bluuebunny/crossref_metadata_2025_split huggingface dataset:
Loop Filling and Start Up With a Closed Loop sCO2 Brayton Cycle
Authors: Cich Stefan D. , Moore J. Jeffrey , Day Towler Meera , Mortzheim Jason , Hofer Douglas 
Published: November 2019

Abstract
Recent testing has been performed on a 1 MWe sCO2 closed loop recuperated cycle under funding from the US DOE Sunshot initiative and industry partners. Some of the goals of this funding included the development of a 1 MWe loop, a 10 MWe turbine, and performance and mechanical testing. One of the key challenges that presented itself was the filling, start-up, and shut down of the entire system. Understanding the loop transient performance is important when having to bring a turbine online, transitioning from peak to partial loading, and also managing routine and emergency shut downs. Due to large changes in density near the critical point for CO2 and its tendency to form dry ice when expanded to atmospheric pressure, managing loop filling and venting is critical in ensuring that components do not get damaged. Specific challenges were centered on protecting the dry gas seals, maintaining proper mass in the loop, and also thermal transients during trips. This paper will take a detailed look at the challenges encountered during start up and shut downs, and also the solutions that were implemented to successful transition between different phases of the testing.
Verification of Combined Main Steam Valve Pressure Distribution and Vibration Characteristics With Downscale Model Test on Air Condition
Authors: Suzuki Fumiyuki , Nishida Shingo , Fukao Shinji , Tsuruta Megumu 
Published: November 2019

Abstract
In order to enhance the efficiency and reduce the manufacturing cost of steam turbine, combined main steam valve consisting of main stop valve and control valve in the same casing has been developed. Combined main steam valve with improved flow path at internal structure will reduce pressure loss. A downscale model test on air condition was conducted to verify pressure distribution characteristics. Experimental result and numerical result obtained by computational fluid dynamics (CFD) showed reasonable agreement in pressure loss and static pressure at each flow point within the design operation range. Main stop valve (SV) and control valve (CV) vibration characteristics tests were performed simultaneously for the stability verification of governing operation from start up to full load. We confirmed that CV aerodynamic added damping ratio was positive under all measured condition of CV stroke and pressure ratio, and self-excited vibration was not generated. We also confirmed that pressure fluctuation acting on main stop valve body was sufficiently small within the operation range. Meanwhile, in the case where pressure ratio or CV stroke deviated from the operation range, pressure fluctuation around main stop valve increased. Based on CFD result and detailed analysis of experimental result, it was found that steam flow along valve seat separates periodically, which revealed the mechanism of increasing pressure fluctuation around main stop valve. By reflecting on these results, the reliability of new combined main steam valve has substantially been enhanced.
Limiting Inlet Conditions for Phase Change Avoidance in Supercritical CO2 Compressors
Authors: Allison Timothy C. , McClung Aaron 
Published: November 2019

Abstract
In many supercritical CO2 cycle implementations, compressor or pump inlet conditions are relatively near the two-phase region. Fluid acceleration near the compressor inlet can result in the potential for condensation or cavitation at the inlet. Despite potential mitigating effects or evidence in the literature, potential two-phase operation is a high-risk condition and may not be recommended for high-reliability system design. This paper presents a summary of the existing literature documenting inlet phase change in sCO2, and presents an analysis of required conditions to avoid phase change as a function of inlet pressure, temperature, and Mach number. Static conditions at the inlet are calculated based on the real gas approach documented in ASME PTC-10, Appendix G. In addition, various total-to-static iteration challenges are discussed and avoided through solution of the inverse problem to convert limiting static conditions at saturation to the full range of limiting total conditions for various Mach numbers up to 1.0. The results show that a threshold total temperature exists above which phase change cannot occur, ranging from 31.1 to 66.95 °C and increasing with Mach number. Lower temperatures below this threshold may also avoid phase change depending on the total pressure. The documented results are useful as a reference for use by cycle designers to impose design limits that minimize risks associated with two-phase flow in the compressor.
Flow Mechanism and Loss Analysis of Tip Leakage Flow With Delayed Detached Eddy Simulation
Authors: Li Hui , Bian Xiutao , Su Xinrong , Yuan Xin 
Published: November 2019

