bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic Response of Acoustically Forced Turbulent Premixed Biogas Flames
Authors: Ajetunmobi Oluwaseun , Talibi Midhat , Balachandran Ramanarayanan 
Published: November 2019

Abstract
Increasing demand for energy and the need for diversification of fuels used in gas turbine power generation is continuing to drive forward the development of fuel-flexible combustion systems, with particular focus on biomass derived sustainable fuels. The technical challenges arising from burning sustainable fuels are largely associated with the change in the chemical, thermal and transport properties of these fuels due to the variation of the constituents and their impact on the performance of the combustor including emissions, static and dynamic stabilities. There is a lack of detailed understanding on the effect of fuel composition on the flame sensitivity to acoustic and flow perturbations.
This paper describes an experimental study investigating the acoustic flame response of simulated biogas (methane/carbon dioxide/air mixtures) turbulent premixed flames. The effect of variation in carbondioxide, CO2, content on the flame response was quantified. Special emphasis was placed on understanding the dependence of this flame response on the amplitude of the acoustic forcing. The flame was subjected to strong velocity perturbations using loud speakers.
It was observed that the addition of CO2 had considerable influence on the magnitude of heat release response. The magnitude and the phase of flame describing function indicated that the mechanism of saturation in these flames for all conditions tested were the same. The difference in magnitude could been attributed to dilution effect and hence further investigation were carried out with N2 and Ar to clarify the role of CO2. The results indicate that the thermal capacity of the diluent gases could be playing a significant role in nonlinear flame dynamics.
Comparative Analysis of Detailed and Reduced Chemical Models of N-Dodecane
Authors: Zheng Chenwei , Eldeeb Mazen A. , Coombs Deshawn , Akih-Kumgeh Benjamin 
Published: November 2019

Abstract
For the purposes of combustion analysis, n-dodecane is used as the surrogate or a surrogate component for biodiesel and jet fuel. In order to capture kinetic effects in computational combustion, detailed and reduced models of n-dodecane are therefore used. This paper presents a comparative analysis of selected detailed chemical kinetic models of n-dodecane as well as reduction of these detailed models to more compact skeletal versions. The selected models are compared based on their ability to predict ignition phenomena. Measured ignition delay times from the literature are used as references. Both low- and high-temperature ignition simulations are considered. To further facilitate future computational combustion analysis, the detailed models are reduced using the Alternative Species Elimination (ASE) approach reported by Akih-Kumgeh and Bergthorson (Energy & Fuels, 2316–2326, 2013). The resulting skeletal models are compared in terms of their retained species, ranked species sensitivities, and kinetic parameters of the key reactions. Furthermore, within the framework of this paper, another model reduction technique is explored. The aim of this method is to further decrease model reduction time since this is often considered as a weakness of the otherwise effective ASE method. The resulting models from this exploratory reduction approach are compared with those obtained from the ASE method in terms of species retained and the accuracy with which combustion properties from the detailed models are predicted. Further chemical kinetic analysis of the reduced models is carried out with the aim of explaining observed similarities and differences.
Effect of Deterministic and Continuous Design Space Resolution on Multiple-Objective Combustor Optimization
Authors: Briones Alejandro M. , Rumpfkeil Markus P. , Thomas Nathan R. , Rankin Brent A. 
Published: November 2019

