bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calibration of CDM-Based Creep Constitutive Model Using Accelerated Creep Test (ACT) Data
Authors: Hossain Md Abir , Mach Robert , Pellicotte Jacob , Stewart Calvin M. 
Published: January 2021

Abstract
In conventional creep testing (CCT) a specimen is subject to constant load and temperature for a long-duration until creep rupture occurs. Conventional testing can be costly when considering the number of experiments needed to characterize the creep response of a material over a range of stress and temperature. To predict long-term creep-rupture properties, the time-temperature-stress superposition principle (TTSSP) approach has been employed where stress and/or temperature is applied at an elevated level; the result of which are extrapolated down to low stress and/or temperature conditions. These methods have been successful in predicting minimum-creep-strain-rate (MCSR) and stress-rupture (SR) but suffer from an inability to predict the creep deformation curve or account for changes in deformation mechanisms or aging that occurs at long-duration. An accelerated technique, termed the Stepped isostress method (SSM) allows the accelerated testing of materials to determine their creep deformation response. Unlike TTSSP tests, the SSM test employs a single specimen where the stress is periodically step increased until rupture. The SSM creep deformation curve is processed (time and strain shifted) to produce an accelerated creep deformation curve that represent the creep deformation curve at the initial stress level in SSM. A processing procedure for metals has yet to be developed.
The research objective of this study is to develop a processing procedure for SSM test data using a creep-damage constitutive model. Triplicate SSM tests were conducted on Ni-based superalloy Inconel 718 at 650°C with stress being periodically increased until rupture. Triplicate CCT tests were conducted at the initial stress level of the SSM tests. The Sine-hyperbolic (Sinh) creep-damage model was employed in this study. The Sinh creep-damage constitutive model is based on coupled creep strain rate and damage evolution equations; where both rates are dependent on the current state of damage. Calibration is two-step: analytical and numerical optimization. Each stepped creep deformation curve is tackled quasi-analytically to determine MCSR and SR related material constants and accumulated damage. The damage accumulated at the end of each step was then passed onto subsequent steps to calibrate the MCSR, rupture prediction, and damage evolution. Numerical optimization was applied to optimize model constants involved in the creep strain constitutive equations in order to generate best-fitted Sinh creep deformation curves. The Sinh model predictions were compared to the SSM and CCT data. The Sinh model satisfactorily predicts the SSM data and thus the calibrated material constants provides a good estimate of rupture found in the CCT data. Calibration using SSM data reduces the number of tests needed to calibrate a model; significantly reducing costs. A single SSM test replaces numerous creep tests at different stresses.
Effect of Sloped Trench Casing Treatment on Performance and Stability of Axial Compressors
Authors: Jiexuan Hou , Yangwei Liu 
Published: January 2021

Abstract
Numerical simulations are carried out to investigate the effect of the sloped trench casing treatment on the performance and stability of a compressor cascade, an isolated rotor, and a single compressor stage. The research objects alter from a simplified flow model to an actual compressor working environment. Firstly, a detailed study of how the sloped trench casing treatment effects the tip leakage flow structure, especially the tip leakage vortex of a compressor cascade, is presented. Results show that the strength of the tip leakage vortex is weakened as the sloped trench casing treatment transforms the structure of the tip leakage vortex. Then the simulation results of the isolated rotor and the single stage are studied. For both cases, the effect of the sloped trench casing treatment on the tip leakage flow is analogous to that of the cascade case. For the isolated rotor, the improvement on the performance is not obvious. While under the stage environment, different from the traditional casing treatment, both the performance and the stability of the compressor are advanced, by getting the tip leakage vortex under control and letting the downstream stator working under a better inflow condition.
Mid-Span Stall Inception in a Transonic Fan
Authors: Verschueren H. , Hall C. A. , Wilson M. J. 
Published: January 2021

