that can be used to drive a thermal desalination plant.

A design model is developed in order to select the main design parameters for two different desalination technologies, phase change and membrane desalination, in order to better exploit the available electricity and waste heat from the turbine. In addition to the usual design parameters of the mGT, the impact of the size of the collector is also assessed and, for the desalination technologies, a tailored multi-effect distillation unit is analysed through the selection of the corresponding design parameters. A reverse osmosis desalination system is also designed in parallel, based on commercial software currently used by the water industry.

The results show that the electricity produced by the solar micro gas turbine can be used to drive a Reverse Osmosis system effectively whereas the exhaust gases could drive a distillation unit. This would decrease the stack temperature of the plant, increasing the overall energy efficiency of the system. Nevertheless, the better thermodynamic performance of this fully integrated system does not translate into a more economical production of water. Indeed, the cost of water turns out lower when coupling the solar microturbine and Reverse Osmosis units only (between 3 and 3.5 €/m3), whilst making further use the available waste heat in a Multi Effect Distillation system rises the cost of water by 15%.
Transient Loading on Turbomachinery Packages due to Pressure Waves Caused by Accidental Deflagration Events
Authors: Gauch Hannes L. , Bisio Valentina , Rossin Stefano , Montomoli Francesco , Tagarielli Vito L.
Published: November 2019

In this study we present the application of numerical and analytical models to predict the transient loading of structures by impinging pressure and shock waves in air, which have been recently developed by the authors. Non-dimensional design maps are provided which yield predictions of the maximum loads on structures as a function of the problem parameters. Practical example applications, with reference to typical structures used in turbomachinery packages, are presented. These examples demonstrate the superiority of the new modelling techniques to current industrial design guidelines which are mostly extrapolated from simplified methods developed for shock waves. Finally, conclusions are drawn regarding the nature of the loading exerted on the structure in different regimes of problem parameters.
Evaluation of the Optimum Hybrid Power to Heat Configuration for a Gas Turbine Based Industrial Combined Heat and Power Plant
Authors: Klein Sikke , van Deursen Femke
Published: November 2019

Combined heat and power (CHP) is a very efficient way to generate both power and heat. However due to the increase in renewable power, the position of CHP in the energy system shifts: 1) the benefits of low effective CO2 emissions and low primary fuel consumption decrease and 2) the income from the generated power will show stronger fluctuations and will generally decrease.

Most CHP plants have shifted from base load operation to flexible operation on the power market to cope with these challenges. But due to the requirement for stable heat supply, flexible operation is more challenging than for a CCGT plant.

Significant flexibilization of CHP plants can be achieved by the integration with power to heat (P2H): the heat supply requirement enables the opportunity to create value out of low electricity prices during periods of excess renewable power generation using hybrid CHP-P2H-operation while during hours with high electricity prices and relatively low renewable power generation the CHP plant can run economically in its original configuration.

In this paper a study is executed on the implementation of P2H in an industrial CHP plant for four different configurations, varying from a ‘simple’ external electrical boiler to a full integration using air preheating and flue gas heating. The added flexibility and reduction of fuel consumption of these configurations have been calculated.

The economic analysis identified the imbalance market as the most attractive option for a hybrid CHP-P2H installation. The maximum income is generated by the CHP-P2H configuration that combines an inlet air preheater with electrical duct firing.

P2H appears to be a technical feasible option to make existing CHP installations fit for operation on a power market with an increasing share of renewable power.
Impact of Flame Lifting on Nitrogen Oxide Emissions From Premixed Reacting Jets in a Vitiated Crossflow
Authors: Sirignano M. D. , Nair V. , Sunkara D. , Emerson B. L. , Seitzman J. , Lieuwen T. C.
Published: November 2019