Abstract
The complex leakage flow structure in the tip region of unshrouded rotor is a main source of turbine aerodynamic loss. Due to the complex turbulence characteristics of the tip leakage flow, the widely used Reynolds Averaged Navier-Stokes (RANS) approach may fail to accurately predict the multi-scale turbulent flow and the related loss. In order to effectively improve the turbine efficiency, more insights into the turbulence characteristics and the loss mechanism in the tip leakage flow are required. In this work, a Delayed Detached Eddy Simulation (DDES) study is conducted to simulate the flow inside a high pressure turbine blade, with emphasis on the tip region. DDES results are in good agreement with the experiment and the comparison with RANS results verifies the advantages of DDES in resolving finer flow structures of leakage flow, also in capturing the complex turbulence characteristics. The snapshot Proper Orthogonal Decomposition (POD) method is used to extract the dominant flow features. The flow structures and the distribution of Reynolds stress help to reveal the process of leakage flow and its interaction with the secondary flow. Meanwhile, it is found that the separation vortex (SV) forms from leading edge to trailing edge, and the strong interactions between tip leakage vortex (TLV) and passage secondary vortex (PSV) significantly enhance the turbulence intensity. Based on the DDES results, loss analysis of tip leakage flow is conducted based on entropy generation rates. For the leakage flow related loss, the largest local entropy generation rate occurs at 50 % of axial chord, and the interaction between the leakage vortex and up passage vortex promotes the loss generation. To sum up, the current DDES study about the tip leakage flow provides helpful information about the loss generation mechanism and may guide the design of low-loss blade tip.
Experimental Investigation on Real Under-Platform Dampers: The Impact of Design and Manufacturing
Authors: Gastaldi Chiara , Berruti Teresa M. , Gola Muzio M. , Bessone Andrea 
Published: November 2019

Abstract
The focus of this paper is on underplatform dampers (UDPs), friction damping devices commonly used in turbines for power generation. Given the nonlinear and highly complex nature of dry friction, model validation of bladed disks with UPDs still relies heavily on experimental verification, which is typically performed using the Frequency Response Function. The AERMEC research group has, in the last ten years, promoted an additional experimental/numerical comparison, based on evidence gathered directly at the blade platform/UPD interface to increase the understanding of friction and damper mechanics. A new test rig for the direct experimental investigation of UPDs at frequencies and contact pressures in line with real working condition has been developed. The geometry of the test rig and its technical features are described in detail in the paper.
Different real dampers (real shape and material) are tested. The results analysis includes a complete understanding of the contact states undergone by each damper during a period of vibration and an estimation of its contact parameters. The influence of the damper shape together with the precision of the surface manufacturing and finishing on the damper effectiveness is addressed.
Rotordynamic Stability Evaluation With Constructed Forward Whirl Signals Based on Full Spectrum Technique: Numerical and Experimental Investigation
Authors: Li Qihang , Chu Fulei 
Published: November 2019