Abstract
In this paper, steady and unsteady CFD have been used to investigate stall inception for a modern low pressure ratio transonic fan. The computational results are validated against measurement data from a high-speed test facility. CFD validation was approached as a blind test case. The results shows good agreement between the experiments and computations.
Stall is triggered by growth of a suction surface separation behind the shock around the mid-span of the rotor blade. As the fan is throttled the separation grows leading to increased blockage in the blade passages. At the point of instability the separation grows further, locally increasing incidence and leading to the formation of a stall cell. It is shown that changes to the tip leakage flow leave the stall inception mechanism unaffected. A computational case with a suction surface slip patch between 25–75% span shows that the reduction in blockage around the mid-span increases the stall margin by 25%. This demonstrates that for cases with mid-span initiated stall it is important to consider the flow away from the tip as well as the flow in the tip region. A redesigned fan is used to illustrate that design changes around the mid-span can be effective to improve flow range. The redesigned fan increases stall margin by 6.7% while maintaining the design point efficiency within 0.1%.
Topology Optimization of a Turbomachinery Casing Structure Using the Level Set Method
Authors: Li Lei , Neofytou Andreas , Paiva Ricardo , Keskin Akin , Kim H. Alicia 
Published: January 2021

Abstract
A turbomachinery casing structure provides the necessary support to many crucial systems and components in an aeroengine such as the combustion chamber, compressors, and turbines. A competitive casing structure should be stiff and durable while minimizing weight. This work investigates the possibilities and potential of using topology optimization to design a turbomachinery casing structure to achieve certain design requirements. As the casing structure is in a high pressure system that undergoes complex mechanical loading conditions, the level set method is employed in contrast to the common density-based topology optimization methods, which could lead to physically uninterpretable gray elements for a complex loading environment. This paper describes the basic concept of the level set method and demonstrates the benefits in terms of boundary definition, speed, and applicability to engineering problems. Topology optimization with a linear-elastic analysis based on an axisymmetric finite element solver is employed in this study. Both minimum compliance and minimum stress problem formulations are considered, and a series of optimum designs are presented and discussed.
A Co-Simulation Approach to Modeling Air-Cooled Condensers in Windy Conditions
Authors: Engelbrecht Ruan , Laubscher Ryno , van der Spuy Johan 
Published: January 2021

Abstract
Air-cooled condensers (ACC) are commonly used for cooling applications in the petro-chemical and power generation industry. Common analysis techniques used include one-dimensional design codes, however, these fail to capture complex flow phenomena associated with ACCs subjected to adverse environmental conditions. Computational Fluid Dynamics (CFD) is seen as an alternative, more accurate analysis tool. The model used in the present study co-simulates the CFD using ANSYS Fluent® to model the air-side with a system-level model in Flownex® to represent the steam-side. A 4 × 3 ACC bank is subjected to adverse cross-wind conditions and a single cell is co-simulated. The volumetric and thermal performance is predicted. Prior to the evaluation a discretization process is undertaken to ascertain an adequate level of detail required to accurately capture the complex flow phenomena which could affect the steam-side performance. A 3 × 3 and 6 × 6 discretization case is compared. A 13% difference in heat transfer rate is predicted between the cases. The 6 × 6 case is used to evaluate the cell performance when the ACC is subjected to cross-wind speeds of 0, 3, 6 and 9 m/s. Results show an increase in outlet steam quality as the cross-wind speed increases due to diminishing ACC performance.
Exploring Topology Optimisation of High Pressure Turbine Blade Tips
Authors: Vincekovic Luka , John Alistair , Qin Ning , Shahpar Shahrokh 
Published: January 2021

