bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Surface Tension on Bubble Generation in Gas-Sheared Liquid Films
Authors: Vasques João , Ibrahim Abubakr , Hann David , Simmons Kathy , Walsh Michael 
Published: November 2019

Abstract
In the bearings of an aero-engine, oil is supplied not only for lubrication, but mostly for cooling, where heat is removed from the hot walls of the chambers by the oil films that are formed there. Based on prior work, it is observed that air bubbles can become trapped within liquid films potentially affecting fluid behavior.
This paper reports on experiments conducted in a horizontal rectangular duct, where the liquid phase was sheared by a strong gas stream. In this configuration, air bubbles are seen to be entrapped in a similar manner to what was observed within prior bearing chamber visualization research. Of particular interest in this paper, is the effect of surface tension on air bubble generation in the liquid phase and its consequences for appropriate oil selection criteria. The surface tension was controlled by testing solutions with reduced surface tension by up to 47% of that of water, while maintaining the density and viscosity parameters constant. The results were obtained using a Brightness-Based Laser-Induced Fluorescence technique.
Results show that reducing surface tension leads to a higher number of bubbles being generated, thus increasing the level of aeration of the liquid phase. Additionally, the velocity of the bubbles was also measured and seen to be lower for the lower surface tension cases.
Accuracy Assessment of Steady and Unsteady Multistage High Pressure Compressor Simulations
Authors: Lück Sebastian , Kuntzagk Stefan , Doebbener Guido , Kellersmann Andreas , Bode Christoph , Friedrichs Jens 
Published: November 2019

Abstract
In this paper a comparison of the performance parameters and flow characteristics of a mature commercial high bypass engine’s 9-stages high pressure compressor (HPC) with steady-state mixing-plane (RANS) and unsteady RANS (URANS) CFD is carried out. The investigation is based on a numerical model of the CFM56-5C engine’s HPC which is installed on the Airbus A340-300 aircraft. The compressor under investigation features the so called 3D blading which is the first of two performance improvement packages available. An experimental engine of this type equipped with extensive additional instrumentation is in use by Lufthansa Technik to deliver detailed experimental data of the gas path. Experimental results have been discussed in previous works of the authors.
In order to provide long-term forecasts of an engine’s state the aforementioned CFD model has been included into a multilevel engine model.
To be able to evaluate the significance and applicability of the CFD results into such model, it is of great interest to which extent and level of detail it can deliver accurate performance predictions.
From the comparison of both steady-state and unsteady simulation results it is found that overall compressor performance only differs negligibly while stage performance can differ significantly. It is depicted that among the stator vanes of the front stages local supersonic flow and flow separation can occur. These are not captured by the steady-state simulation to the same degree a time resolved simulation does. In rear stages differences fade and unsteady methods tend to predict better stage performance which may be due to favourable effects of rotor-stator interaction.
Comparison of Machine Learning Algorithms in the Interpolation and Extrapolation of Flame Describing Functions
Authors: McCartney Michael , Haeringer Matthias , Polifke Wolfgang 
Published: November 2019

Abstract
This paper examines and compares commonly used Machine Learning algorithms in their performance in interpolation and extrapolation of FDFs, based on experimental and simulation data. Algorithm performance is evaluated by interpolating and extrapolating FDFs and then the impact of errors on the limit cycle amplitudes are evaluated using the xFDF framework. The best algorithms in interpolation and extrapolation were found to be the widely used cubic spline interpolation, as well as the Gaussian Processes regressor. The data itself was found to be an important factor in defining the predictive performance of a model, therefore a method of optimally selecting data points at test time using Gaussian Processes was demonstrated. The aim of this is to allow a minimal amount of data points to be collected while still providing enough information to model the FDF accurately. The extrapolation performance was shown to decay very quickly with distance from the domain and so emphasis should be put on selecting measurement points in order to expand the covered domain. Gaussian Processes also give an indication of confidence on its predictions and is used to carry out uncertainty quantification, in order to understand model sensitivities. This was demonstrated through application to the xFDF framework.
An Inverse Approach to Identify Tuned Aerodynamic Damping, System Frequencies and Mistuning: Part 3 — Application to Engine Data
Authors: Figaschewsky Felix , Kühhorn Arnold , Beirow Bernd , Giersch Thomas , Schrape Sven , Nipkau Jens 
Published: November 2019