Abstract
The rotordynamic stability evaluation by measuring the damping ratio or log-dec of the first forward whirl mode in the shop test is of importance to reduce the risk of instability fault in field. This paper focuses on the signal processing of inverse Fourier transform based on the full spectrum technique to reduce the modal overlap of closely-spaced first order modes (in which the amplitudes of the forward and backward responses are comparable) in the time domain. By using this transform method, forward and backward whirl signals are obtained, and blocking excitations in x or y direction can also achieve the same effectiveness as the forward and backward excitation with the active magnetic bearing (AMB) when there is a significant cross-coupled stiffness (CCS). The envelope of the analytical signal obtained by Hilbert transform is used to analyze the component of the excited vibration and show the effectiveness of weakening the overlap of the closely-spaced twin modes. The result from the numerical investigation indicates that for the rotor-bearing system with a significant CCS, the constructed forward and backward whirl signals are clearly dominated by the respective forward and backward modes with no significant overlap. Besides, experiments are also carried out in a nearly industrial centrifugal compressor test rotor with AMB, which is used as an actuator to apply blocking excitations for rotordynamic stability tests, with result that the unidirectional excitation is enough to estimate the log-dec of the rotor system with a slight CCS. Thus, the traditional circular forward/backward whirl excitation and its associated complicated equipment such as AMB is unnecessary and replaceable, providing a sight to simplify the complicated equipment only by using the signal processing techniques when the rotating machinery has an either slight or significant CCS.
Effects of Jetting Orifice Geometry Parameters and Channel Reynolds Number on Bended Channel Cooling for a Novel Internal Cooling Structure
Authors: He Wei , Deng Qinghua , He Juan , Gao Tieyu , Feng Zhenping 
Published: November 2019

Abstract
A novel internal cooling structure has been raised recently to enhance internal cooling effectiveness and reduce coolant requirement without using film cooling. This study mainly focuses on verifying the actual cooling performance of the structure and investigating the heat transfer mechanism of the leading edge part of the structure, named bended channel cooling. The cooling performances of the first stage of GE-E3 turbine with three different blade leading edge cooling structures (impingement cooling, swirl cooling and bended channel cooling) were simulated using the conjugate heat transfer method. Furthermore, the effects of jetting orifice geometry and channel Reynolds number were studied with simplified models to illustrate the flow and heat transfer characteristics of the bended channel cooling.
The results show that the novel internal cooling structure has obvious advantages on the blade leading edge and suction side under operating condition. The vortex core structure in the bended channel depends on orifice width, but not channel Reynolds number. With the ratio of orifice width to outer wall thickness smaller than a critical value of 0.5, the coolant flows along the external surface of the channel in the pattern of “inner film cooling”, which is pushed by centrifugal force and minimizes the mixing with spent cooling air. Namely, the greatly organized coolant flow generates higher cooling effectiveness and lower coolant demand. Both the Nusselt number on the channel surfaces and total pressure loss increase significantly when the orifice width falls or channel Reynolds increases, but the wall jet impingement distance appears to be less influential.
Transient CFD Co-Simulation of a 3D Compressor Model in its 1D System Environment
Authors: Spille-Kohoff Andreas , Hetze Farai , Du Toit Bennie 
Published: November 2019

Abstract
Rotary compressors such as screw compressors, roots blowers, and turbo compressors are used in industry to compress process gases, or as vacuum or backing pumps to evacuate vessels. Gas is sucked in at low-pressure side, transported and compressed by size-changing chambers (PD machines) or energy transmission from rotor to fluid (turbo machinery), and released at high-pressure side. In expanders or turbines, flow direction is from high to low pressure side to gain energy from pressurized gases. The 3D CFD simulation of such compressors/expanders is complex and time-consuming due to its transient nature and fine meshes to ensure a proper representation of radial and axial gaps in the range of some microns with machine dimensions up to meters. Due to this complexity, 3D CFD simulation should focus on the component, i.e. the compressor, and the attached overall system with vessels, valves, pipes, and consumers should be simulated in a 1D network or system simulation. Due to oscillations in the gas flow and interaction with the connected system a transient coupling is necessary. In this paper we show a 3D CFD simulation of a screw compressor using ANSYS CFX in a co-simulation with the 1D Flownex simulation environment of a network modelling the pressurized gas distribution. Whereas the 3D solver works on meshes with up to several million nodes in parallel on HPC systems, the 1D solver typically works serially on several thousand nodes that discretize the flow direction. The transient coupling is based on the exchange of variables at the boundaries of each simulation for every time step allowing for detailed analysis. The impact of the acoustic propagation of pressure fluctuations and the pulsating fluid flow provided by the compressor on the distribution system, and in return the effects of the system response on the compressor are evaluated. Furthermore transient scenarios such as start-up procedures or component failure will be shown.
Prediction of the Flow Response of a Turbulent Flame to Acoustic Pertubations Based on Mean Flow Resolvent Analysis
Authors: Kaiser Thomas Ludwig , Lesshafft Lutz , Oberleithner Kilian 
Published: November 2019