This paper describes measurements of nitrogen oxide (NOx) emissions from reacting jets in crossflow (RJICF). Primary factors that influence RJICF NOx emissions are: jet stoichiometry, mixing between jet and crossflow before combustion, and mixing of the remainder of the crossflow with the combustion products of the secondary combustion region. The aforementioned mixing is controlled by shear layer vortices and the counter-rotating vortex pair, as well as flame lifting. The coupled effects of bulk averaged temperature rise as a result of the RJICF (ΔT), jet stoichiometry (ϕJet), and momentum flux ratio (J) present a challenge in understanding critical factors controlling NOx production as it is difficult to vary them independently. Therefore, significant attention was paid to designing a test matrix that differentiated these effects. The data reported herein were obtained from the injection of premixed ethane/air or ethane/methane/air mixtures into a vitiated crossflow at one of two temperatures (1350K and 1410K). Varying the ethane/methane ratio allowed for systematic variation of flame lifting independent of ϕjet and J. The jets contained sufficient fuel to create an adiabatic bulk temperature rises from 75K–350K, with J values from 8–40, and ϕJet values from 0.8–8.0. The reported measurements confirm that NOx emissions increase monotonically with ΔT, as discussed in literature, but also indicates that the lifting of the flame significantly impacts NOx production. Lifting itself is a function of the variables described above and was quantified with chemiluminescence imaging. In fact, flame lifting is the dominant factor influencing NOx emissions, including ΔT.
Effect of Surface Roughness Induced by Laser Powder Bed Fusion Additive Manufacturing in a Mini-Channel Heat Exchanger
Authors: Parent-Simard T. , Landry-Blais A. , Dubois P. K. , Picard M. , Brailovski V.
Published: November 2019

The Inside-Out Ceramic Turbine (ICT) is a promising microturbine for aeronautics applications. To increase the cycle efficiency and reduce fuel consumption, microturbines must operate under the recuperated Brayton cycle. The addition of a heat exchanger (HEx) increases the weight of the engine and cancels out any fuel savings as compared to a non-recuperated turbine. For this reason, the requirements applied to HEx for aeronautic gas turbines are: low weight and volume, high effectiveness with a low pressure drop, capabilities to endure high pressure and temperature, and low cost. The Laser powder bed fusion (LPBF) opens a new design space for geometries that cannot be realized by conventional methods, but induces high surface roughness. This paper presents experimental and analytical studies of the influence of surface roughness on the performances of a 3D-printed, counterflow, mini-channel HEx, with 1% of the total mass flow rate of the ICT. Results showed that the friction and heat transfer are both increased in the the regime typically defined as laminar compared to the analytical results. The experimental results are in agreement with a 1D heat transfer model when using correlations for high-roughness values from the literature. LPBF is a promising method to manufacture gas turbine parts, but it is crucial to model and incorporate its manufacturing capacities in terms of precision and surface finish to enhance HEx heat transfer and potentially reduce mass.
Untwist Creep Analysis of Gas Turbine First Stage Blade
Authors: Jarrett Anthony , Erukulla Veda V. , Koul Ashok K.
Published: November 2019

During operation, turbine blades subjected to high temperatures will experience permanent geometric distortion due to creep. The principal form of this distortion is blade elongation due to the centrifugal load, but the blade can also straighten or ‘untwist’. The magnitude of the untwist can be used to track the accumulated creep strain damage in a blade, and so measurements of blade untwist over time are often recorded. If the relationship between untwist and creep strain damage can be expressed, then it will be possible to make more informed maintenance decisions.

This study describes a finite element creep analysis of a first stage turbine blade using a calibrated creep material model, and compares the calculated untwist to records kept by the operator.

The creep model used in this study is a physics based model using the microstructural properties of the blade alloy, and is calibrated using a single creep test at representative stress and temperature. An important objective of this study is to demonstrate that application of the creep model in a component with non-uniform stress and temperature will lead to representative results.

The analysis was repeated with two materials that correspond to different blade versions. The material with superior high temperature properties exhibited less untwist, and the analysis of both variants were comparable to the recorded blade measurements.
Impact of Dust Feed on Capture Efficiency and Deposition Patterns in a Double-Walled Liner
Authors: Cory Trevor M. , Thole Karen A. , Kirsch Kathryn L. , Lundgreen Ryan , Prenter Robin , Kramer Stephen
Published: November 2019

The introduction of particulates into gas turbine engines poses a serious threat to component durability. Particles drawn from the environment, such as ash or sand, can be introduced into the air system used to cool hot section components and drastically diminish cooling performance. In the current study, a dirt-laden coolant stream impinged on a double-walled cooling configuration, which was comprised of an impingement plate followed by an effusion-cooled plate. Experiments were conducted at both room temperature and at temperatures in excess of 750°C; flow conditions were varied to achieve different pressure ratios across the cooling configuration. Dirt particles were introduced into the coolant using two different methods: in discrete bursts, called slugs; or in a continuous feed ensuring a constant stream of particles. This continuous feed mechanism is at the crux of a new test facility created to introduce flexibility and precision in the control of dirt feed rates, particularly for very small (< 50 mg) amounts of dirt.