Abstract
A novel approach for the identification of tuned aerodynamic damping, system frequencies, forcing and mistuning has been introduced in the first part of this paper. It is based on the forced response equations of motion for a blade dominated mode family. A least squares formulation allows to identify the system’s parameters directly from measured frequency response functions (FRFs) of all blades recorded during a sweep through a resonance. The second part has dealt with its modification and application to experimental modal analyses of blisks at rest.
This 3rd part aims at presenting the application of the approach to blade tip timing (BTT) data acquired in rig tests. Therefore, blisk rotors of two different engines are studied: a single stage fan rig and a 4.5 stage high pressure compressor (HPC) rig. The rig test campaign of the fan blisk included also an intentional mistuning experiment that allows to study the performance of the identification approach for a similar rotor with two different mistuning levels. It is demonstrated that the approach can identify aerodynamic damping curves, system frequencies, mistuning pattern and forced travelling wave modes (TWMs) from state of the art BTT data monitored during rig or engine tests. All derived mistuning patterns could be verified with reference measurements at standstill. The derived aerodynamic damping curves and system frequencies show a reasonable agreement with simulations. For the HPC case a multitude of excited TWMs could be identified which also lines up with previous simulations.
An Overview of Initial Operational Experience With the Closed-Loop sCO2 Test Facility at Cranfield University
Authors: Anselmi Eduardo , Bunce Ian , Pachidis Vassilios 
Published: November 2019

Abstract
An experimental facility is currently operating at Cranfield University in the UK and it is being used to explore supercritical carbon dioxide as a working fluid for future bottoming power cycle applications. The initial objective of this experimental programme is to de-risk and demonstrate the robustness of a closed-loop system, whilst proving the function and performance of individual components and various measurement and control modules. This paper describes the first operational experience gained whilst operating the test facility. More specifically, it summarizes the lessons learned from the commissioning phase and first test campaigns carried out in 2018.
Transient Thermodynamic Modeling of Air Cooler in Supercritical CO2 Brayton Cycle for Solar Molten Salt Application
Authors: Deshmukh Ankur , Kapat Jayanta , Khadse Akshay 
Published: November 2019

Abstract
Supercritical CO2 Brayton power cycle is getting commercially attractive for power generation due to its numerous advantages like zero water discharge, compactness, low environmental emission and potential to reach high thermal efficiency at lower costs. A typical recuperated sCO2 closed cycle consists of three heat exchangers (main heat exchanger, cooler and recuperator) and two turbomachinery (sCO2 turbine and sCO2 compressor). The cooler which can use air or water as heat sink is the focus of this study. The purpose of the paper is investigation of behavior of thermodynamic parameters of cooler during transient operations. In this study, dynamic simulation is performed to analyze the transient behavior of air cooler in sCO2 cycle using molten salt as heat source from solar energy. Transient study is critical to understand the thermodynamic behavior of each system with time. Rapid changes in ambient temperature, operating loads, start-ups and shutdowns affect the performance of the turbomachinery and heat exchangers. The change in the thermal performance of air cooler with the change in boundary conditions is demonstrated here. The simulation is setup by having a steady state design of 100MWe sCO2 cycle with operating temperature of 700°C and pressure of 250 barA. Dynamic calculations are done using LMS AMESim. Transients studied in this paper include (i) step variation (ii) standard variation (iii) linear variation of air temperature. This work thus serves as a framework to develop a design basis for sCO2 cycle components as a function of transient operating conditions.
Application Concepts and Experimental Validation of Constitutive Material Models for Creep-Fatigue Assessment of Components
Authors: Kontermann Christian , Linn Stefan , Oechsner Matthias 
Published: November 2019

Abstract
The possibility to use real operational data as an input for lifetime assessment methods is a key requirement in terms of both service applications as well as within the design of components by underlying specific service relevant scenarios. To address this, so called “Constitutive Viscoplastic Material Models” have been developed which represent a more generalized alternative for assessing turbo machinery components which undergo an irregular creep-fatigue loading.
Based on several experimental and theory related national research programs, performed within the German working group W10 in the last years, the current status of the model development and the performance potentials are summarized in this paper. Within the first part, the general and developed model structure of one candidate material model is introduced by discussing different aspects of the equation system together with the specific practical related aspects. Secondly, the validation of this constitutive material model is shown by comparing the model results with a set of conducted complex experiments, like ansiothermal service like experiments performed on smooth, notched and biaxially loaded cruciform test samples. As the third focus, the applicability and the potential of using such a model for assessing real components will be discussed e.g. by introducing extrapolation or cycle jump concepts which allows to majorly reduce the calculation time without decreasing the result accuracy significantly. Finally, future potentials will be introduced with the goal to use such sophisticated models to train meta-models and finally allow for a machine-learning based on-site and service related on-line component assessment.
Assessment of Thermo-Electric Power Plants for Rotorcraft Application
Authors: Roumeliotis Ioannis , Mourouzidis Christos , Zafferetti Mirko , Pachidis Vassilios , Broca Olivier , Unlu Deniz 
Published: November 2019