Abstract
Resolvent analysis is applied to a non-reacting and a reacting swirled jet flow. Time-averaged flows as input for the resolvent analysis and validation for the results of the resolvent analysis are obtained by experiments. We show that in the non-reacting (cold) flow case, the resolvent analysis is capable of predicting the hydrodynamic response to upstream harmonic acoustic forcing if the flow shows low-rank behavior. This is the case for low and moderate acoustic forcing amplitudes. Even for very strong acoustic velocity amplitudes, that are of the same order of magnitude as the flow velocity, the resolvent analysis still provides reasonable results. The method also yields very good results for the reacting flow in terms of velocity fluctuation and heat release response to the acoustic forcing. This confirms the idea that the resolvent method could be applied to estimate the Flame Transfer Function based on the mean flow and flame.
Influence of Lubrication Oil on the Performance of Carbon Fibre Brush Seals for Aero-Engines Bearing Chambers
Authors: Outirba Bilal , Hendrick Patrick 
Published: November 2019

Abstract
Carbon fibre brush seals are an alternative to labyrinth seals in aero-engines lubrication systems due to better sealing ability with low power loss. However, the use of brush seals still raises concerns about coking issues. In addition, the influence of oil on the brush seal behaviour needs to be fully assessed. This paper provides an experimental investigation of the effect of lubrication oil on the performance of carbon fibre brush seals under static and dynamic conditions. Eight brush seal samples of various geometrical designs were submitted to an environment recreating the working conditions of a modern aero-engine bearing chamber in terms of rotational speed, air pressure, and oil type of injection and temperature. The test results indicated that the performance of carbon fibre brush seals was deeply influenced by the presence of oil within fibres. Oil deeply influences leakage performance, depending on geometrical parameters (density, fibre length and interference) and operating conditions (oil temperature, rotational speed). Brush seal fibre pack is mainly prone to hydrodynamic lift and oil soaking, which is defined by the ability of lubrication oil to fill in properly the interstices between fibres. Viscosity and surface tension may be the key properties influencing oil soaking. Seal torque data corroborates the presence of a hydrodynamic lift. In addition, in absence of differential pressure, seal torque decrease with when oil temperature increases indicates the existence of a critical viscosity. Finally, oil lubrication within the bristles allows reduction of the inter-bristle friction, thus limiting hysteresis.
Modelling and Design of LPC Components With Semi-Analytical Models: Part I — Model Formulation and Validation
Authors: di Mare Luca , Carnevale Mauro , Rife Max E. , Kulkarni Davendu , Northall Richard 
Published: November 2019

Abstract
The adoption of very high bypass ratios is an effective strategy to improve the performance of turbofans for civil aviation. Very high-bypass ratio turbofans are characterized by large-diameter fans and large intake diameters, whereas the overall length of the engine and its installation have to be contained to prevent excessive weight growth. As a result, the main components of the low-pressure compression system (LPC) are closer to each other in modern and future engines than they were in less recent designs, if distances are measured in terms of engine diameter. As the axial decay of potential distortions takes place over distances comparable to their tangential wavelength, modern and future engines also display stronger interactions between the intake, the fan, the OGVs and the pylons, causing performance and integrity issues that need to be addressed at the design stage.
The direct computation of whole LPC systems through CFD is expensive on account of the large extent of the domain and the wide range of wavelengths/frequencies that need to be resolved. This makes CFD unsuitable for bypass design. However, as the interaction between intake, fan, OGV and bypass takes place mainly through flow potential over long wavelengths, drastic simplifications can be introduced. Correspondingly, considerable computational savings are possible by resorting to semi-analytical models.
In this Part I of a two-part paper, a model for the intake/fan/OGV bypass interaction problem based on potential flow is presented. The model can describe the potential component of the LPC flow field, as well as vorticity distortions transmitted through the fan and those generated by the fan as a result of the non-uniform work done around the circumference. The method is validated against CFD results on a configuration typical of modern machines for civil aviation service and is demonstrated as a useful preliminary design tool.
Off-Design Performance Evaluation of a LNG Production Plant Coupled With Renewables
Authors: Ancona M. A. , Bianchi M. , Branchini L. , Catena F. , De Pascale A. , Melino F. , Peretto A. 
Published: November 2019