The difference in capture efficiency and in dirt patterns between the two feed methods showed measurably different dirt accumulation levels on the cold side of the effusion plate at the same test conditions. Results show that the slug feed method caused higher capture efficiency and thicker dirt deposition on the effusion plate compared to the continuous feed.
CMC Mode II Crack Growth Resistance Prediction of ASTM Specimen and Test Validation
Authors: Abdi Frank , Godines Cody , Presby Michael J. , Eftekharian Amir , Ahmad Jalees , Choi Sung , Morscher Gregory N. , Gonczy Steve , Shi Jun
Published: November 2019

The objective of this effort is to predict ceramic matrix composites (CMC) interlaminar Mode II Crack Growth Resistance (CGR), and the design of ASTM test specimen. Currently, there are a number of test standards and American Society for Testing and Materials (ASTM) for CMC’s at both ambient and elevated temperatures; however, there are no standardized test methods for determination of interlaminar shear (Mode II) fracture toughness in CMC’s. Although research work exists on interlaminar Mode II fracture toughness of CMC’s, the test methods applied showed definite drawbacks and limitations. Delamination Crack Growth (CGR) tests of CMC Mode II may exhibit zig-zag pattern, wavy cracks, fiber bridging, and premature specimen failure under bending load. The experimental parameters that may contribute to the difficulty can be summarized as specimen width and thickness, interface coating thickness, mixed mode failure evolution, and interlaminar defects. Modes II crack growth resistances, GII, were analytically and numerically determined at ambient temperature using end notched flexure (ENF) and the end-loaded split (ELS). Finite Element (FE) based. Multi-scale progressive failure analysis (MS-PFA) a combined Micro-mechanical damage and fracture mechanics Virtual Crack Closure Technique (VCCT) algorithms. Modeling of melt-infiltrated SiC/SiC CMC of ENF specimen (Laminate: with initial crack length was accomplished using a MS-PFA and VCCT approach. Test data were compared with MS-PFA prediction: a) Force vs. Crack Opening Displacement; and b) Mode II crack tip energy release rate vs. crack extension length for both edge and center line due to formation of Micro Crack Density Contribution, Crack Tip Stiffness Reduction; and c) zig-zag crack growth behavior (adhesive/cohesive). Next the ASTM Standard Proposed linear SGR equation was developed based on interpretation compliance technique from both MS-PFA Analysis and Test.
Influence of Blade Flexibility on the Dynamic Response Simulation of a Turbomolecular Pump on Magnetic Bearings
Authors: Barbosa Moreira Alysson Bruno , Thouverez Fabrice
Published: November 2019

This paper proposes the simulation of a complete mechanical model of a turbomolecular pump rotor, including rotor and blades flexibility, suspended by controlled active magnetic bearings. The mechanical model is composed of an eight stage blisk, attached to a shaft. Magnetic forces are linearized by first order Taylor expansion around a given point. Including blades and rotor flexibility makes the mechanical system asymmetric, so the equations of motion for the coupled system have periodic terms. A modal controller was designed to control rigid body modes, since the number of sensors is limited and no state observer is implemented. PID controllers are used for low frequency modes combined with second order filters to damp high frequency modes. First of all, stability analysis was carried out for the axisymmetric case. Secondly, blades flexibility was included. Forced response of the whole system to an impulsive force was studied. Divergent responses for the system in rotation were obtained as a second order filter pole possibly interacts with blades modes. Taking second order filters off the control loop allowed the system to be stable. These results show that the analysis method developed here is efficient to evaluate the performance of a controller in closed loop with the complete flexible system. This method may be used in industrial design processes as computation times for the complete system are very short.
Dynamic Characterization and Identification of Flow in a Blade Passage in Near-Stall Conditions of Axial Compressor Systems
Authors: Aung Eighdi , Schoen Marco P. , Li Jichao
Published: November 2019

