bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigations of Superheated and Supercritical Injections of Liquid Fuels
Authors: Yin Zhiyao , Kutne Peter , Eichhorn Jochen , Meier Wolfgang
Published: January 2021

Single- and multi-component liquid fuels are injected in a jet-in-coflow configuration at elevated temperatures and pressures with both a custom plain orifice nozzle and a commercial pressure-swirl atomizer. The transitions in spray morphology from mechanical breakup to superheated/supercritical regimes are characterized qualitatively by laser shadowgraphy and evaluated based on quantitative measures of superheat. Although fuel preheating exhibits no discernible effect in the mechanical breakup regime, dramatic jet-to-plume transition as well as build up of fuel vapor in the spray chamber are observed with increasing level of superheat. The difference between two different atomizers in terms of spray behavior diminishes at high levels of superheat, suggesting the predominant role of thermal effect on spray morphology in superheated/supercritical regimes. For a mutli-component fuel such as Jet A-1, the transition into a fully flashing spray occurs at temperatures lower than expected values, which are calculated by treating Jet A-1 as a single-component fuel. Additionally, pressure drop is shown as a sensitive indicator for the departure from mechanical breakup and the onset of thermal effect on the spray. Comparisons between measured and estimated pressure drop also reveal the differences in susceptibility to thermal effects between the plain orifice and the pressure-swirl atomizers.
Effect of Hydrogen on Steady-State and Transient Combustion Instability Characteristics
Authors: Strollo John , Peluso Stephen , O’Connor Jacqueline
Published: January 2021

This paper examines the effects of steady-state and transient hydrogen enrichment on thermoacoustic instability in a model gas turbine combustor. Combustion instability, a feedback loop between flame heat release rate oscillations and combustor acoustics, is characterized in a swirl-stabilized flame operated at a range of hydrogen-natural gas fuel blends and heat rates. Measurements of combustor chamber pressure fluctuations and CH* chemiluminescence imaging are used to characterize instability at a range of operating conditions. Steady-state tests show that both mixture heat rate and hydrogen content affect system stability. At a given heat rate, higher levels of hydrogen result in unstable combustion. As heat rate increases, instability occurs at lower concentrations of hydrogen in the fuel. Transient operation was tested in two directions — instability onset and decay — and two hydrogen-addition times — a short time of 1 millisecond and a longer time of 4 seconds. Results show that instability onset processes, through the transient addition of hydrogen, are highly repeatable regardless of the timescale of hydrogen addition. Certain instability decay processes are less repeatable, resulting in cases that do not fully transition from unstable to stable combustion despite similar changes in hydrogen fuel flow rate. Flame behavior before, during, and after the transient is characterized using high-speed CH* chemiluminescence imaging. Analysis of the high-speed images show changes in flame stabilization and dynamics during the onset and decay processes. The results of this study can have implications for systems that experience variations in fuel composition, particularly in light of growing interest in hydrogen as a renewable fuel.
Micromechanics Approach for the Overall Elastic Properties of Ceramic Matrix Composites Incorporating Defect Structures
Authors: Kumar Rajesh S.
Published: January 2021

Initial mechanical behavior of Ceramic Matrix Composites (CMCs) is linear until the proportional limit. This initial behavior is characterized by linear elastic properties, which are anisotropic due to the orientation and arrangement of fibers in the matrix. The linear elastic properties are needed during various phases of analysis and design of CMC components. CMCs are typically made with ceramic unidirectional or woven fiber preforms embedded in a ceramic matrix formed via various processing routes. The matrix processing of interest in this work is that formed via Polymer Impregnation and Pyrolysis (PIP). As this process involves pyrolysis process to convert a pre-ceramic polymer into ceramic, considerable volume shrinkage occurs in the material. This volume shrinkage leads to significant defects in the final material in the forms of porosity of various size, shape, and volume fraction. These defect structures can have a significant impact on the elastic and damage response of the material. In this paper, we develop a new micromechanics modeling framework to study the effects of processing-induced defects on linear elastic response of a PIP-derived CMC. A combination of analytical and computational micromechanics approaches is used to derive the overall elastic tensor of the CMC as a function of the underlying constituents and/or defect structures. It is shown that the volume fraction and aspect ratio of porosity at various length-scales plays an important role in accurate prediction of the elastic tensor. Specifically, it is shown that the through-thickness elastic tensor components cannot be predicted accurately using the micromechanics models unless the effects of defects are considered.
Unsteady Flow Simulation of an Axial Fan for Dry Cooling in a CSP Plant Using the Variational Multiscale Method
Authors: Barnabei Valerio Francesco , Castorrini Alessio , Corsini Alessandro , Van der Spuy Johan , Rispoli Franco
Published: January 2021