Abstract
In the last years, the increased demand of the energy market has led to the increasing penetration of renewable energies, in order to achieve the primary energy supply. Simultaneously, natural gas is predicted to play a vital and strategic role in the energy market, on account of its lower environmental impact than other fossil fuels, both as gaseous fuel for stationary energy generation and as liquefied fuel. In particular, the Liquefied Natural Gas (LNG) is becoming interesting in transports as an alternative to diesel fuel, allowing a decrease in pollutant emissions and a reduction in fuel’s costs for the users. As a consequence, in this context, the LNG production process can be seen as an electrical storage system by the integration with renewables, becoming an interesting solution to avoid the issues related to intermittency and unpredictability of renewables.
The aim of the paper is the development of a calculation code and the evaluation of the off-design operation of a LNG production plant coupled with wind renewable energy sources. With this purpose, on the basis of mathematical models from literature, a dedicated calculation code has been developed, able to thermodynamically analyze both design and off-design operation of the integrated process. In addition, in this study the proposed model is employed to investigate the correct integration between renewables and LNG generation, in order to define the optimal choice of the wind size for a given LNG production plant. With this purpose, the LNG plant size of a real prototype has been considered and an economic analysis has been carried out, accounting for the revenue of the LNG sale, the costs for NG purchase, for operation and maintenance and for the initial investment costs, but also with the aim to minimize the electricity introduction into the grid, considered in this study as a penalty.
Numerical Simulation of Non-Equilibrium Condensation in Supercritical CO2 Compressors
Authors: Brinckman Kevin W. , Hosangadi Ashvin , Liu Zisen , Weathers Timothy 
Published: November 2019

Abstract
There is increasing interest in supercritical CO2 processes, such as Carbon Capture and Storage, and electric power production, which require compressors to pressurize CO2 above the critical point. For supercritical compressor operation close to the critical point there is a concern that the working fluid could cross into the subcritical regime which could lead to issues with compressor performance if condensation was to occur in regions where the fluid dropped below the saturation point. Presently, the question of whether there is sufficient residence time at subcritical conditions for condensation onset in supercritical CO2 compressors is an unresolved issue. A methodology is presented towards providing a validated simulation capability for predicting condensation in supercritical CO2 compressors. The modeling framework involves the solution of a discrete droplet phase coupled to the continuum gas phase to track droplet nucleation and growth. The model is implemented in the CRUNCH CFD® Computational Fluid Dynamics code that has been extensively validated for simulation at near critical conditions with a real fluid framework for accurate predictions of trans-critical CO2 processes.
Results of predictions using classical nucleation theory to model homogeneous nucleation of condensation sites in supersaturated vapor regions are presented. A non-equilibrium phase-change model is applied to predict condensation on the nuclei which grow in a dispersed-phase droplet framework. Model validation is provided against experimental data for condensation of supercritical CO2 in a De Laval nozzle including the Wilson line location. The model is then applied for prediction of condensation in the compressor of the Sandia test loop at mildly supercritical inlet conditions. The results suggest that there is sufficient residence time at the conditions analyzed to form localized nucleation sites, however, droplets are expected to be short lived as the model predicts they will rapidly vaporize.