Abstract
This work presents the aerodynamic topology optimisation of high pressure turbine rotor blade tips. Before carrying out the topology optimisation on the blade tip, some initial tip design studies were carried out. The winglet shape was optimised using two different design space setups and parameter limits. The optimum winglet design features the largest overhangs and in the case of unconstrained optimisation proved to have 1.40% greater aerodynamic efficiency. Secondly, a radial basis function based parametrisation was set up to allow the creation of single squealer line using the flat tip blade as a baseline geometry. The optimum case proved to increase efficiency 0.46% compared to the flat tip. After that, a combination of winglet and topology free squealer tips was investigated for topology optimisation. The winglet tip was parametrized as in the winglet only optimisation cases and topology free squealer walls were created using mapping of radial basis function surfaces of different complexities. It is shown that by combining both winglet and novel squealer topology optimisation, better designs of different topologies can be produced.
Low DP FlameSheet™ Extended Validation of a Flexible, Low Emissions, Higher Output and Efficiency F-Class Turbine Upgrade
Authors: Rizkalla Hany , Hui Timothy , Hernandez Fred , Yaquinto Matthew , KeshavaBhattu Ramesh 
Published: January 2021

Abstract
Renewables proliferation in the energy market is driving the need for flexibility in gas fired power plants to enable a wider and emissions compliant operability range. The ability for a gas fired plant to peak fire while maintaining emissions compliance, full life interval capability, improved simple and combined cycle heat rate and the ability to achieve extended turndown, positions a gas fired asset to benefit from an improved capacity factor, and overall economic viability in an increasingly renewables’ dependent energy market. The low pressure drop FlameSheet™ combustor variant’s implementation alongside PSM’s Gas Turbine Optimization Package (GTOP3.1) on a commercially operating frame 7FA heavy duty gas turbine in 2018 and as introduced in GT2019-91647, is presented with emphasis on extended validation of operational and emissions/tuning performance at different ambient conditions, higher peak firing and minimum load after one year of continuous commercial operation. The output and heat rate improvement achieved with the FlameSheet™/GTOP3.1 conversion thus enabling improved capacity is also discussed. As shale gas continue to grow as a dominant source of the U.S Natural gas supply, the need for fuel flexible combustion systems enabling tolerance to higher ethane/ethylene concentrations associated with Shale gas is required for improved operability. The adverse impact and means to mitigate such higher ethane/ethylene content on standard F-Class heavy duty combustion systems is also presented as part of said FlameSheet™/GTOP 3.1 conversion.
Flow in a Simulated Turbine Blade Cooling Channel With Spatially Varying Roughness Caused by Additive Manufacturing Orientation
Authors: McClain Stephen T. , Hanson David R. , Cinnamon Emily , Snyder Jacob C. , Kunz Robert F. , Thole Karen A. 
Published: January 2021

Abstract
Because of the effects of gravity acting on the melt region created during the laser sintering process, additively manufactured surfaces that are pointed upward have been shown to exhibit roughness characteristics different from those seen on surfaces that point downward. For this investigation, the Roughness Internal Flow Tunnel (RIFT) and computational fluid dynamics models were used to investigate flow in channels with different roughness on opposing walls of the channel. Three rough surfaces were employed for the investigation. Two of the surfaces were created using scaled, structured-light scans of the upskin and downskin surfaces of an Inconel 718 component which was created at a 45° angle to the printing surface and documented by Snyder et al. [1]. A third rough surface was created for the RIFT investigation using a structured-light scan of a surface similar to the Inconel 718 downskin surface, but a different scaling was used to provide larger roughness elements in the RIFT. The resulting roughness dimensions (Rq/Dh) of the three surfaces used were 0.0064, 0.0156, and 0.0405. The friction coefficients were measured over the range of 10,000 &lt; ReDh &lt; 70,000 for each surface opposed by a smooth wall and opposed by each of the other rough walls. At multiple ReDh values, x-array hot film anemometry was used to characterize the velocity and turbulence profiles for each roughness combination. The friction factor variations for each rough wall opposed by a smooth wall approached complete turbulence. However, when rough surfaces were opposed, the surfaces did not reach complete turbulence over the Reynolds number range investigated. The results of inner variable analysis demonstrate that the roughness function (ΔU+) becomes independent of the roughness condition of the opposing wall providing evidence that Townsend’s Hypothesis holds for the relative roughness values expected for additively manufactured turbine-blade cooling passages.
A Strategy to Tune Acoustic Terminations of Single-Can Test-Rigs to Mimic Thermoacoustic Behavior of a Full Engine
Authors: Haeringer Matthias , Fournier Guillaume J. J. , Meindl Max , Polifke Wolfgang 
Published: January 2021