We present an unsteady simulation of an axial fan with low pressure and high flow rate, developed during the MinWaterCSP EU project, specifically designed and optimized for Concentrating Solar Power (CSP) plants with the aim of reducing water consumption at the condenser stage. An earlier version of the fan, referred as M-fan, was initially developed to serve the hybrid cooling system, to boost the overall heat transfer performance with dry cooling. In this work, we will performing a Computational Fluid Dynamics (CFD) analysis of the unsteady flow on a redesigned and scaled version of the M-fan, referred as T-fan, by The T-fan was designed and optimized to reduce noise emissions and improve efficiency with respect to the M-fan. We perform the simulation using an in-house built C++ parallel code for CFD analysis using Finite Elements (FE). We model the flow dynamics using the Residual Based Variational MultiScale method (RBVMS) to obtain a stabilized solution of the Navier-Stokes equation using FE discretization. We will discuss the simulation results of the RBVMS model by comparing our simulation of the T-fan with experimental results on the same fan.
A Numerical Investigation Into Secondary Flows at the Inlet to a Low-Pressure Compressor Transition Duct
Authors: Tsakmakidou Dimitra , Walker A. Duncan , Hall Chris
Published: January 2021

To reduce fuel-burn and CO2 emissions from aero gas turbines there is a drive towards very-high bypass ratio and smaller ultra-high-pressure ratio core engine technologies. However, this makes the design of the ducts connecting various compressor spools more challenging as the larger required radius change increases their aerodynamic loading. This is exacerbated for the duct which feeds the engine core as it must accept the relatively low-quality flow produced by the fan root. This is characterised by a hub-low pressure profile and large secondary flow structures which will inevitably increase loss and the likelihood of flow separation. This paper presents a numerical design study aimed at modifying an existing fully annular, low-speed test facility to produce larger, more representative rotor loss cores. The CFD domain comprises a single stage axial compressor and transition duct representative of the low-pressure spool in a high bypass ratio turbofan. The rotating and stationary frames were coupled using a sliding mesh and a uRANS approach with Reynolds Stress closure for the turbulence modelling. The methodology was first validated using existing experimental data before examining a number of parameters such as inlet boundary layer thickness, inlet swirl, tip gap, blade solidity, thickness, lean. It was found that a combination of an increased inlet hub boundary layer and a reduction in solidity sufficiently increased the hub loading and encouraged the development of significantly large loss cores. Preliminary CFD results also showed that the increased rotor loss cores promoted better mixing through the outlet guide which subsequently reduced hub boundary layer thickness and secondary flows. Despite incurring a larger total pressure loss this suggested that the transition duct moved further from stall and could therefore potentially be made shorter.
CMSX-4® Plus (SLS): An Improved 3rd Generation Single Crystal Alloy
Authors: Wahl Jacqueline , Harris Ken
Published: January 2021

Ongoing demand for advanced aero gas turbine engines with lower fuel burn and commensurate reduced CO2 emissions require single crystal (SX) superalloys capable of operating at higher gas and metal temperatures beyond the capability of 2nd generation, 3% rhenium (Re)-containing SX alloys, currently used extensively in commercial and military flight engines. These complex cooled turbine blades and vane castings must have an excellent balance of high temperature mechanical properties, producibility, oxidation/hot corrosion resistance, coating compatibility including TBC performance and phase stability.

The highest strength nickel-base SX superalloys currently in production (3rd generation CMSX-10K® and CMSX-10N® alloys) contain 6–7% Re. These highly alloyed, specialty alloys have some application drawbacks including some secondary reaction zone (SRZ) phase instability in the base alloy adjacent to the coatings, low temperature internal oxidation/hot corrosion attack requiring sophisticated dual role internal and external coatings and difficulty in production solution heat treatment. In addition, current 3rd generation SX alloys have relatively higher density which is a disadvantage in terms of weight and inertia in rotating part applications, and high cost due to the elevated Re content.

An improved, lower Re content (4.8%), 3rd generation SX superalloy, CMSX-4® Plus (SLS) has been developed with improved properties and performance over current 3rd generation SX alloys, while lacking the drawbacks. Coatings have been successfully developed which are compatible with the base alloy and suitable bond coats for TBC application. This paper presents the characterization of CMSX-4 Plus (SLS) alloy, including composition, mechanical and physical properties, oxidation properties and phase stability, along with production status.
Experimental and Kinetic Evaluation of Pressurized Lean Premixed Hydrogen-Air Flame Stability With Carbon Dioxide and Steam Dilution
Authors: Runyon Jon , Pugh Daniel , Giles Anthony , Goktepe Burak , Bowen Philip , Marsh Richard , Morris Steven
Published: January 2021