Axial compressor systems are susceptible to unstable conditions near their optimal operating point. In particular, rotating stall and surge are conditions that need to be avoided during the operation of an axial compressor. In extreme cases these conditions may cause damage to the compressor. The onset of either condition is rather rapid, and usually does not allow for remedial control action based on the limited time available. Hence, research efforts have been focusing on the development of new detection methods that allow for more time to take corrective measures. This paper explores and compares various existing and proposed methods to identify and detect those precursors. The methods detailed in this work are tested at different operating conditions and locations. The methods investigated include the sequentially computed correlation coefficient of pressure sensor data, correlation coefficient, the Generalized Extreme Studentized Deviate Test (ESD) for outlier detection, spectral entropy, and Autoregressive (AR) models. The primary goal of evaluating these methods is based on their suitability for employment as pre-processors for dynamic system identification. By using the dynamics of the identified model rather than a static precursor, it is stipulated that the onset of stall and surge can be managed with a control concept. For this work, the extracted models are investigated for suitability to serve as precursors, and the potential as predictive models. This work may serve for future work to achieve active flow control by direct air injection at the leading edge of the blades. For this work, a one-stage compressor system with a blade geometry that allows for spike inception is utilized. Spike stall inception is a precursor to fully developed rotating stall. The subsonic compressor has 60 blades, and its operating point is controlled by a throttle and constant speed control of the rotor. The pressure data is collected with 10 Kulite™ sensors which are placed along the blade cord length on the outer casing of the compressor. The results of the tabulated performance of the various methods and resulting models indicate that an ARESD combination yields the earliest indication for spike stall inception.
The Effect of Rotor-Stator Gap on Repeating-Stage Compressor Loss
Authors: Przytarski Pawel J. , Wheeler Andrew P. S.
Published: November 2019

In this paper we study the effect of rotor-stator axial gap on midspan compressor loss using high fidelity Large-Eddy Simulations. For this purpose we mimic the multi-stage environment using a new numerical method which recycles wake unsteadiness from a single blade passage back into the inlet of the computational domain. As a result a type of repeating-stage simulation is obtained such as observed by an embedded blade-row. We find that freestream turbulence levels rise significantly as the size of the rotor-stator axial gap is reduced. This is because of the effect of axial gap on turbulence production, which becomes amplified at smaller axial gaps and drives increases in dissipation and loss. This effect is found to raise loss by between 7–9.5% over the range of conditions tested here. This effect significantly outweighs the beneficial effects of wake recovery on loss.
Effect of High Pressures on the Formation of Nitric Oxide in Lean, Premixed Flames
Authors: Versailles Philippe , Durocher Antoine , Bourque Gilles , Bergthorson Jeffrey M.
Published: November 2019

Increasingly stringent regulations are imposed on nitrogen oxides emissions due to their numerous negative impacts on human health and the environment. Accurate, experimentally validated thermochemical models are required for the development of the next generation of combustors. This paper presents a series of experiments performed in lean, premixed, laminar, jet-wall stagnation flames at pressures of 2, 4, 8, and 16 atm. To target post-flame temperatures relevant to gas turbine engines, the stoichiometry of the non-preheated methane-air mixture is adjusted to an equivalence ratio of 0.7. One-dimensional profiles of temperature and NO mole fraction are measured via laser-induced fluorescence (LIF) thermometry and NO-LIF, respectively, to complement previously published flame speed data [1]. The results reveal that, as the pressure increases, the maximum post-flame temperature stays relatively stable, and the concentration of NO produced through the flame front remains constant within uncertainty. Seven thermochemical models, selected for their widespread usage or recent date of publication, are validated against the experimental data. While all mechanisms accurately predict the post-flame temperature, thanks to consistent thermodynamic parameters, important disagreements are observed in the NO concentration profiles, which highlights the need to carefully select the models used as design tools. The lack of pressure dependence of NO formation that many models fail to capture is numerically investigated via sensitivity and reaction path analyses applied to the solution of flame simulations. The termolecular reaction H+O2 (+M) ↔ HO2 (+M) is shown to hinder the production of atomic oxygen and hydrogen radicals at higher pressures, which inhibits the formation of nitric oxide through the N2O pathway.