Abstract
Thermoacoustic properties of can-annular combustors are commonly investigated by means of single-can test-rigs. To obtain representative results, it is crucial to mimic can-can coupling present in the full engine. However, current approaches either lack a solid theoretical foundation or are not practicable for high-pressure rigs. In the present study we employ Bloch-wave theory to derive reflection coefficients that correctly represent can-can coupling. We propose a strategy to impose such reflection coefficients at the acoustic terminations of a single-can test-rig by installing passive acoustic elements, namely straight ducts or Helmholtz resonators. In an iterative process, these elements are adapted to match the reflection coefficients for the dominant frequencies of the full engine. The strategy is demonstrated with a network model of a generic can-annular combustor and a 3D model of a realistic can-annular combustor configuration. For the latter we show that can-can coupling via the compressor exit plenum is negligible for frequencies sufficiently far away from plenum eigenfrequencies. Without utilizing previous knowledge of relevant frequencies or flame dynamics, the test-rig models are adapted within a few iterations and match the full engine with good accuracy. Using Helmholtz resonators for test-rig adaption turns out to be more viable than using straight ducts.
An Approach to Model a Lossless Junction for Fluid Network Calculations in Turbomachinery
Authors: Khandrymailov Andrii , Moroz Leonid , Yevlakhov Viktor , Staple Shanel , Vogel Gregory 
Published: January 2021

Abstract
Turbine secondary flow system calculations are usually performed by utilizing the thermal-fluid network approach. The network consists of branches and nodes. Fluid branches usually describe the flow resistance of the correspondent fluid path section, while fluid nodes are used to connect fluid branches between each other. Fluid flow in branches and nodes is described by the set of conservation equations such as mass and momentum equations. For fluid nodes, usually total or static pressure is used as a variable in these equations. However, such an approach may yield a system of equations that cannot be solved (for theoretical cases where zero resistance branches are present) or may produce significant differences in results compared to the more precise CFD solution (for real cases with resistances). This paper provides an approach on how to create a model of a fluid lossless junction in order to solve the mentioned problems. Such a junction enables the connection of any number of inflow and outflow fluid branches without bringing any flow resistance, which allows fluid branches to handle flow resistance influence by themselves.
The proposed model is based on the idea, that each node should contain not just one pressure (static or total) as a variable, but two variables — both static and total pressures. Such a node can be used to model junctions of different types with flow mixing, as well as separation and sudden cross-sectional area changes. With this approach it is also possible to model chambers by modifying just one equation. Also, this new method can be applied for both compressible and incompressible calculation types and can handle chocked flows as well.
Advanced Automated GT26 Combustion Tuning for Increased Operational Flexibility and Performance
Authors: Singla G. , Delatti B. , Scarpato A. , Barracas J. , Wang W. , Demougeot N. 
Published: January 2021

