bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study on Flutter Stability of Transonic Cooled Turbine Blade Stage With 3-Dimensional Mode Shape Excitation
Authors: Kang Jeongseek , Perez Ethan , Vorobiev Alex , Morris Scott , Cameron Joshua , Kim Daehyun , Im Hongsik , Montgomery Matthew
Published: January 2021

It is well known that mode shape plays very important role in stability of turbine blade since the aerodynamic work per cycle and aerodynamic damping depend on mode shape. With the advancements of theoretical formulation with influence coefficient method, experimental studies with rigid body blade motion have significantly improved understanding of turbine flutter mechanisms and design parameters. However rigid body motion cannot accurately match the complex mode shapes of modern turbine blade, so there are limitations of accuracy on experimental evaluation of flutter stability with rigid body blade motion.

This study utilized 3-dimensional mode shapes for evaluating aerodynamic work per cycle and stability of turbine blade through experimental method. A transonic annulus turbine cascade rig was built at Notre Dame Turbomachinery Laboratory. Three center blades with modern cooled 3-dimensional aero design were instrumented with 144 EA of ultraminiature fast-response pressure transducers on the blade surface at 50%, 75%, and 95% of blade spans. Center blade and adjacent blades were designed to have the same blade mode shape as a reference turbine blade and the center blade was actuated with an electromagnetic shaker at natural frequencies of 1st bending and 1st torsional modes to simulate the same level of reduced frequencies under engine operating condition. Mode shape scanning of test blade through laser doppler vibrometer confirmed the design intent of blade bending and torsional mode shapes and their frequencies. All the dynamic pressure measurements on the three center blades were synchronized with blade position measurement and influence coefficient method was applied to calculate aerodynamic work per cycle and damping parameter. It was found that pressure side generally stabilizes the blade and that there was strong stable zone from leading edge to about 20% in arcwise coordinate torward suction side. After this zone, a destabilizing zone follows and this can be strong enough to destabilize the blade in some range of nodal diameter.
Proof of Concept for a Novel Interstage Injection Design in Axial Compressors
Authors: Doerr T. , Braun S. , Schuster S. , Brillert D.
Published: January 2021

A common technique to increase the thermal efficiency and the power output of gas turbines is to inject water upstream of the compressor section. Through the evaporation of the water throughout the compressor, an isothermal process is approached. A recently-developed technology for this enhanced process is Interstage Injection in which water is injected directly between the stages. One advantage of this over wet compression is the avoidance of icing, since the local temperatures at the injection positions are already above melting point. Moreover, stage characteristics and load distribution can be rearranged within the compressor by individually adjusting the injection amount in different stages. However, there is little practical understanding of this process, and suitable injection methods have still to be found.

This paper therefore demonstrates the implementation of a novel technology of Interstage Injection in an axial compressor test rig whereby twin jet nozzles are integrated directly into the trailing edge of the first stator row to deliver a homogenous spray over the entire radial span. Due to the resultant blade complexity, blades are manufactured by selective laser melting and subsequently installed in an enhanced four-stage axial compressor. The installed control and measurement principles of the test rig are presented and results demonstrate the functionality of the innovative design.
Mass Spring Interlocked Bladed Disk Model
Authors: Córdoba Oscar
Published: January 2021

A simplified bladed disk model with cantilever and interlock conditions is described. Blade is composed of three masses, two for the lower and higher part of the shroud, and one for the main core of the blade. A similar scheme is employed in the disk. The different masses in the model are linked with springs introducing the stiffness between them. Additional disk restrictions reduce the model capabilities but account the effect of common boundary conditions. The model simplicity allows an analytical solution with polynomials to understand the fundamentals of vibration. The extended stiffness and mass matrix with Lagrange multipliers are used. The modal frequencies and modes as function of the nodal diameter are studied. The interlock solution is compared to cantilever and different sorts of frequency curves have been identified and classified. Some basic conclusions related to the model parameters are achieved.
Aero-Thermal Aspects of Film Cooled Nozzle Guide Vane Endwalls: Part 1 — Aerodynamics
Authors: Alqefl Mahmood H. , Nawathe Kedar P. , Chen Pingting , Zhu Rui , Kim Yong W. , Simon Terrence W.
Published: January 2021