A study has been undertaken to experimentally and numerically evaluate the use of carbon dioxide or steam as premixed fuel additive in hydrogen-air flames to aid in the development of lean premixed (LPM) swirl burner technology for low NOx operation. Chemical kinetics modelling indicates that the use of CO2 or steam in the premixed reactants reduces H2-air laminar flame speed and adiabatic flame temperature within the well-characterized range of preheated LPM methane-air flames, albeit in markedly different proportions; for example, nearly 65 %vol CO2 as a proportion of the fuel is required for a reduction in laminar flame speed to equivalent CH4-air values, while approximately 30 %vol CO2 in the fuel is required for an equivalent reduction in adiabatic flame temperature, significantly impacted by the increased heat capacity of CO2. The 2nd generation high-pressure generic swirl burner, designed for use with LPM CH4-air, was therefore utilized to experimentally investigate the influence of CO2 and steam dilution on pressurized (up to 250 kW/MPa), preheated (up to 573 K), LPM H2-air flame stability using high-speed OH* chemiluminescence. In addition, exhaust gas emissions, such as NOx and CO, have been measured in comparison with equivalent thermal power conditions for CH4-air flames, showing that low NOx operation can be achieved. Furthermore, pure LPM H2-air flames are characterized for the first time in this burner, stabilized at low equivalence ratio (approximately 0.24) and increased Reynolds number at atmospheric pressure compared to the stable CH4-air flame (equivalence ratio of 0.55). The influence of extinction strain rate is suggested to characterize, both experimentally and numerically, the observed lean flame behavior, in particular as extinction strain rate has been shown to be non-monotonic with pressure for highly-reactive and diffuse fuels such as hydrogen.
Effect of Different Fuels on Combustion Instabilities in an Annular Combustor
Authors: Soundararajan Preethi Rajendram , Vignat Guillaume , Durox Daniel , Renaud Antoine , Candel Sébastien
Published: January 2021

Combustion instabilities in annular combustors of jet engines is a recurring issue. In the present study, the characteristics of instabilities for different fuels are investigated by combining the instability maps obtained in an annular combustor equipped with multiple swirling spray injectors (MICCA-Spray) and flame describing functions (FDFs) from a single sector configuration (SICCA-Spray). Two types of liquid fuels are injected as hollow cone sprays: heptane, which is fairly volatile, and dodecane, which is less volatile. Experiments are also conducted with gaseous propane, perfectly premixed with air, which serves as a reference. An instability map is systematically drawn by varying the global equivalence ratio and thermal power. The data indicate that the amplitude and frequency of instabilities depend, for the same operating point, on the fuel injection conditions (premixed or spray) and fuel type. Overall trends show that premixed propane is unstable in a broad operating domain. Injection of liquid fuels induces changes in time lag that modify the unstable regions. For heptane the instability map is closer to the propane reference map whereas dodecane exhibits wider stable regions. Variations can also be observed in the behavior of spin ratio that characterizes the azimuthal structure of the coupling mode. An attempt is made to understand these features by examining the FDF, which gives the ratio of relative fluctuations in heat release rate to the relative fluctuations in velocity. The FDFs measured in a single sector configuration gives access to gain and phase information that can be used to determine unstable bands. It is found that based on whether the MICCA-Spray instability frequency is within these bands, the instability amplitude can be high or low. This indicates that the difference in instabilities between the three fuels can be linked to the variations in FDFs.
Multi-Jet Impingement Heat Transfer With a Dimple-Pimple Patterned Jet Plate
Authors: Zawati Husam , Gupta Gaurav , Khlyapov Yakym , Fernandez Erik , Kapat Jayanta , Schaenzer Megan , Rodriguez Jose
Published: January 2021

The objective of the present study is the evaluation of the heat transfer difference between a novel jet plate configuration and a conventional flat jet orifice plate. Physical mechanisms that lead to a change in Nusselt number when comparing both configurations are discussed in two regions: impingement and crossflow. In the presented work, both plates with identical inline arrays of (20 × 26) circular air jets impinging orthogonally on a flat target comprised of 20 segments parallel to the jet orifice plates, are studied. The first is a staggered configuration of a pimple-dimple (convex-concave) plate. This plate features two jet diameters: (a) 4.63 mm emanating from negative sphere of 14.63 mm in radius inward imprint; (b) 2.19 mm emanating from a positive sphere of 17.07 mm in radius, protruding from the base of the plate. The second jet plate is flat, which serves as a baseline for the heat transfer study. This plate has a constant jet orifice diameters of 3.49 mm, found based on the definition of total average open area of the first plate (NPR configuration).

Heat transfer characteristics and turbulent flow structures are investigated over jet-averaged Reynolds numbers (Reav,j) of 5,000, 7,000, and 9,000. Jet-to-plate distance (Z/Dj) is varied between (2.4 – 6.0) jet diameters. A numerical study is carried out to compare various turbulence models (κε-EB, κε-Lag EB, κε-v2f, κω-SST, RST). Numerical simulations are analyzed in detail to explain the underlying mechanism of heat transfer enhancement, related to such geometries.