Abstract
Today’s advanced Gas Turbine (GT) combustion systems are designed to achieve low emission limits over a wide operational range. Regular combustion tuning is usually required to ensure that emissions are kept well within the plant compliance limits and that combustion dynamics levels are low enough to meet the mechanical integrity targets of all hot gas parts. These targets must be met during the full lifetime of the power plant, regardless of ambient conditions, fuel composition or engine degradation. Considering also the recent increase of combustor inspection intervals and the change in the GT loading profile due to the intermittent nature of renewable energies, it became advantageous to develop an automated GT26 combustion tuning control.
Ansaldo Energia self-learning AutoTune system, based on the well proven product developed by Power Systems Manufacturing (PSM), tunes engine operating parameters to maintain emission and combustion dynamics within specified limits under varying ambient conditions, load ranges, gas compositions and increasing engine degradation. It increases the robustness of the operation concept by introducing dynamic set points instead of fixed settings. This results in tuning flexibility, continuous engine optimization and it helps to potentially eliminate manual engine adjustments during a major inspection cycle.
After a general introduction on the operating concept of the GT26, the interaction between AutoTune and the GT controller is described together with the set-up and tuning principles. The universal AutoTune algorithm was adapted to the unique GT26 reheat architecture and flexibility, allowing for: (i) GT26 EV and SEV tuning for emissions and pulsations during stable conditions, (ii) tuning to minimize the minimum environmental load (MEL) with changing fuel gas properties or ambient temperature with the Low Part Load (LPL) concept, (iii) handling of very reactive fuels with high C2+ concentrations, (iv) tuning during transient conditions accounting for the variation of the GT thermal state. Based on robust experience after five successful GT26 installations, tuning attempts and successful tunings are statistically analyzed on a commercial plant over a period of several weeks to demonstrate the enlarged operational flexibility and performance of the GT26 equipped with AutoTune. The data analysis focuses on the Low Part Load operation, where Autotune achieved a robust decrease of MEL of 20MW, corresponding to a reduction of 4% in terms of combined cycle relative load.
Transonic Axial Compressors Loss Correlations: Part II — Loss Models Validation
Authors: Manfredi Marco , Babin Cedric , Fontaneto Fabrizio 
Published: January 2021

Abstract
The quest for greener, more efficient aircraft engines is the main driver for the development of innovative compression system designs. Reduced order design tools rely nevertheless on semi-empirical loss models, whose validity range is often not net or in general not verified. The present work aims at defining a set of loss correlations, which could readily be employed in the analysis and design process of modern transonic axial compressors. In Part I, various loss correlations were deeply described and, in some cases, updated to enhance both their generality and their prediction capability. In Part II, the effectiveness of both original and updated models will be tested for one specific low aspect ratio axial compressor stage. Experimental and numerical data will be used at such extent.
Numerical Investigation of 100% Premixed Hydrogen Combustor at Gas Turbines Conditions Using Detailed Chemistry
Authors: Menon Sachin , Bouten Thijs , Withag Jan , Klein Sikke , Gangoli Rao Arvind 
Published: January 2021

Abstract
The combustion properties of hydrogen make premixed hydrogen-air flames prone to flashback. Several combustor concepts have been proposed and studied in the past few years to tackle the problem of flame flashback in premixed high hydrogen fuel combustors. This study looks at one of the concepts which uses the Aerodynamically Trapped Vortex to stabilize the flame. Burner concepts based on trapped vortex flame stabilization have a higher resistance towards flame blowout than conventional swirl stabilized burners. This work looks at the flow and flame behavior in the proposed Aerodynamically Trapped Vortex Combustor for 100% premixed hydrogen operation. Numerical simulations for the analysis were performed with the commercial CFD simulation package AVL FIRE™. The flow field characterization was focused on the investigation of the influence of both the inlet velocity and inlet turbulence intensity on the mean velocity, wall velocity gradient and turbulence intensity in the combustor. To study the flame stabilization mechanism, reactive simulations were performed at two fuel equivalence ratios. The combustion regime of the flame, turbulent flame speed and temperature distribution in the combustor were quantified from the simulation results.
Combustion is modelled using a detailed chemistry solver with the k–ε turbulence model to resolve turbulence. No additional turbulence-chemistry interaction model is used in the current research. To reduce chemistry computational time, the multi-zone method is employed. To capture the effect of preferential diffusion, two approaches were used to quantify the diffusion coefficient of each species. The diffusion coefficients were calculated using both mixture averaged approach and the multi component diffusion approach. The proposed design for the Aero-dynamically Trapped Vortex combustor was able to stabilize a 100% premixed hydrogen flame without flashback for the simulated conditions.