bluuebunny/crossref_metadata_2025_split huggingface dataset:
Some Observations on the Computational Sensitivity of Rotating Cavity Flows
Authors: Hickling Tom , He Li 
Published: January 2021

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.