The convex-concaved plate yields lower globally-averaged heat transfer coefficients when compared to a flat jet plate in the impingement region. However, enhancement up to 23% is seen in the crossflow region, where the crossflow effects are dominant in a maximum-crossflow configuration.
Some Observations on the Computational Sensitivity of Rotating Cavity Flows
Authors: Hickling Tom , He Li
Published: January 2021

Heat transfer inside rotating cavities plays an important role in gas turbine engineering. Flows in both compressors and turbine internal flow cavities exhibit self-generated large-scale inertial wave structures, and buoyancy effects are often important. Across the open literature on the topic, there seems to be no clear consensus on what the most suitable modelling fidelity is — although it is a widely held opinion that URANS approaches are less suitable than LES, many authors have succeeded in getting reasonable heat transfer results with URANS. There is also little knowledge of the validity of hybrid URANS/LES type approaches (such as DES) when it comes to predicting the heat transfer in these flows, and furthermore, on the sensitivity of the flow model validity to local driving aerothermal mechanisms in different parts of the cavity.

This paper presents the results of a systematic investigation of a rotating cavity with axial throughflow at a Grashof number of 3 × 109. It is found that, for the case investigated, the disk Ekman layers remain laminar. This causes the disk heat transfer to be relatively insensitive to the modelling fidelity used with URANS, DES, and LES giving similar results. The effect of the disk thermal boundary condition is also investigated — it is found to have a significant effect on the direction of the near-wall flow at high radii, despite the large-scale flow structure within the cavity remaining essentially unchanged. This feedback of the disk heat transfer to the near-disk aerodynamics implies that conjugate heat transfer computations of rotating cavities may be worth investigating. On the shroud, URANS fails to resolve the heat transfer enhancement from small-scale buoyancy driven streaks, whilst these are captured by LES. DES also captures these streaks, as the URANS layer within which they are located returns a very small eddy viscosity, and behaves in a similar manner to LES.
Calibration of a V-Cone for Low Mass Flows for Small Core Compressor Research
Authors: Stephens Julia E. , Kulkarni Sameer
Published: January 2021

Advancements in core compressor technologies are necessary for next generation, high Overall Pressure Ratio (OPR) turbofan engines. High pressure compressors (HPCs) for future engines are being designed with exit corrected mass flow rates less than 2.25 kg/s (5 lbm/s). In order to accurately measure the performance of these advanced designs, high accuracy measurements are needed in test facilities. The W7 High Speed Multistage Axial Compressor Facility at NASA Glenn Research Center has been used to acquire data for advanced compressor designs. This facility utilizes an advanced differential pressure flow meter called a V-Cone. The facility has historically tested components with physical mass flow rates in the range of 27 to 45 kg/s (60 to 100 lbm/s). As such, when the V-Cone was calibrated prior to installation, the calibrations focused on higher mass flow rates, and uncertainties in that regime range from 0.5% to 0.85%. However, for low mass flow rates under 9 kg/s (20 lbm/s), expected in tests of advanced high OPR HPCs rear stages, the uncertainties of the V-Cone exceed 2.5%. To address this, using a method similar to that utilized by the National Institute of Standards and Technology, an array of Critical Flow Venturi Nozzles (CFVs) was installed in the W7 test section and used to calibrate the V-Cone in 0.5 kg/s (1 lbm/s) increments up to 10.5 kg/s (23 lbm/s). This effort details the measurements and uncertainties associated with this calibration which resulted in a final uncertainty of the V-Cone measurements under 1%.
The Effect of Blade Count on Body Force Model Performance for Axial Fans
Authors: Saini Palak , Defoe Jeff
Published: January 2021

Body force models enable inexpensive numerical simulations of turbomachinery. The approach replaces the blades with sources of momentum/energy. Such models capture a “smeared out” version of the blades’ effect on the flow, reducing computational cost. The body force model used in this paper has been widely used in aircraft engine applications. Its implementation for low speed, low solidity (few blades) turbomachines, such as automotive cooling fans, enables predictions of cooling flows and component temperatures without calibrated fan curves. Automotive cooling fans tend to have less than 10 blades, which is approximately 50% of blade counts for modern jet engine fans. The effect this has on the body force model predictions is unknown and the objective of this paper is to quantify how varying blade count affects the accuracy of the predictions for both uniform and non-uniform inflow. The key findings are that reductions in blade metal blockage combined with spanwise flow redistribution drives the body force model to more accurately predict work coefficient as the blade count decreases, and that reducing the number of blades is found to have negligible impacts on upstream influence and distortion transfer in non-uniform inflow until extremely low blade counts (such as 2) are applied.
The Effect of the Degree of Premixedness on Self-Excited Combustion Instability
Authors: Howie Adam , Doleiden Daniel , Peluso Stephen , O’Connor Jacqueline
Published: January 2021