Abstract
This paper assesses a parallel electric hybrid propulsion system utilizing simple and recuperated cycle gas turbine configurations. An adapted engine model capable to reproduce a turboshaft engine steady state and transient operation is built in Simcenter Amesim and used as a baseline for a recuperated engine. The transient operation of the recuperated engine is assessed for different values of heat exchanger effectiveness, quantifying the engine lag and the surge margin reduction which are results of the heat exchanger addition.
An oil and gas mission of a twin engine medium helicopter has been used for assessing the parallel hybrid configuration. The thermo-electric system brings a certain level of flexibility allowing for better engine utilization, thus firstly a hybrid configuration based on simple cycle gas turbine scaled down from the baseline engine is assessed in terms of performance and weight. Following the recuperated engine thermo-electric power plant is assessed and the performance enhancement is compared against the simple cycle conventional and hybrid configurations.
The results indicate that a recuperated gas turbine based thermo–electric power plant may provide significant fuel economy despite the increased weight. At the same time the electric power train can be used to compensate for the reduced specific power and potentially for the throttle response change due to the heat exchanger addition.
Numerical Performance Assessment of a Turbine Blade Row Operating Under Pulsed Detonation Combustion Inlet Conditions
Authors: Cuciumita Cleopatra , Paschereit Christian Oliver 
Published: November 2019

Abstract
Pulsed detonation combustion is not a new research topic. However, since the detonation process was first observed in 1881, the interest in it grew substantially in the last decades. Because the gas turbines have reached their technological maturity, the scientific community has started looking into novel thermodynamic cycles, such as detonation-based cycles. Numerous studies have been recently published in the field of pulsed detonation combustion, both numerical and experimental and major breakthroughs have been achieved in understanding and controlling the phenomena. However, the topic remains of mostly academic interest, one of the reasons is that practical implementation of it is reliant turbomachinery that would efficiently convert the pulsed, high peak, pressure into useful work. The few studies conducted on classical, existing turbines, show an efficiency of around 50% when coupled with a PDC. The low efficiency has been directly connected with the shock wave losses. For this reason, the design of turbines with supersonic inlet, and associated performance assessments have been researched. This work, however, has supersonic steady inlet Mach number or sinusoidal pulsating conditions around an average subsonic value. No public literature exists on the performances of turbines operating at pulsating inlet conditions similar to the outlet of a PDC. The current paper tackles exactly this issue. The geometry for a turbine stator row was designed based on supersonic inlet design criteria. This geometry was then subjected to CFD numerical simulations. First, the pressure losses associated with a constant supersonic inlet were numerically determined to be a little over 26%. The next step was to assess the pressure losses of the same turbine row geometry in a transient approach. This time, the inlet conditions were set to be variable in time. The values were taken from a 1D in-house code computing the parameters at the outlet of a PDC working on hydrogen and air under stoichiometric conditions. This inlet conditions give a much better insight with respect to the flow within a turbine row when coupled with a PDC. It was observed that the pressure losses, computed as a time average for a period corresponding to the PDC functioning frequency were of 12%. This value is much less than that for a constant supersonic inlet, mostly due to the turbine being exposed to the shock waves for less time.
Selecting the Optimum Supercritical CO2 Cycle for Indirect-Fired Applications
Authors: Tom Brittany , Smith January , McClung Aaron M. 
Published: November 2019

Abstract
Existing research has demonstrated the viability of supercritical carbon dioxide as an efficient working fluid with numerous advantages over steam in power cycle applications. Selecting the appropriate power cycle configuration for a given application depends on expected operating conditions and performance goals. This paper presents a comparison for three indirect fired sCO2 cycles: recompression closed Brayton cycle, dual loop cascaded cycle, and partial condensation cycle. Each cycle was modeled in NPSS with an air side heater, given the same baseline assumptions and optimized over a range of conditions. Additionally, limitations on the heater system are discussed.
Acoustic and Convective Mechanisms Contributing to Non-Synchronous-Vibrations in a Multistage Compressor
Authors: Brandstetter Christoph , Paoletti Benoit , Ottavy Xavier 
Published: November 2019

Abstract
In the present paper we show an analysis of Non-Synchronous-Oscillations in the rear stage of an experimental high-speed 3.5 stage compressor. The machine CREATE is representative of the rear median-stages of a modern civil turbofan engine except for an increased tip clearance on middle and last stage. Using distributed unsteady pressure measurements a comprehensive dataset during transient throttling maneuvers is presented, including temporal and spatial mode decomposition and the derivation of wave propagation speeds. To support the aerodynamic characterization, the steady flow structure at near stall conditions has been investigated using Laser-Doppler-Anemometry and unsteady pressure probes. In repeated experiments the machine has encountered alternating circumferential modes, several hundred revolutions before rotating stall at design speed. It was found that acoustic resonance of an upstream cut-on mode between the compressor stages enforces the development of particular modes. These phenomena have not been observed on the same machine with regular tip clearance. In contrast to front-stage observations reported in literature, where leading edge separations cause strong excitations of the blade eigenmodes, initially weak modulations of the flow in the rotor tip region are observed to be amplified due to acoustic feedback. With rising amplitude lock-in to distinct circumferential mode orders develops. Apart from the final lock-in procedure, signatures of solely aerodynamic fluctuations, discussed in literature as ‘Rotating Instabilities’ or ‘Part Span Stall’, are observed intermittently at different speedlines.
Nonlinear Aerodynamic Damping in a Highly Loaded Vibrating Compressor Cascade
Authors: Schuff Matthias , Chenaux Virginie 
Published: November 2019