The first stage turbine of a modern gas turbine is subjected to high thermal loads which lead to a need for aggressive cooling schemes to protect its components from melting. Endwalls are particularly challenging to cool due to the complex system of secondary flows near them that wash the protective film coolants into the mainstream. This paper shows that without including combustor cooling, the complex secondary flow physics are not representative of modern engines. Aggressive injection of all cooling flows upstream of the passage is expected to interact and change passage aerodynamics and, subsequently, mixing and transport of coolants. This study describes, experimentally, the aero-thermal interaction of cooling flows near the endwall of a first stage nozzle guide vane passage. The test section involves an engine-representative combustor-turbine interface geometry, combustor coolant flow and endwall film cooling flow injected upstream of a linear cascade. The approach flow conditions represent flow exiting a cooled, low-NOx combustor. This first part of this two-part study aims to understand the complex aerodynamics near the endwall through detailed measurements of passage three-dimensional velocity fields with and without endwall film cooling. The aerodynamic measurements reveal a dominant vortex in the passage, named here as the Impingement Vortex, that opposes the passage vortex formed at the airfoil leading edge plane. This Impingement Vortex completely changes our description of flow over a modern film cooled endwall.
Numerical Investigation of the Effect of Flutter Instability of the Blade on the Unsteady Flow in a Modern Low-Pressure Turbine
Authors: Naung Shine Win , Rahmati Mohammad , Farokhi Hamed
Published: January 2021

Modern aeronautical Low-Pressure Turbines (LPTs) are prone to aeroelastic instability problems such as flutter. The aerodynamic performance of a modern LPT is often influenced by the interaction between the transient flow and the dynamic behaviour of the blade. Therefore, the investigation and understanding of the physics behind the interaction between the unsteady flow and the flutter phenomenon of the blade in an LPT, which is normally left out by existing studies, is an important aspect of the research to improve the aerodynamic performance of the turbine as well as to ensure the blade mechanical integrity. In this paper, a novel analysis is conducted to explore the flutter instability in a modern LPT, T106A turbine, using two inter blade phase angles (IBPAs), and their effects on the unsteady flow field are investigated. The zero degree and 180 degrees IBPAs are considered in this paper. A high-fidelity direct numerical simulation method is used for the flow simulations. Another distinctive feature of this paper is the use of the 3D model to analyse the effects associated with the 3D blade structure and the 3D vibration mode. The investigation and identification of adequate working ranges of the harmonic balance method, which has been widely used for the aeromechanical analysis of turbomachines, are also presented in this work. This paper will bridge a key gap in the knowledge of aeroelasticity modelling and analysis of modern LPTs.
On Predicting Weld Specimen Fatigue Life Based on Defect Data
Authors: Roychowdhury Sushovan , Månsson Tomas
Published: January 2021

Prediction of fatigue life based on internal defect data is an important research topic for components built through both traditional welds and modern additive manufacturing. In this work, a systematic approach is taken to investigate application of fracture mechanics principle for this purpose. To this end, fatigue test samples are prepared from TIG-welded titanium alloy sheets and also representative weld repairs of cast plates. Metro-tomography is employed to obtain information about internal defects in the specimens before fatigue testing. After fatigue testing, fractography is used to identify the defect that led to failure and to gather information on its location and size. The information from metro-tomography and fractography are then directly compared to assess the accuracy of the tomography data. Simple fracture mechanics methods are employed to estimate the fatigue life for each specimen, considering separately tomography and fractography data. Such estimates are then compared with fatigue life from tests. Through such quantitative comparisons, the work highlights the advantages and the challenges of the fracture mechanics approach to assess the fatigue life of test specimens with internal defects. A key observation is that life estimates employing a fracture mechanics approach are reasonable when the defect leading to failure is known, but the challenge may lie in a-priori identification of the defect that would eventually lead to failure.
Quick Start of an Industrial Gas Turbine Engine Through the Development of “Silent Start” VGV Schedule
Authors: Krishnababu Senthil , Panov Vili , Jackson Simon , Dawson Andrew
Published: January 2021

In this paper, research that was carried out to optimise an initial variable guide vane schedule of a high-pressure ratio, multistage axial compressor is reported. The research was carried out on an extensively instrumented scaled compressor rig. The compressor rig tests carried out employing the initial schedule identified regions in the low speed area of the compressor map that developed rotating stall. Rotating stall regions that caused undesirable non-synchronous vibration of rotor blades were identified. The variable guide vane schedule optimisation carried out balancing the aerodynamic, aero-mechanical and blade dynamic characteristics gave the ‘Silent Start’ variable guide vane schedule, that prevented the development of rotating stall in the start regime and removed the non-synchronous vibration. Aerodynamic performance and aero-mechanical characteristics of the compressor when operated with the initial schedule and the optimised ‘Silent Start’ schedule are compared. The compressor with the ‘Silent Start’ variable guide vane schedule when used on a twin shaft engine reduced the start time to minimum load by a factor of four and significantly improved the operability of the engine compared to when the initial schedule was used.
The Effect of Wall Thermal Boundary Condition on Natural Convective Shutdown Cooling in a Gas Turbine
Authors: Fahy Daniel D. , Ireland Peter
Published: January 2021

As a civil gas turbine cools down, asymmetric natural convective heat transfer causes the bottom sector of the rotor to cool faster than the top; this circumferential thermal gradient can potentially cause the shaft to deflect — a phenomenon called thermal or rotor bow. Rotor bow is tremendously difficult to predict due to its dependence on a number of engine design parameters, in addition to the complex nature of natural convective flows.