The use of lean, premixed fuel and air mixtures is a common strategy to reduce NOx emissions in gas turbine combustors. However, this strategy causes an increased susceptibility to self-excited instability, which manifests as fluctuations in heat release rate, flow velocity, and combustor acoustics that oscillate in-phase in a feedback loop. This study considers the effect of the level of premixedness on the self-excited instability in a single-nozzle combustor. In this system, the fuel can be injected inside the nozzle to create a partially-premixed mixture or far upstream to create a fully-premixed mixture, varying the level of premixedness of the fuel and air entering the combustor. When global equivalence ratio is held constant, the cases with higher levels of premixing have higher instability amplitudes. Highspeed CH* chemiluminescence imaging shows that the flame for these cases is more compact and the distribution of the heat release rate oscillations is more concentrated near the corner of the combustor in the outer recirculation zones. Rayleigh index images, which are a metric for quantifying the relative phase of pressure and heat release rate oscillations, suggest that vortex rollup in the corner region is primarily responsible for determining instability characteristics when premixedness is varied. This finding is further supported through analysis of local flame edge dynamics.
Application of Damage Mechanics and Polynomial Chaos Expansion for Lifetime Prediction of High-Temperature Components Under Creep-Fatigue Loading
Authors: Koelzow Felix , Khan Muhammad Mohsin , Kontermann Christian , Oechsner Matthias
Published: January 2021

Several (accumulative) lifetime models were developed to assess the lifetime consumption of high-temperature components of steam and gas turbine power plants during flexible operation modes. These accumulative methods have several drawbacks, e.g. that measured loading profiles cannot be used within accumulative lifetime methods without manual corrections, and cannot be combined directly to sophisticated probabilistic methods. Although these methods are widely accepted and used for years, the accumulative lifetime prediction procedures need improvement regarding the lifetime consumption of thermal power plants during flexible operation modes. Furthermore, previous investigations show that the main influencing factor from the materials perspective, the critical damage threshold, cannot be statistically estimated from typical creep-fatigue experiments due to massive experimental effort and a low amount of available data.

This paper seeks to investigate simple damage mechanics concepts applied to high-temperature components under creep-fatigue loading to demonstrate that these methods can overcome some drawbacks and use improvement potentials of traditional accumulative lifetime methods. Furthermore, damage mechanics models do not provide any reliability information, and the assessment of the resultant lifetime prediction is nearly impossible. At this point, probabilistic methods are used to quantify the missing information concerning failure probabilities and sensitivities and thus, the combination of both provides rigorous information for engineering judgment.

Nearly 50 low cycle fatigue experiments of a high chromium cast steel, including dwell times and service-type cycles, are used to investigate the model properties of a simple damage evolution equation using the strain equivalence hypothesis. Furthermore, different temperatures from 300 °C to 625 °C and different strain ranges from 0.35% to 2% were applied during the experiments. The determination of the specimen stiffness allows a quantification of the damage evolution during the experiment. The model parameters are determined by Nelder-Mead optimization procedure, and the dependencies of the model parameters concerning to different temperatures and strain ranges are investigated. In this paper, polynomial chaos expansion (PCE) is used for uncertainty propagation of the model uncertainties while using non-intrusive methods (regression techniques). In a further post-processing step, the computed PCE coefficients of the damage variable are used to determine the probability of failure as a function of cycles and evolution of the probability density function (pdf).

Except for the selected damage mechanics model which is considered simple, the advantages of using damage mechanics concepts combined with sophisticated probabilistic methods are presented in this paper.
Model Validation of an Euler-Based 2D-Throughflow Approach for Multistage Axial Turbine Analysis
Authors: Föllner Sebastian , Amedick Volker , Bonhoff Bernhard , Brillert Dieter , Benra Friedrich-Karl
Published: January 2021

In this paper the development and validation of a new meridional throughflow solver for the analysis of multistage axial turbines is presented. The quasi-three-dimensional finite-volume solver named tFlow is based on the inviscid Euler equations. To treat transonic flows with shocks the approximate Riemann solver of Roe for the computation of the inviscid fluxes in combination with the MUSCL approach are used. In the meridional plane turbine blades are numerically modeled by introducing two volume source terms for blade blockage and blade deviation effects.

In this contribution four different validation test-cases are discussed. The general fluid solver is validated by analytical solutions of the established Ringleb flow and the simulation of a two-dimensional transonic nozzle flow. In contrast to prior publications [1–3] tFlow uses a different formulation of the blockage effect which is tested using the blockage data of a general convergent-divergent nozzle. Blade deviation effects are validated by comparison with three-dimensional results obtained from the commercial flow solver CFX. The results of tFlow are consistent with the analytical solutions and in case of the blade deviation test-case in good agreement to the three-dimensional results. Compared to fully three-dimensional simulations the developed solver enables faster analyses of multistage axial turbines to evaluate the performance characteristic.
Experimental Investigation of the Starting Procedure of a Helicopter Gas Turbine Featuring an Impingement Quick-Start System
Authors: Kuen Niklas , Gümmer Volker
Published: January 2021