Abstract
A supervised machine learning technique namely an Adaptive Multiple Objective (AMO) optimization algorithm is used to divide a continuous and deterministic design space into non-dominated Pareto frontier and dominated design points. The effect of the initial training data quantity, i.e., computational fluid dynamics (CFD) results, on the Pareto frontier and output parameter sensitivity is explored. The optimization study is performed on a subsonic small-scale cavity-stabilized combustor. A parametric geometry is created using CAD that is coupled with a meshing software. The latter automatically transfers meshes and boundary conditions to the solver, which is coupled with a post-processing tool. Steady, incompressible three-dimensional simulations are performed using a multi-phase realizable k-ε Reynolds-averaged Navier-Stokes (RANS) approach with an adiabatic flamelet progress variable (FPV). Scalable wall functions are used for modeling turbulence near the wall. For each CFD simulation four levels of adaptive mesh refinement (AMR) are utilized on the original cut-cell grid. The mesh is refined where the flow exhibits large progress variable curvature. There are fifteen geometrical input parameters and three output parameters, viz., a pattern factor proxy (maximum exit temperature), a combustion efficiency proxy (averaged exit temperature), and total pressure loss (TPL). The Pareto frontier and the input-to-output parameter sensitivities are reported for each meta-model simulation. For the investigated design space, three times the number of input parameters plus one (48) yields an optimization independent of the initial sampling. This conclusion is drawn by comparing the Pareto frontiers and global sensitivities. However, the latter provides a better metric. The relative influence of the input parameters on the outputs is assessed by using both a Spearman’s order-rank correlation approach as well as an active subspace analysis. In general, non-dominated design points exhibit persistent geometrical features such as offset opposed cavity forward and aft driver jet alignment. Larger cavities necessitate larger chutes and smaller outer liner jet diameters, whereas smaller cavities require smaller chutes and larger outer liner jet diameters. The fuel injector radial location varies, but can be located either radially inward or outward with respect to the forward dilution jet radial locations. For these non-dominated designs there is substantial burning inside and outside of the cavity. The downstream dilution jets quench the upstream hot gases.
An Investigation of Laminar Flame Speed of CH4-O2-CO2 Mixtures
Authors: Turner Mattias A. , Paschal Tyler , Kulatilaka Waruna D. , Petersen Eric L. 
Published: November 2019

Abstract
The push for lower carbon emissions in power generation has driven interest in methods of carbon capture and sequestration. One such promising method involves the supercritical CO2 (sCO2) power cycle, a system which is powered by oxy-fuel combustion where supercritical carbon dioxide is used as the working fluid. The high CO2 concentration in the combustion products allows for relatively simple extraction of CO2 from the system. Although this is an active field of research, the design of such a combustor requires continued study of oxy-fuel combustion in high levels of CO2 diluent. With that objective in mind, laminar flame experiments were conducted for CH4-O2-CO2 mixtures at one atmosphere and room temperature, where the relative concentrations of O2 and CO2 in the oxidizer mixture were 34.0% and 66.0% by mole, respectively. These concentrations were chosen to ensure the flame would propagate quickly enough to overcome the effects of buoyancy, which were observed to become significant below laminar flame speeds of roughly 15 cm/s. A high-speed chemiluminescence imaging diagnostic was employed in place of the traditional schlieren technique. Laminar flame speed was measured from OH* emission at 306 nm for a full range of equivalence ratios, varying from 15.2 cm/s at 0.7 to 24.8 cm/s at stoichiometric. Additionally, images of OH* chemiluminescence of turbulent CH4-O2-CO2 flames and of quiescent, 5-atm CH4-O2-CO2 flames at stoichiometric concentration are also presented. These experiments provide useful data for validation of chemical kinetics models for oxy-methane combustion in a CO2 diluent, which can be applied to the modeling of oxy-methane combustion for supercritical CO2 power cycles.
Strongly Coupled Thermo-Mechanical Casing/Abradable Model for Rotor/Stator Interactions
Authors: Nyssen Florence , Vadcard Thibaut , Piollet Elsa , Batailly Alain 
Published: November 2019