A novel experimental facility has been developed to gain further understanding into shutdown cooling of a gas turbine. The scope of this paper is to quantify the effect of basic design features on natural convective cooling in an engine annulus during shut-down; specifically the influence of the thermal boundary wall conditions and the annular diameter ratio. In addition to this, a low-cost, robust thermocouple probe has been developed and validated, which allows for accurate temperature measurements in a natural convective boundary layer.

An extensive experimental campaign has been completed. The key finding is that the local radial wall temperature difference was found to be the most influential parameter on the local heat transfer. Non-isothermal walls did not alter the overall distribution of the inner wall equivalent conductivity. This was true for both cylindrical and conical sections. An appropriate characteristic length for use in the Rayleigh number definition for both the concentric cylinder and conical sections have been validated. The conical inner section (5° hade angle) did not affect the overall heat transfer in the range of conditions tested. Therefore, the mean surface heat transfer for non-isothermal inner and outer profiles, within the range −0.4 < ΔRa/RaLc < 0.4, where the thermal gradient is negative in the clockwise from top-dead-centre, can be predicted using isothermal correlations for RaLc < 5.0 × 105 and Dr <= 1.5.
Analysis of Nonlinear Modal Damping due to Friction at Blade Roots in Mistuned Bladed Discs
Authors: Chen Junjie , Zang Chaoping , Zhou Biao , Petrov E. P.
Published: January 2021

A method is proposed to analyse the modal damping in mistuned bladed-disc with root joints using large finite element models and the detailed description of frictional interactions at contact interfaces. The influence of mistuning on the dissipated energy for different blades on a bladed-disc and the modal damping factors for different vibration levels for any family of modes can be investigated.

The dissipated energy and damping factors due to micro-slip are simulated by multitude of surface-to-surface elements modelling the friction contact interactions at root joints. The analysis is performed in the time domain and an original reduction method is developed to obtain the results with acceptable computational times. The model reduction method allows the calculation of the modal damping of the mistuned assembly by evaluation of the energy dissipated at root joint of each individual blade using small parts of bladed disc sectors.

The dependency of modal damping factor on blade mode shapes, engine-order excitation numbers, nodal diameter numbers and vibration amplitudes are studied and the distributions of amplitude and dissipated energy on the mistuned bladed-disc are investigated using a realistic blade disc model.
Cooled Pressure Probes Design Methodology for Harsh Environment Applications
Authors: Clinckemaillie Julien , Fontaneto Fabrizio
Published: January 2021

The present paper discusses in detail the methodology adopted for the cooling layout design of a water-cooled fast-response wall-static pressure probe intended for measurements in the combustion chamber of gas turbines. The proposed design approach is structured upon three main steps. In the first step, different reduced order correlations for convective and radiative heat transfer are used to derive the heat load at which the measurement device is submitted. In the second part, a quasi-2D conjugate heat transfer model is developed and operated through the application of the boundary conditions computed in the previous step. The model is based on empirical correlations and computes representative global cooling performance parameters for different cooling layouts and coolant mass flow rates. In the final step, the obtained design candidate is further validated by means of state-of-the-art fully 3D conjugate heat transfer numerical simulations performed on a probe geometry characterized by an increased degree of complexity. At its final extent, the present paper describes and validates a complete and robust methodology for the design of a cooling layout for cooled fast-response pressure probes.
Comparison of Tabulated and Complex Chemistry Turbulent-Chemistry Interaction Models With High Fidelity Large Eddy Simulations on Hydrogen Flames
Authors: Zghal M. , Sun X. , Gauthier P. Q. , Sethi V.
Published: January 2021

Hydrogen micromix combustion is a promising concept to reduce the environmental impact of both aero and land-based gas turbines by delivering carbon-free and ultra-low-NOx combustion without the risk of autoignition or flashback. The EU H2020 ENABLEH2 project aims to demonstrate the feasibility of such a switch to hydrogen for civil aviation, within which the micromix combustion, as a key enabling technology, will be matured to TRL3. The micromix combustor comprises thousands of small diffusion flames where air and fuel are mixed in a crossflow pattern. This technology is based on the idea of minimizing the scale of mixing to maximize mixing intensity. The high-reactivity and wide flammability limits of hydrogen in a micromix combustor can produce short and low-temperature small diffusion flames in lean overall equivalence ratios.

In order to mature the hydrogen micromix combustion technology, high quality numerical simulations of the resulting short, thin and highly dynamic hydrogen flames, as well as predictions of combustion species, are essential. In fact, one of the biggest challenges for current CFD has been to accurately model this combustion phenomenon. The Flamelet Generated Manifold (FGM) model is a combustion model that has been used in the past decades for its predicting capabilities and its low computational cost due to its reliance on pre-tabulated combustion chemistry, instead of directly integrating detailed chemistry mechanisms. However, this trade for a lower computational cost may have an impact on the solution, especially when considering a fuel such as Hydrogen. Therefore, it is necessary to compare the FGM model to another combustion modelling approach which uses more detailed complex chemistry.