Intended Single Engine Operation (ISEO) offers fuel saving potential for twin engine helicopters but the shut-off of one engine implies safety concerns. Due to the restart time of the gas turbine the helicopter will experience a significant loss of altitude which limits the safe envelope where ISEO is applicable. In this paper, an air impingement system, which is capable of reducing the startup time of the engine by about 60 % to 80 %, is investigated experimentally. Different parameter variations are carried out to minimize the amount of air which is necessary to accelerate the engine in order to reduce the overall weight and size of the system. The modifications to the process are elaborated for startup of the engine to ground idle and to flight operation mode. For startup to ground idle the impinged air mass could be reduced by 25 % without having drawbacks in startup time.
Large Eddy Simulation of a Turbulent Spray Burner Using Thickened Flame Model and Adaptive Mesh Refinement
Authors: Rezchikova Aleksandra , Mehl Cédric , Drennan Scott , Colin Olivier
Published: January 2021

The accurate simulation of two-phase flow combustion is crucial for the design of aeronautical combustion chambers. In order to gain insight into complex interactions between a flame, a flow, and a liquid phase, the present work addresses the combustion modeling for the Large Eddy Simulation (LES) of a turbulent spray jet flame. The Eulerian-Lagrangian framework is selected to represent the gaseous and liquid phases, respectively. Chemical processes are described by a reduced mechanism, and turbulent combustion is modeled by the Thickened Flame Model (TFM) coupled to the Adaptive Mesh Refinement (AMR). The TFM-AMR extension on the dispersed phase is successfully validated on a laminar spray flame configuration. Then, the modeling approach is evaluated on the academic turbulent spray burner, providing a good agreement with the experimental data.
Heat Transfer Measurements Using Multiple Thermochromic Liquid Crystals in Symmetric Cooling Channels
Authors: Krille Tobias , Retzko Stefan , Poser Rico , von Wolfersdorf Jens
Published: January 2021

The transient Thermochromic Liquid Crystal (TLC) method is applied to determine the distribution of the local heat transfer coefficients using a configuration with parallel cooling channels at an engine relevant Reynolds number. The rectangular channels with a moderate aspect ratio and a high length-to-diameter ratio are equipped with one-sided oblique ribs with high blockage, which is a promising configuration for turbine near wall cooling applications. In this arrangement, the three inner channels should experience same flow and thermal conditions. Numerical simulations are performed to substantiate this assumption.

The symmetric single channels are sprayed with narrowband TLC with various indication temperatures. Multiple experiments were conducted. All start at ambient conditions before the fluid is heated up to several temperatures between 46°C and 73°C. The results show that the determined local heat transfer coefficients and therefore the Nusselt numbers vary significantly for the different experimental conditions especially at locations of high heat transfer coefficient behind the ribs. A simplified procedure with respect to measurement uncertainties is applied to enable an easy and fast valuation on the data quality. This might be used within the data reduction analysis for such experiments directly. The approach is illustrated using the obtained experimental data.
Development of a CFD-CSD Coupling Technique for Large Scale Offshore Wind Turbines
Authors: Pichitkul Auraluck , Sankar Lakshmi N.
Published: January 2021

Wind engineering technology has been continuously investigated and developed over the past several decades in response to steadily growing demand for renewable energy resources, in order to meet the increased demand for power production, fixed and floating platforms with different mooring configurations have been fielded, accommodating large-scale offshore wind turbines in deep water areas. In this study, the aerodynamic loads on such systems are modeled using a computational structural dynamics solver called OpenFAST developed by National Renewable Energy Laboratory, coupled to an in-house computational fluid dynamics solver called GT-Hybrid. Coupling of the structural/aerodynamic motion time history with the CFD analysis is done using an open File I/O process. At this writing, only a one-way coupling has been attempted, feeding the blade motion and structural deformations from OpenFAST into the fluid dynamics analysis. The sectional aerodynamic loads for a large scale 5 MW offshore wind turbine are presented, and compared against the baseline OpenFAST simulations with classical blade element-momentum theory. Encouraging agreement has been observed.
Performance and Losses Analysis for Radial Turbine Featuring a Multi-Channel Casing Design
Authors: Hassan Ahmed Farid , Schatz Markus , Vogt Damian M.
Published: January 2021

A novel control technique for radial turbines is under investigation for providing turbine performance controllability, especially in turbocharger applications. This technique is based on replacing the traditional spiral casing with a Multi-channel Casing (MC). The MC divides the turbine rotor inlet circumferentially into a certain number of channels. Opening and closing these channels controls the inlet area and, consequently, the turbine performance. The MC can be distinguished from other available control techniques in that it contains no movable parts or complicated control mechanisms. Within the casing, this difference makes it practical for a broader range of applications. In this investigation, a turbocharger featuring a turbine with MC has been tested on a hot gas test stand. The experimental test results show a reduction in the turbine operating efficiency when switching from full to partial admission. This reduction increases when reducing the admission percentage.