Abstract
A numerical aeroelastic study of a 2D linear compressor cascade based on the non-rotating annular compressor cascade with a NACA3506 profile was performed using a one-way coupled technique (prescribed-motion approach). Subsonic and transonic flow conditions with strong shocks in the blade passage were imposed. Using a nonlinear harmonic balance solver, unsteady simulations were performed by enforcing one blade oscillation motion. For each blade structural mode, the blade deflection amplitude was varied and its influence on the blade aerodynamic response was determined in terms of aerodynamic damping. The blade modes investigated consisted of one pitching and two heaving oscillation motion. In transonic flows and for the three structural modes investigated, the cascade shows nonlinear aerodynamic responses depending on the vibration amplitude. The results presented in this work show that nonlinear frequency domain methods are able to capture the blade nonlinear aeroelastic behavior coming from amplitude-dependent aerodynamic responses.
Comprehensive Smith Charts for Axial Compressor Design
Authors: Anderson Mark R. 
Published: November 2019

Abstract
The “Smith Chart” has been recognized as an indispensable technique when applied to the initial design of axial compressors and turbines. The Smith Chart offers a simple method to locate the region of optimum efficiency which is achievable as a function of flow and work coefficient. The result is a targeted flow state represented by the velocity triangles that result from these coefficients.
The process was originally developed, and is best documented, for axial turbines1. Over the years, several publications, of similar methods for axial compressors have been put forward. The author presented one such work2 which made significant use of optimization to develop an improved Smith chart for moderate Mach number compressor designs. In the current work, these results are expanded to both low Mach number (basically incompressible) to high-speed transonic cases as well. Similar to the previous work, the effort makes extensive use of optimization to systematically explore the optimum 2D profile shapes for a wide range of target flow and work coefficients. The method uses an FNS quasi-3D CFD solver, coupled to an efficiently parameterized geometry generator, combined with an automated optimization process. The process was applied independently to dozens of flow and work coefficient points to generate comprehensive maps of performance.
Results are shown for three different relative inflow Mach numbers: 0.2, 0.75, and 1.1. The maps are displayed in classic Smith chart format of islands of stage efficiency as a function of the flow and work coefficient. Specifically, the results are for axial compressor stages of 50% reaction, the theoretical ideal reaction for 2D flow. The results and the implications over varying Mach numbers are discussed. Also included is an expanded discussion of the range and accuracy of various meanline modeling methods, along with their ability to determine the optimum design condition.
Digital Solutions for Power Plant Operators in a Dynamic Market Place: An Advanced Automated Gas Turbine Combustion Tuning for Low Emissions and Operational Flexibility
Authors: Demougeot Nicolas , Steinbrenner Alexander , Wang Wenping , Yaquinto Matt 
Published: November 2019

Abstract
Since the advent of premix combustion technology in industrial gas turbines, regular manual combustion tuning and engine adjustments have been necessary to maintain engines within emission regulatory limits and to control combustion dynamics (pulsations) for hardware integrity. The emissions and pulsation signatures of premix combustors are strongly driven by ambient conditions, engine performance, degradation and fuel composition. As emissions limits became more stringent over the years, higher combustion dynamics were encountered and challenges to maintain acceptable settings after yearly combustion inspections were regularly encountered. This challenge was further increased as sites operating advanced Gas Turbines (GT) eliminated Combustion Inspections (CI) and required uninterrupted generation at optimum settings for up to three years. The case for automated tuning systems became evident for the Industrial Gas Turbine (IGT) market in the mid 2000’s and different IGT manufacturers and service providers began developing them. Power Systems Manufacturing (PSM) developed the AutoTune (AT) system in 2008 and has since installed it in over fifty units, accumulating close to a million hours of operation. The history of PSM’s AT system development as well as a description of its fundamental principles and capabilities are discussed.
The power generation market is changing rapidly with the injection of renewables, thus driving the demand for operational flexibility, the design of PSM’s multi-platform compatible, AutoTune system; allowing for increased peak power, extended turndown and transient tuning is discussed. The paper also describes, how, using the same tuning principles, the application for an AutoTune system can be extended to the Balance Of Plant (BOP) equipment.