The main focus of this paper then, is to compare the flame characteristics in terms of position, thickness, length, temperature and emissions obtained from LES simulations done with the FGM model, to the results obtained with more complex chemistry models, for hydrogen micromix flames. This will be done using STAR-CCM+ to determine the most suitable numerical approach required for the design of injection systems for ultra-low NOx.
Development of a Multi-Phase Flamelet Generated Manifold for Spray Combustion Simulations
Authors: Zhang Xu , Yi Ran , Chen C. P.
Published: January 2021

In this study, a model flame of quasi-1D counterflow spray flame has been developed. The two-dimensional multiphase convection-diffusion-reaction (CDR) equations have been simplified to one dimension using similarity reduction under the Eulerian framework. This model flame is able to directly account for non-adiabatic heat loss as well as multiple combustion regimes present in realistic spray combustion processes. A spray flamelet library was generated based on the model flame. To retrieve data from the spray flamelet library, the enthalpy was used as an additional controlling variable to represent the interphase heat transfer, while the mixing and chemical reaction processes were mapped to the mixture fraction and the progress variable. The spray-flamelet/progress-variable (SFPV) approach was validated against the results from the direct integration of finite-rate chemistry as a benchmark. The SFPV approach gave a better performance in terms of temperature predictions, while the conventional gas-phase flamelet/progress-variable (FPV) approach over-predicted by nearly 20%. In terms of species mass fractions, there was no significant difference between the two, both showing good agreements with the direct integration of chemistry (DIC) model.
Aerodynamic and Structural Numerical Investigation of Full Annulus Last Stage of Steam Turbine Under Low Load Conditions
Authors: Qi Di , Chen Yifeng , Lin Gang , Li Wenfu , Tan Wei
Published: January 2021

Operating at low load conditions may cause strong and non-synchronous unsteadiness and a high blade dynamic loading for the last stage blades (LSB). Full annulus models should be used to investigate the circumferential asymmetric flow unsteadiness and blade vibrations. Currently, although full annulus models have been applied to numerical aerodynamic studies, to authors’ knowledge, there is still no research including the full annulus in structural analysis due to the high computational cost. In this paper, an unsteady aerodynamic and structural coupled analysis method for an industrial steam turbine LSB using full annulus model under low load conditions is presented. To conduct finite element method (FEM) with limited computational resources, a new structural analysis procedure is proposed to calculate the dynamic stress.

The aerodynamic analysis is conducted in both steady and unsteady computational fluid dynamics (CFD) calculations. The tip pressure ratio in the steady state calculations is used to predict the aerodynamic loading intensity. The unsteady results indicate typical flow characteristics under low load conditions, which show a big separation region behind the last rotor and tip vortex between last stator and rotor. Unsteady aerodynamic loading is mapped onto the blade surface as the excitation force. The structural analysis is performed to investigate the characteristics of blade vibrations and stress distributions of the full annulus LSB. Repeating the method, a reasonable characteristics curve of vibration stress against flow rates for LSB is calculated.
Development of a Constitutive Backstress Model for the Prediction of Creep and Stress Relaxation in Gas Turbine Materials
Authors: Moffat Andrew , Green Richard , Ferguson Calum , Scaletta Brent
Published: January 2021

There is a drive towards a broader range of fuels in industrial gas turbines, with higher levels of sulphur and potentially hydrogen. Due to these harsher environments, there is also a drive for corrosion resistant alloys and coatings. A number of key corrosion resistant superalloys, which are being employed to cope with these evolving conditions, exhibit primary creep. It is therefore imperative that fundamental material models, such as those for creep deformation, are developed to ensure they can accurately predict the material response to evolving operating conditions. The requirements for a creep model are complex. The model must be able to: predict forward creep deformation in regions dominated by primary loads (such as pressure); predict stress relaxation in regions dominated by secondary loads (such as differential thermal expansion); predict the effects of different creep hardening mechanisms. It is also clear that there is an interaction between fatigue and creep. With flexible operation, this interaction can be significant and should be catered for in lifing methods. A model that has the potential to account for the effect of plasticity on creep, and creep on plasticity is therefore desirable.

In previous work the authors presented the concept for a backstress model to predict creep strain rates in superalloys. This model was fitted to a limited dataset at a single temperature. The approach was validated using simple creep-dwell tests at the same temperature. This paper expands on the previous work in several ways:

1) The creep model has been fitted over a wide range of temperatures. Including the effect of temperature in complex creep models presents a number of difficulties in model fitting and these are explored.

2) The model was fitted to constant load (forward creep) and constant strain (stress relaxation) tests since any creep model should be able to predict both forms of creep deformation. However, these are often considered separately due to the difficulty of fitting models to two different datasets.