To ensure the best performance of the turbine featuring MC while operating at different admission configurations, it becomes crucial to investigate its internal flow field at both full and partial admission to understand the reasons for this performance reduction. A full 3D Computational Fluid Dynamics (CFD) model of the turbine was created for this investigation. It focuses on identifying the loss mechanisms associated with partial admission. Steady and unsteady simulations were performed and validated with available test data. The simulation results show that operating the turbine at partial admission results in highly disturbed flow. It also detects the places where aerodynamic losses occur and which are responsible for this performance reduction. This operation also shows flow unsteadiness even when operating at steady conditions. This unsteadiness depends mainly on the admission configuration and percentage.
Research on Damping Vibration Reduction Design Method of Aeroengine Supporting Structure System
Authors: Li Chao , Lei Binglong , Ma Yanhong , Hong Jie
Published: January 2021

Typical turbofan engine-support-structure systems having a high thrust-to-weight ratio are light, and the structure primarily comprises a plate and shells. The local vibration response of the support structure is excessively large when different frequency loads are applied. A structural vibration response control method based on dry friction damping is proposed to control the excessive vibration response. A dry friction damper with dynamic suction was designed to enhance the damping characteristics of the rotor supporting structure system in the wide frequency domain, without sacrificing the dynamic stiffness of the structure. The system is designed to effectively control the vibration response of the supporting structure at the working-speed frequency. Through theoretical modeling and simulation analyses, the influence of friction contact and damper structure characteristics on the damping effect is described quantitatively. Furthermore, the design idea and the damping process of the supporting structure are described. The calculation results show that the contact friction of the dry friction damper can consume the vibration energy of the supporting frame. A reasonable design of the contact characteristics and geometric configuration parameters of the damper can further optimize the vibration-reduction effect, and thereby improve the vibration response control design of the supporting structure system of aeroengines.
Rapid Strain Demand Estimation of Pipelines Deformed by Lateral Ground Movements
Authors: Fathi Ali , Ndubuaku Onyekachi , Yoosef-Ghodsi Nader , Hill Mike
Published: January 2021

In strain-based design and assessment, accurate measurement of pipe longitudinal strain demand is a key element in performing proper strain assessments. Quick pipeline strain assessments are usually needed after widespread natural disasters such as earthquakes or heavy rainfalls that affect multiple lines at several sites. Finite Element Analyses (FEA) and In-line Inspection (ILI) tools are the most common methods to measure/estimate the longitudinal strain demand of in-service pipelines. However, because they are rather time-consuming methods, they cannot be relied on when quick fitness-for-service evaluations of pipelines is needed. ILI needs considerable amount of time for planning and preparation as well as post-run analyses, and FEA needs extensive efforts to gather input data which might not be readily available for each site.

Enbridge recently used a method of strain demand estimation during a rapid response process to several sites affected by lateral landslides after major weather events. The method involves gathering basic field measurements of pipe deformed shape and performing analytical strain calculation by using curve-fitted deformed shape functions.

This paper describes this method, its key elements, and the assumptions on which it is based. It also presents the evaluation of this method via FEA of several pipes, soil conditions, and landslides scenarios. And finally, it concludes the capability of this method for different cases of pipes and landslides.
Time Dependent Reliability Analysis for Oil and Gas Pipelines: A Bayesian Spectral Analysis-Based Deterioration Model
Authors: Balekelayi Ngandu , Tesfamariam Solomon
Published: January 2021

Oil and gas pipelines are essential infrastructures that sustain the economy of modern society. They are designed for continuous and reliable operations over their service lives. Once installed, however, their reliability is affected by several threats among which external corrosion plays a significant role. Corrosion-based pit depth growth reduces the wall thickness over time that consequently affect the mechanical strength and the hydraulic performance of the pipeline. Pipeline utility managers rely on the corrosion growth rate models to plan their maintenance, rehabilitation and/or replacement. Existing pipeline deterioration models are mostly based on the power law function that relates the pit depth with the exposure time and rarely include the soil factors that can have effect on the corrosion growth rate. Moreover, the way these factors affect the corrosion rate is complex and cannot be captured with simple linear relationship. This paper uses data found in the literature to build a nonlinear pit depth growth model based on Bayesian spectral analysis regression technique. All continuous covariates are allowed to have smooth nonlinear spectral representations of their effect function on the pit depth growth. The discrete (i.e. categorical) factors are modeled using the ordinary least squared algorithm. The final semiparametric model allows to capture all pit depth measurements, even those difficult to be modeled using high degree polynomials. The stochastic nature of the pit depth growth is captured through the Bayesian approach. A time dependent reliability analysis using subset simulation is carried out to evaluate the changes occurring in the probability of failure of the pipe over time and allow for a better planning and management of these important infrastructure. The model is applied on a bare pipe directly exposed to the soil environment over time. The Bayesian pit depth growth model is accurate enough to allow the computation of the time dependent reliability of pipelines considering both the mechanical and hydraulic reliabilities.
Influence of Natural Gas Pipeline Explosion on Material Performance of X80 Steel Pipe Laid in One Ditch
Authors: Ling Jiatong , Dong Shaohua , Zhang Hang , Peng Donghua
Published: January 2021