Abstract
Modern turbomachine designs feature reduced nominal clearances between rotating bladed-disks and their surrounding casings in order to improve the engine efficiency. Unavoidably, clearance reduction increases the risk of contacts between static and rotating components which may yield hazardous interaction phenomena. In this context, the deposition of an abradable coating along the casing inner surface is a common way to enhance operational safety while mitigating interaction phenomena thus allowing for tighter clearances. Nonetheless, interactions leading to unexpected wear removal phenomena between a bladed-disk and a casing with abradable coating have been observed experimentally. Beside of blade damages such as cracks resulting from high amplitudes of vibration, experimental observations included very significant temperatures increase, particularly within the abradable coating, to a point that thermo-mechanical effects may not be neglected anymore. The aim of this work is to investigate the numerical modeling of thermal effects in the abradable coating and the casing due to contact interactions. In particular, the proposed model provides insight on the sensitivity of engines to contact events when the plane had reduced tarmac times between two consecutive flights.
A strongly coupled thermo-mechanical model of the casing and its abradable coating is first described. A 3D cylindrical mesh is employed, it may be decomposed in two parts: (1) along the casing contact surface, a cylindrical thermal mesh is constructed to compute the temperature elevation and heat diffusion in the three directions of space within the abradable coating, and (2) the casing itself is represented by a simplified cylindrical thermo-mechanical mesh to compute both temperature elevation and the induced deformations following temperature changes. This 3D hybrid mesh is combined with a mechanical mesh of the abradable layer, dedicated to wear modeling and the computation of normal and tangential contact forces following blade/abradable coating impacts. The heat flux resulting from contact events is related to the friction forces and only heat transfer by conduction is considered in this work. In order to reduce computational times, the time integration procedure is twofold: the explicit time integration scheme featuring reduced time steps required for contact treatment is combined with a larger time step time integration scheme used for the casing thermo-mechanical model. An extensive validation procedure is carried out from a numerical standpoint, it underlines the convergence of the model with respect to time and space parameters.
Strain Gage Ramifications on Mistuning in As-Manufactured Models and Experimental Testing
Authors: Gillaugh Daniel L. , Kaszynski Alexander A. , Brown Jeffrey M. , Beck Joseph A. , Slater Joseph C. 
Published: November 2019

Abstract
Blade mounted strain gages are vital during rig and engine development to ensure safe engine operation. However, they also enable a change in dynamics of integrally bladed rotors (IBR). State-of-the-art IBR dynamic response predictions are accomplished using as-manufactured models (AMM) generated via optical topography measurements and mesh morphing. Two AMM finite element models (FEMs) are created of a 20 bladed IBR. One FEM has no strain gages present, where the second FEM includes strain gages on six blades. Traditionally, strain gages and lead wires are treated as the same material property as the IBR itself. It will be shown that the inclusion of strain gages in AMM’s using this method changes the IBR’s predicted mistuning. An alternative AMM approach is developed that changes the material properties of the finite elements attributed to the strain gages. The predicted mistuning for each AMM is accomplished using the Fundamental Mistuning Model (FMM ID), where the predicted mistuning will be compared to both Traveling Wave Excitation (TWE) experiments and a rotating, single stage compressor rig. Findings show mistuning predictions of the non-strain gaged AMM compare far better to the experiments compared to the inclusion of the strain gages in the AMM. Additionally, altering material properties of the strain gages in the AMM improves mistuning prediction compared to treating the strain gages as the parent IBR material. Therefore, AMM should be acquired using clean, non-strain gaged rotors or the material properties of strain gaged elements need to be altered to more accurately model the component.
CFD Investigation of the Multiple Rotors Darrieus Type Turbine Performance
Authors: Mohamed Omar Sherif , Ibrahim Ahmed , El Baz Ahmed M. R. 
Published: November 2019

Abstract
The last few years have witnessed researches concerned by vertical axis wind turbine (VAWT) performance considering its advantages compared to the horizontal axis wind turbines, as it can be operated in urban areas without producing noise, ease of maintenance and simple construction, in addition to its low cost. More interest is growing in developing efficient clusters of VAWT in order to increase power generation at specific sites by using multiple turbines. In the present work, the performance of various configurations of Darrieus type VAWT clusters is examined using computational fluid dynamics (CFD) simulations. The objective of this work is to increase the overall power coefficient of the turbines cluster compared to single rotor performance. This objective shall be achieved by examining mutual interactions between rotors arranged in close proximity and examining the effect of oblique angle between rotors on overall performance of the cluster of rotors. The performance is assessed by observing the overall power coefficient of the cluster. Also, the velocity wake of the simulated three rotors turbine cases was analyzed and compared to the that of the single rotor.
Leakage and Cavity Pressures in an Interlocking Labyrinth Gas Seal: Measurements vs. Predictions
Authors: San Andrés Luis , Wu Tingcheng , Barajas-Rivera Jose , Zhang Jiaxin , Kawashita Rimpei 
Published: November 2019