3) The creep deformation model was validated on stress change tests to ensure the creep deformation response can cope with changes in response variables.

4) The approach was validated using creep-fatigue tests to show that the creep deformation model, in addition to our established fatigue models, can predict damage in materials under complex loading.
Novel Desulfurization Concept Using a Regenerable Adsorbent
Authors: Vierling Matthieu , Geiger Frederic , Brilhac Jean-Francois , Dorge Sophie , Habermacher David , Nouali Habiba , Guichard Jean-Louis , Marchal Eric , Patarin Joel , Soulard Michel , Moliere Michel
Published: January 2021

Sulfur oxides, abbreviated to SOx, refer to both sulfur dioxide (SO2) and sulfur trioxide (SO3) that are gaseous pollutants emitted by the combustion of low-grade fuels, including heavy oils, sour gases and coal.

Current Flue Gas Desulfurization (FGD) technologies mainly use limestone or CaO (quicklime) as sulfur scavenger. They consume water and produce significant stocks of calcium sulfate, a non-regenerable solid that has limited market outlets and is sometimes considered as waste.

To tackle this problem, a multi-partner team has launched a two-phase program in order to develop a new, regenerative FGD concept. This partnership includes a GE Power team (Belfort, France), three research laboratories (IS2M-MPC, LGRE from University of Haute Alsace, Mulhouse and ICB-UTBM-LERMPS, Belfort), a ceramic material testing center (ICAR, Moncel les Luneville, France) and a consultancy organization skilled in materials (Zephir Alsace, Mulhouse). The main objective was to design a regenerable adsorbent that would not release any solid waste but would allow instead the recovery of sulfur in the form of H2SO4 (sulfuric acid) which is a valuable chemical commodity.

A first subprogram, executed from September 2012 through March 2015 and called “DeSOx New Gen”, enabled the different partners to identify and test at lab scale a regenerable and durable adsorbent. This adsorbent, used initially in powder form, involved an organized mesoporous silica (SiO2), which was used as a support and was impregnated with copper oxide (CuO) likely to undergo reversible sulfation. Such binary system proved capable of achieving large numbers of successive adsorption/regeneration cycles (more than fifteen attained in the lab) without undergoing substantial activity loss.

A second subprogram, initiated in September 2017 and called “AdSOx”, aimed to obtain and test a bead-shaped form of the previously developed adsorbent in view of industrial applications. This product in bead-shaped adsorbent was then evaluated in 2019 in a pilot combustion rig, the flue gases of which were representative of a real industrial combustion installation in terms of SOx, NOx, CO, CO2, H2O and PM (particulate matter). In these rig tests, the performances of the adsorbent for the capture of SOx, including its capability to be regenerated for multi-cyclic use, have been assessed in fluidized bed and most recently in fixed bed conditions.

This paper outlines the most significant steps and outcomes of this collaborative two-phase development program. It also illustrates the interesting capabilities of mesoporous materials for the design of highly active sorption and catalytic systems.
On-Line Component Map Adaptive Procedure Based on Sensor Data
Authors: Yang Xuesen , Guo Xiaofeng , Dong Wei
Published: January 2021

A key challenge in the gas turbine community is to adapt the engine model by matching measured data with simulation data. This study presents a procedure aiming to calibrate a certain type of gas turbine for power generation. To reproduce degradation, disturbance is injected into the healthy components maps at different time. Subsequently, six correction factors along with measured data and unmeasured parameters are coupled together using cooperative working equations and optimized based on primal-dual interior point method. When performing the adaptive procedure, Jacobian and hessian matrices are calculated using finite difference since the component maps have external, mapped, functions implemented as lookup-tables, and mode-switching statements. To improve the accuracy of first-order and second-order partial derivatives, the finite difference is enhanced by Richardson extrapolation method. The search scope of correction factors and unmeasured parameters are determined by the whole working conditions. Meanwhile, an adaptive update method of initial solution is proposed to make sure the convergence of the optimization procedure as quickly as possible. Finally, the proposed method is further applied to the on-line adaptation in case of performance degradation. The influence of measurement noise on optimization is also studied. It is demonstrated that the procedure is capable of refining the component maps progressively, which is significant for the model-based gas path diagnostics and prognostics.
Optimal Control of a Compound Rotorcraft for Engine Performance Enhancement
Authors: Scullion Calum , Vouros Stavros , Goulos Ioannis , Nalianda Devaiah , Pachidis Vassilios
Published: January 2021