Due to geographical restrictions, it is often necessary to lay two pipelines in the same ditch during pipeline construction. However, as developments in natural gas pipelines increasingly incorporate higher grades of steel, larger diameters, and higher pressures, the consequences of an accident caused by leakage, explosion, or ignition become progressively more severe. The explosion occurred in one pipe would affect the other pipe laid in the same ditch, resulting in subsequent explosion. In this study, a full-scale explosion test was conducted on two X80 steel pipes with diameters of 1422 mm and 1219 mm, laid in one ditch and set up in parallel arrangement, with a spacing of 36 m between one another, and a burying depth of 1.5 m. Some X80 steel samples were selected to assess materials performance in different areas of a given pipe in the same ditch by deploying selective explosions. The mechanical performance tests on a number of points including tensile strength, impact, and hardness were executed by the Mechanical Testing and Sensing (MTS) universal testing machine. Drop-Weight Tear Test (DWTT) of the selected samples were executed by the DWTT pendulum test machine. Metallography and microstructure analysis of the steel samples was performed by the MEF4M metallographic microscope and image analysis system. Results indicate that limited effects of jet fire on the macroscopic tensile properties and impact toughness of the pipelines, but a more obvious softening effect on the steel surface material. Drop-Weight Tear Test and microscopic observation revealed that jet fire can significantly reduce crack propagation resistance on the surface of the pipeline, pointing to deformation behavior and other concerns that could impact pipeline safety and efficacy. The results of this experimentation can help to improve pipeline construction, resulting in better safety.
Recent Progress in Development of Ductile Fracture Arrest Methodology Based on CTOA: Test Standard, Transferability and Methodology
Authors: Xu S. , Bassindale C. , Xue J. , Williams B. W. , Wang X.
Published: January 2021

Significant progress has been made in development of a new fracture arrest methodology based on a toughness parameter designed to characterize propagation — the crack-tip opening angle (CTOA). A CTOA test procedure using lab-scale DWTT-type specimens has been standardized by ASTM, and recently published experimental work has demonstrated transferability of CTOA from DWTT to full-scale pipe.

This paper will present the basic methodology for determination of CTOA using DWTT-type specimens (i.e., ASTM E3039) and other specimens such as modified double-cantilever-beam (MDCB). Recent numerical studies using cohesive zone models (CZM) and others based on damage mechanics will be discussed, including models of full-scale pipe fracture. The effects on CTOA of loading rate, specimen flattening and constraint (bending vs. tension) will be reviewed. The effect on CTOA of loading rate between quasi-static and impact (covering five orders of magnitude) is small or negligible, being within experimental scatter. Observed differences between surface and mid-thickness CTOA values will be discussed. Models of DWTT specimens using damage mechanics have shown that the CTOA for tensile loading is the same at the surface and mid-thickness and equal to the mid-thickness value for bend loading, but that the surface CTOA is significantly larger than the mid-thickness CTOA in bending. Model calculations have revealed the dependence of crack velocity on stress for a given CTOA, enabling construction of fracture resistance curves (pressure required to propagate fracture as a function of crack velocity). These first-principles curves based on CTOA can then be used in the Battelle two-curve model (BTCM) to replace empirical resistance curves based on Charpy absorbed energy (Cv). It has been known for some time that Cv over-represents the propagation resistance for high-strength high-toughness steels, requiring empirical “correction factors” to Cv in the BTCM. Experiments have shown that there is a non-linear correlation between Cv and CTOA, explaining the need for correction factors to Cv and supporting the use of CTOA as a more appropriate propagation toughness.
Analysis of the Mechanical Behaviors of Fiber Reinforced Unbonded Flexible Pipe Under Combined Load
Authors: Wang Baodong , Zhang Hong , Liu Xiaoben , Xu Lixin , Fu Yang
Published: January 2021

Unbonded flexible pipe is widely used in the oil and gas industry for its good flexibility, especially in deepwater oil and gas transportation. And the fiber reinforced unbonded flexible pipe has excellent corrosion resistance and wear resistance. However, they are subjected to internal pressure, external pressure and tensile loads during the service process, which are important factors affecting the integrity and security of the flexible pipe. In this paper, the mechanical behaviors of an 8-inchs fiber reinforced unbonded flexible pipe used in offshore gas development which consists of internal layer, internal pressure reinforcement layers, anti-wear layers, external pressure armor, tensile reinforcement layers and outer sheath is investigated by numerical methods. A rigorous three-dimensional solid finite element model of flexible pipe that considers the real material parameters, structural nonlinearity as well as the nonlinear contact behavior was created. ABAQUS/Explicit quasi-static simulation is adopted to study the mechanical behaviors of the flexible pipe under combined load. And the accuracy of the simulation method for the fiber reinforced layers such as internal pressure layer is verified by comparing with the small-scale internal pressure burst test of 1-inch flexible pipe. The mechanical behavior of flexible pipe subjected to internal pressure, external pressure and tensile load was investigated in detail. Based on the contrastive analysis, some practical conclusions have been obtained which may be used for the practical design and production of flexible pipe. This study can be referenced for the applications of unbonded flexible pipe in marine oil and gas production.