Abstract
Gas labyrinth seals (LS) restrict secondary flows (leakage) in turbomachinery and their impact on the efficiency and rotordynamic stability of high-pressure compressors and steam turbines can hardly be overstated. Amongst seal types, the interlocking labyrinth seal (ILS), having teeth on both the rotor and on the stator, is able to reduce leakage up to 30% compared to other LSs with either all teeth on the rotor or all teeth on the stator. This paper introduces a revamped facility to test gas seals for their rotordynamic performance and presents measurements of the leakage and cavity pressures in a five teeth ILS. The seal with overall length/diameter L/D = 0.3 and small tip clearance Cr/D = 0.00133 is supplied with air at T = 298 K and increasing inlet pressure Pin = 0.3 MPa ∼ 1.3 MPa, while the exit pressure/inlet pressure ratio PR = Pout/Pin is set to range from 0.3 to 0.8. The rotor speed varies from null to 10 krpm (79 m/s max. surface speed). During the tests, instrumentation records the seal mass flow (ṁ) and static pressure in each cavity. In parallel, a bulk-flow model (BFM) and a computational fluid dynamics (CFD) analysis predict the flow field and deliver the same performance characteristics, namely leakage and cavity pressures. Both measurements and predictions agree closely (within 5%) and demonstrate the seal mass flow rate is independent of rotor speed. A modified flow factor Φ¯=m.T/PinD1-PR2 characterizes best the seal mass flow with a unique magnitude for all pressure conditions, Pin and PR.
A Constitutive Model for Predicting Modified Creep Strain Rates due to Cyclic Loading of Gas Turbine Components
Authors: Green Richard , Douglas Jonathan , Moffat Andrew , Scaletta Brent 
Published: November 2019

Abstract
The traditional approach to the design of industrial Gas Turbines considers base load operation. This assumption is no longer applicable as owner operators require more operational flexibility and increased availability and reliability. Flexibility in operation manifests as increased cyclic loading and variations in on and off load dwell periods and thermal loads. These complex loading profiles inevitably lead to damage from both creep and fatigue, and interaction of these two damage mechanisms over the duration of the service interval. These interactions can result in higher average creep rates and more damage than expected.
Robust, path dependent modeling approaches are required to better understand the effects of flexible operation on material response and subsequent damage. Moreover, a unified approach to creep-fatigue is significantly more effective at capturing this behavior.
There are several types of interactions that can drive additional damage. These include relatively well understood mechanisms, such as the effect of plasticity on primary creep and the effect of creep dwells on cyclic material properties. Other interactions that are less well understood include interruptions to the load during creep dwells and the effects of off-load periods on the overall creep rate.
This paper considers a constitutive approach to predict the modified creep rate due to load interruptions and off-load dwells using a backstress model. The backstress model is included in the calculation of inelastic strain rate equations, using a Chaboche type formulation. The model has been fitted to conventional material test data for typical superalloys used in gas turbine applications. To validate the approach, forward creep tests were conducted with varying interruptions to the load during the creep dwell period. These tests show a reduction in creep life and an increase in overall creep rate, when compared with the results for a constant stress and temperature condition. Previous work, presented by the authors [1], outlined a hypothesis that attributes the increase in overall creep rate to the influence of a recovery potential stress. This paper presents the subsequent work which demonstrates that the recovery potential stress can be defined by the difference between the applied stress and the backstress. It is shown that the dwell period between reload cycles is critical for calculating the recovery potential and overall creep rate.
NASA’s Role in Gas Turbine Technology Development: Accelerating Technical Progress via Collaboration Between Academia, Industry, and Government Agencies
Authors: Suder Kenneth L. 
Published: November 2019