Demands for rotorcraft with increased flight speed, improved operational performance and reduced environmental impact have led to a drive in research and development of alternative concepts. Compound rotorcraft overcome the flight speed limitations of conventional helicopters with additional lifting and propulsive components. Further to operational benefits, these augmentations provide additional flight control parameters, resulting in control redundancy. This work aims to investigate the impact of optimal control strategies for a generic coaxial compound rotorcraft, equipped with turboshaft engines, targeting the minimization of mission fuel burn and gaseous emissions. The direct redundant controls considered are: (a) main rotor speed, (b) propeller speed, and (c), fuselage pitch attitude. A simulation tool for coaxial compound rotorcraft analysis has been developed and coupled to a zero-dimensional engine performance model and a stirred-reactor combustor model. Firstly, experimental and flight test data were used to provide extensive validation of the developed models. A parametric analysis was then carried out to gain insight into the effect of the redundant controls. This was followed by the derivation of a generalized set of optimal redundant control allocations using a surrogate-assisted genetic algorithm. Application of the optimal redundant control allocations during realistic operational scenarios has demonstrated reductions in fuel burn and NOx of up to 6.93% and 8.74% respectively. The developed method constitutes a rigorous approach to guide the design of control systems for future advanced rotorcraft.
Numerical Modeling of Gaseous Partially Premixed Low-Swirl Lifted Flame at Elevated Pressure
Authors: Langone Leonardo , Sedlmaier Julia , Nassini Pier Carlo , Mazzei Lorenzo , Harth Stefan , Andreini Antonio
Published: January 2021

Lifted flames have been investigated in the past years for their benefits in terms of NOx emissions reduction for gas turbine applications. In a lifted flame, the flame front stabilized on a position that is significantly detached from the nozzle exit, improving the premixing process before the reaction zone. The distance between the flame front and the nozzle exit is called lift-off height and it represents the main parameter that characterize this type of flame. In the present work, a partially premixed lifted flame employing air-methane mixture is investigated through numerical simulation. Indeed, even if lifted jet flames have been widely studied in the literature, there are only a few examples of lifted partially premixed flames. Nevertheless, this kind of flames assumes an important role considering the current gas turbine applications, since their benefits in terms of stability and low pollutant emissions. This study has been performed with LES calculations using a commercial software suite and the numerical results are compared with experimental data coming from a dedicated campaign held at Karlsruher Institute für Technologie (KIT) on a novel low-swirl injector nozzle. Quenching effects due to strain, curvature and heat loss have been introduced into the combustion model thanks to a correction of the source term in the progress variable equation within the FGM model. The comparison between numerical results and experimental data have been performed in terms of lift-off height and OH* chemiluminescence maps, showing the capability to properly predict the overall flow and to catch flame lift-off even if with an underpredicted height. This points out promising capability of the numerical model in the representation of lifted flames, allowing further investigations of the flame structure otherwise not available from experimental techniques.
Two Phase Flow CFD Modeling to Enhance Steam Turbines LP Stages Performance Predictability: Comparison With Data and Correlations
Authors: Maceli Nicola , Arcangeli Lorenzo , Arnone Andrea
Published: January 2021

The whole energy market, from production plants to end-users, is marked by a strong impulse towards a sustainable use of raw materials and resources, and a reduction of its carbon foot-print. Increasing the split of energy produced with renewables, improving the efficiency of the power plants and reducing the waste of energy appear to be mandatory steps to reach the goal of sustainability.

The steam turbines are present in the power generation market with different roles: they are used in fossil, combined cycles, geothermal and concentrated solar plants, but also in waste-to-energy and heat recovery applications. Therefore, they still play a primary role in the energy production market.

There are many chances for efficiency improvement in steam turbines, and from a rational point of view, it is important to consider that the LP section contributes to the overall power delivered by the turbine typically by around 40% in industrial power generation.

Therefore, the industry is more than ever interested in developing methodologies capable of providing a reliable estimate of the LP stages efficiency, while reducing development costs and time.

This paper presents the results obtained using a CFD commercial code with a set of user defined subroutines to model the effects of non-equilibrium steam evolution, droplets nucleation and growth. The numerical results have been compared to well-known test cases available in literature, to show the effects of different modeling hypotheses. The paper then focuses on a test case relevant to a cascade configuration, to show the code capability in terms of bladerow efficiency prediction. Finally, a comprehensive view of the obtained results is done through comparison with existing correlations.
Understanding Risks: Natural Gas Distribution Piping in the United States
Authors: Lyons Sara , Modarres Mohammad
Published: January 2021

Two hundred sixty-nine regulated pipeline system accidents caused fatalities and/or injuries in the United States between 2010 and 2018, resulting in 106 fatalities and 599 injuries requiring hospitalization. About 84% of these serious accidents occurred on gas distribution systems, which primarily transport natural gas. This study adapts probabilistic risk assessment (PRA) methods which are used predominantly in the space and nuclear industries to gas distribution systems in the U.S. Nationwide system and accident data are used to evaluate natural gas distribution system risks, estimate how many additional resources the public would be willing to dedicate to reduce or eliminate these risks, and determine which improvement areas warrant further evaluation. Recommendations regarding the overall PRA-based framework, as well as the scope, quality, and level of detail of the underlying data, are provided.
Reliability Performance Benchmarks for Low Vapor Pressure Liquids Pipelines
Authors: Bandstra Daryl , Dessein Thomas , Schwing Aaron , Andrew Jim , Moritz Jason
Published: January 2021

The pipeline industry is increasingly utilizing reliability methods as a basis for decision-making when managing the integrity of pipeline systems. In this paper we present a methodology for developing reliability benchmarks for onshore low vapour pressure (LVP) liquids transmission pipelines to enable an operator to evaluate the performance of their pipelines relative to their industry peers. The goals of this methodology are to use an approach that is calibrated to historical performance, that remains interpretable, that can readily be adjusted over time, and that reflects the increased sensitivity of High Consequence Areas (HCAs).

On this basis, the Top Quartile (Q1) and Average historical environmental performance of the top 20 largest liquid pipelines operators were identified as two primary benchmarks of interest. Top Quartile (Q1) environmental performance represents an industry leading benchmark performance while the Average historical environmental performance is representative of typical pipelines. This group of operators was selected on the basis that these major companies operate pipeline networks with comparable complexity, similar integrity challenges and a diverse range of operating environments (urban, rural, etc.). In addition, the length of their respective systems decreases the impact of small sample size issues. The dataset used for calculating the historical environmental performance of these operators was the 2010–2018 PHMSA Hazardous Liquids Incidents and Annual Mileage datasets.

The framework presented in this paper, allows specific reliability benchmarks to be calculated for a given pipeline dependent on the environmental consequences associated with failure of the line. Consequences are considered in order to be risk-consistent between pipelines with different outflow potentials and different land use surroundings (HCA vs. Non-HCA). The heightened sensitivity of HCA areas is considered by including an impact ratio in calculating the reliability benchmarks.

These benchmarks can be used to identify pipelines for additional scrutiny when the expected environmental performance does not meet benchmark levels and to flag areas for further evaluation. Quantifying the failure potential of pipeline segments gives operators insights into which maintenance actions will make the most effective use of the available resources to improve reliability. These benchmarks are calculated directly from historical data using a simple methodology and are easily recalibrated in the future as the performance of the pipeline industry continuously improves to meet increasing societal expectations.
Reliability-Based Assessment of Safe Excavation Pressure for Dented Pipelines
Authors: Okoloekwe Chike , Fowler Matthew , Virk Amandeep , Yoosef-Ghodsi Nader , Kainat Muntaseer
Published: January 2021

Dents in a pipe result in alteration of its structural response when subjected to internal pressure. Excavation activities further lead to change in load and boundary conditions of the pipe segment which may exacerbate the stress state within the dented region. Depending on the severity of a dent, excavation under full operating pressure may lead to failure, injuries or fatalities. Although uncommon, an incident has been reported on a gas pipeline where a mechanical damage failed during investigation leading to one death and one injury [10]. While current pipeline regulations require that operators must depressurize a line to ensure safe working conditions during repair activities, there are no detailed provisions available in the codes or standards on how an operator should determine such a safe excavation pressure (SEP). As a result, the safe excavation process of dents has received attention in the industry in recent years.

A detailed review of the recent research on dent SEP showed that the current recommendations are primarily dependent on one of two aspects: careful assessment of inline inspection (ILI) data, or a fitness for service (FFS) assessment of the dent feature leveraging numerical models. Enbridge Liquid Pipelines had previously demonstrated a feature specific assessment approach which incorporated both ILI data and finite element analysis (FEA) to determine the SEP. This assessment also accounted for uncertainties associated with material properties and ILI tool measurement. In the previous publication, the authors demonstrated a methodology for assessing the SEP of dents at a conceptual level from both deterministic and reliability-based standpoints. In this paper, a validation study has been performed to compare the results of fracture mechanics based FEA models against ten full scale burst tests available in literature. The study showed good agreement of the burst pressure of dent-crack defects predicted by FEA models with those observed in the full-scale tests. The assessment method is further streamlined by incorporating the API 579 [14] Failure Assessment Diagram (FAD) method on an uncracked FEA model as opposed to explicitly incorporating the crack geometry in the FEA model. The results of FEA in conjunction with FAD are compared with the full-scale tests to ensure accuracy and conservatism of burst pressure prediction. A reliability-based approach is then designed which accounts for the uncertainties associated with the analysis. A case study is presented where the reliability-based SEP assessment method has been implemented and feature specific SEP has been recommended to ensure target reliability during excavation.
Effects of Flow Response on the Failure Pressure of Pipelines
Authors: Leis Brian N.
Published: January 2021

The flow properties of line-pipe steels control the failure resistance of the pipe, and as such are key in successful pipeline design, and in understanding the factors controlling failures when they occur. As first-principals predictive models are challenged to quantify the flow response in typical line-pipe steels, engineers must rely on empirically developed properties to support numerical analysis for purposes of design and/or integrity management. Stress-based design logically relies on a limiting stress, whereas strain-based design used to address issues like ground movement relies on a limit strain. Post-yield these limits are coupled through the steel’s stress-strain curve and strain-hardening response. Because the burst-pressure of pipes has been shown to depend on the steel’s collapse stress as well as its strain-hardening exponent, n, engineers will need more that the yield stress, Y, or the tensile stress, T, to adequately characterize a pipeline’s resistance to failure.