Abstract
Given the maturity of the gas turbine engine since its invention and also considering the limited and flattened level of resources expected to be allocated for NASA aeronautics research and development, we ask the question are NASA technology investments still needed to enable future turbine engine-based propulsion systems? If so, what is NASA’s unique role to justify NASA’s investment? To address this topic, we will first review the accomplishments and the impact that NASA Glenn Research Center has made on turbine engine technologies over the last 78 years. Specifically, this paper discusses NASA’s role and contributions to turbine engine development, specific to both 1) NASA’s role in conducting experiments to understand flow physics and provide relevant benchmark validation experiments for Computational Fluid Dynamics (CFD) code development, validation, and assessment; and 2) the impact of technologies resulting from NASA collaborations with industry, academia, and other government agencies. Note that the scope of the discussion is limited to the NASA technology contributions with which the author was intimately associated, and does not represent the entirety of the NASA contributions to turbine engine technology. The specific research, development, and demonstrations discussed herein were selected to both 1) provide a comprehensive review and reference list of the technology and its impact, and 2) identify NASA’s unique role and highlight how NASA’s involvement resulted in additional benefit to the gas turbine engine community.
Secondly, we will discuss current NASA collaborations that are in progress and provide a status of the results. Finally, we discuss the challenges anticipated for future turbine engine-based propulsion systems for civil aviation and identify potential opportunities for collaboration where NASA involvement would be beneficial. Ultimately, the gas turbine engine community will decide if NASA involvement is needed to contribute to the development of the design and analysis tools, databases, and technology demonstration programs to meet these challenges for future turbine engine-based propulsion systems.
A Critical Plane Approach for LCF Evaluation of Gas Turbine Disks and Rotors
Authors: Riva Andrea , Riazantsev Sergei , Foletti Stefano , Beretta Stefano 
Published: November 2019

Abstract
In order to safely increase gas turbine efficiency without issues of early damage and failures, component life evaluation must neither be too conservative nor too optimistic. The method used for designing the parts is supposed to be as accurate as possible, so that the subsequent application of the appropriate statistically defined safety factors will not excessively reduce the component life estimation. In order to achieve such important targets, all phenomena that can be detrimental for fatigue damage, such as multiaxiality and non-proportionality, need to be properly addressed by the Low Cycle Fatigue (LCF) assessment method. In particular, high temperature gas turbine rotating parts are characterized by a superposition of thermal and centrifugal stresses, which act in the same location but along different directions (i.e. multiaxiality) in different moments of the start-up/base-load/shut-down cycle (i.e. non-proportionality).
In this framework, critical plane approaches are the most appropriate methods for an accurate and reliable low cycle fatigue life estimation. These methods search the most critical plane where the greatest damage will be accumulated by defining a damage parameter that is calculated for all planes. Among several methods developed in the academic community and considered in this work, the Fatemi-Socie method was identified as the most effective for the studied materials and components. The Fatemi-Socie damage parameter is a combination of in-plane shear strain and normal stress, which accounts for the fact that fatigue damage (of the materials object of the study) is developed along shear strain with an important contribution of tensile normal stress, which is responsible for crack opening and propagation.
An extensive testing campaign was performed to identify the most appropriate approach for the studied materials and to accurately fit all the model parameters. The testing campaign therefore included high temperature LCF tests and several types of multiaxial tests (tension-torsion, notched specimens, etc.).
Since the search for the critical plane can be demanding from the point of view of computing resources, an in-house software was developed with the scope of reducing the calculation time consistently with the speed required by the industrial design loops.
This paper will cover the background and the assumptions behind the development of a complete industrial workflow for the evaluation of LCF life of rotors and disks, prior to its systematic application for a significant number of Ansaldo components.