This paper presents results for the mechanical properties of line-pipe steels developed up to the ultimate tensile stress, or beyond. These stress-strain curves reflect 1) Grades ranging from vintage A25 through recent X100 production. These results have been analyzed to quantify n, Y, and T. These results have further been trended to relate commonly available metrics like Y/T and n, and provide a rational basis for the choice of properties input to numerical analysis.

It is apparent from this work that current correlations between n and Y/T diverge from the trend for the lower-strength Grades. Further, these results show that within a Grade the value of n is a strong function of the ratio of the actual yield stress (AYS) normalized by SMYS, with this dependence indicative of differences in the chemistry and processing used to achieve the Grade. The effects of n and its dependence on the ratio AYS/SMYS are illustrated regarding the predicted response of line pipes subject to increasing pressure. These predictions have been validated by comparison with results for about 20 full-scale tests to illustrate the viability of this technology.
Improving Reliability of Carbon Steel Girth Welds in Sour Environment
Authors: Sidhar Harpreet , Verma Neerav , Kuo Chih-Hsiang , Belota Michael , Wasson Andrew J.
Published: January 2021

The oil and gas industry has seen unexpected failures of sour service carbon steel pipelines in the recent past. Below par performance of girth welds and line pipe material have been identified as the root causes of such failures. Although mechanized welding can achieve good consistency, the weld region is more heterogeneous as compared to base material, which can lead to inconsistencies and poor weld performance. Overall, the effects of welding parameters on performance of carbon steel pipeline girth welds for sour service are not well understood. Furthermore, industry is moving towards more challenging environments, such as production of hydrocarbons from ultra-deepwater, which further necessitates the need to improve welding practices for additional high criticality applications. Many of the critical parameters for sour service performance will also improve general weld performance for ultra-deepwater. So, there is a clear need to understand the effects of various welding parameters on weld properties and performance.

This effort aims at assessing the effects of key welding parameters on performance of girth welds to develop improved welding practice guidelines for sour service pipeline applications. In this study, several API X65 grade line pipe girth welds were made using commercially available welding consumables. The effects on weld root performance of preheat, wire consumable chemistry, hot pass tempering, single vs. dual torch, copper backing, root pass heat input, metal transfer mode, pipe fit-up (root gap, misalignment) were studied. Generally, carbon steel welds with hardness 250HV or below are considered acceptable for sour service. So, detailed microhardness mapping and microstructural characterization were conducted to evaluate the performance and reliability of welds. It was evident that the welding parameters studied have a significant impact on root performance. Preheat and pipe fit-up showed the most significant impact on weld root performance. Based on the results and understanding developed with this study, recommendations for industry are provided through this paper to improve reliability of pipeline girth welds in sour service application.
Quantifying Risk to Optimize Facility Integrity Management
Authors: Nemeth Alex , Li Lily , Nielsen Andrew , Vignal Geoff
Published: January 2021

Effective asset integrity management is supported through the understanding of the condition of the asset, and the quantification of the safety and uncertainty of its properties. Risk based and risk informed decision making can help operators prioritize inspections and repairs on mainline pipe, as well as within operator facilities. Setting operator system specific targets for reliability and risk can help operators better understand the condition of their system, and provide one means of determining whether integrity action or other risk treatment is required on a specific asset, either on the mainline pipe system or on a facility asset system.

While mainline pipe condition is better understood through the use of inline inspection technology and non-destructive examination in the field, facility piping and storage condition is more difficult to understand due to the complexity and number of segments of assets within an operator’s facility, as well as the unpiggable nature of the majority of facility piping.

To help resolve this issue, a risk quantification can be done for each segmented asset within a facility. A relative ranking of asset risks can help prioritize facility integrity activities and drive the planning and execution optimization. However, simply looking at a relative ranking of asset risks may not be enough to maximize risk reduction and achieve safety and reliability targets.

This paper looks to expand on the implementation of Risk Based Inspection (RBI) standard in API 581 and explore more broadly how facility asset risk results can be used in integrity planning and decision making. The paper also examines the application of using finance principals to better quantify risk and carry out a meaningful cost benefit analysis to optimize integrity programs.

Interpreting a quantified risk dollar amount is an industry challenge, and shedding light onto the value of applying reliability and risk models beyond the safety of an operator’s system can be extremely beneficial for operators to enhance cost efficiency. The quantification of risk helps support the optimization of spend and resource allocation to bring efficiencies into integrity management systems while maintaining focus on the right risk mitigation across an operator’s system.