bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rotor-Alone Tones in the Outflow Noise of a Centrifugal Compressor
Authors: Faßbender Armin , Enneking Martin , Jeschke Peter 
Published: November 2019

Abstract
This paper investigates the generation of rotor-alone tones and their contribution to the outflow noise in a transonic centrifugal compressor stage with vaneless diffuser and volute by means of unsteady full-annulus CFD-simulations. The aerodynamic field, as well as the generation and propagation of sound, were simulated simultaneously using the URANS-approach of the solver TRACE and a numerical grid consisting of 170M cells. To assess the accuracy of the predicted fluctuations, the investigation compares the simulated diffuser flow field to measured flow angles and pressure fluctuations obtained from experiments conducted on a large-scale test rig. The analysis explains the different sound generation mechanisms responsible for tonal components in the acoustic spectrum at the compressor outlet, based on the Fourier decomposition of the pressure fluctuations in diffuser and volute. Further, the paper analyzes the modal structure of the simulated sound field at the volute outlet by means of a radial mode analysis and discusses the influence of changing operating conditions on the sound power emitted. The analyses reveal that supersonic flow phenomena occurring at choked operating conditions cause a significant increase in noise emissions. Furthermore, the investigation shows that the sound field at the volute outlet is dominated by few low-order modes, a fact that justifies analysis using methods based on Compressed Sensing in future experimental investigations.
Injector Design Space Exploration for an Ultra-Low NOx Hydrogen Micromix Combustion System
Authors: Agarwal Parash , Sun Xiaoxiao , Gauthier Pierre Q. , Sethi Vishal 
Published: November 2019

Abstract
The depletion of fossil fuel resources, as well as the increasing environmental concerns have become the driving forces towards the research and development necessary for the introduction of alternative fuel such as hydrogen into civil aviation. Hydrogen is a suitable energy source primarily because it is free of carbon and other forms of impurities and is also the most abundant element in the universe. The advantages of using Liquid Hydrogen (LH2) for civil aviation extends beyond carbon-free mission level emissions; LH2 combustion can potentially reduce NOx emission by up to 90%, providing long-term sustainability and unrivalled environmental benefits.
The paper presents a simplified parametric analysis to investigate the influence of various injector design parameters on a hydrogen micromix combustor reactive flow field. The main characteristics investigated are the flame structure (shape and position), the aerodynamic stabilization of the flame and the resulting NOx emissions. The design parameters include variations in the air-feed dimensions and the hydrogen injection diameter. A suitable numerical model was established by comparing various turbulence modelling approaches, reaction mechanisms and turbulence-chemistry interaction modelling schemes. The predictive capabilities, and limitations, of each of these modelling approaches, are assessed. The numerical challenges and limitations associated with modelling H2/air combustion at high pressure and temperature conditions are detailed. The influence of varying the injector design parameters on the mixing and hence the NOx characteristics is assessed.
Erosion in an MI SiC/SiC Ceramic Matrix Composite (CMC)
Authors: Presby M. J. , Gong C. , Kane S. , Kedir N. , Stanley A. , Faucett D. C. , Choi S. R. 
Published: November 2019

Abstract
Erosion phenomenon of ceramic matrix composites (CMCs), attributed to their unique architectural configurations, is markedly different from conventional monolithic ceramic counterparts. Prior to further integration of CMCs into hot-section components of aeroengines subject to erosive environments, their erosion behavior needs to be characterized, analyzed, and formulated. The erosion behavior of a 2-D woven melt-infiltrated (MI) SiC/SiC CMC was assessed in this work as a function of variables such as particle velocity and size. The erosion damage was characterized using appropriate analytical tools such as optical and scanning electron microscopy (SEM). A phenomenological erosion model was developed for SiC/SiC CMC material systems with respect to kinetic energy of impacting particles in conjunction with nominal density, matrix hardness and elastic modulus of the SiC/SiC CMCs. The model was in reasonable agreement with the experimental data.
Reducing Instrumentation Errors Caused by Circumferential Flow Field Variations in Multi-Stage Axial Compressors
Authors: Chilla M. , Pullan G. , Gallimore S. 
Published: November 2019

Abstract
The effects of blade row interactions on stator-mounted instrumentation in axial compressors are investigated using unsteady numerical calculations. The test compressor is an 8-stage machine representative of an aero-engine core compressor. For the unsteady calculations, a 180deg sector (half-annulus) model of the compressor is used.
It is shown that the time-mean flow field in the stator leading edge planes is circumferentially non-uniform. The circumferential variations in stagnation pressure and stagnation temperature respectively reach 4.2% and 1.1% of the local mean. Using spatial wave number analysis, the incoming wakes from the upstream stator rows are identified as the dominant source of the circumferential variations in the front and middle of the compressor, while towards the rear of the compressor, the upstream influence of the eight struts in the exit duct becomes dominant. Based on three circumferential probes, the sampling errors for stagnation pressure and stagnation temperature are calculated as a function of the probe locations. Optimization of the probe locations shows that the sampling error can be reduced by up to 77% by circumferentially redistributing the individual probes. The reductions in the sampling errors translate to reductions in the uncertainties of the overall compressor efficiency and inlet flow capacity by up to 50%.
Recognizing that data from large-scale unsteady calculations is rarely available in the instrumentation phase for a new test rig or engine, a method for approximating the circumferential variations with single harmonics is presented. The construction of the harmonics is based solely on the knowledge of the number of stators in each row and a small number of equi-spaced probes. It is shown how excursions in the sampling error are reduced by increasing the number of circumferential probes.
Optimization Design Analysis of Primary Surface Recuperator for Rotorcraft Powerplant Applications
Authors: Zhang Chengyu , Gümmer Volker 
Published: November 2019

Abstract
The growing demand for highly efficient, environmentally friendly aero-engines highlights the incorporation of recuperators into gas turbine systems, which is especially attractive for rotorcraft powerplants, as the majority of their mission time is spent at part load cruise power (typically above 60%) with the non-optimum specific fuel consumption (SFC) characteristic. In this work, a primary surface recuperator (PSR) for the 300kW-class rotorcraft powerplant is considered for optimization by using a Genetic Algorithm (GA). By the very nature of aero-engines application, two different objective optimizations are conducted, aimed at minimizing the recuperator weight or/and reducing pressure drop, maximizing recuperator effectiveness. The geometries of the surface plate remain constant, while three shape parameters work as variables for defined constraints. The optimization process proves that GA is an adequate tool in recuperator design optimization according to the specified objectives. Based on calculation results, potential recuperator designs for aero-engine application are suggested.
Combustion Instabilities of Separated Stratified Swirling Flames With Different Degrees of Premixedness
Authors: Wang Xinyao , Han Xiao , Hui Xin , Zhang Chi , Song Heng , Lin Yuzhen , Sung Chih-Jen 
Published: November 2019

Abstract
The effects of premixedness degrees on combustion instabilities of separated stratified swirling flames have been investigated experimentally in the Beihang Axial Swirler Independently-Stratified (BASIS) burner. The degree of premixedness is modulated by the fuel split between two injection positions in the outer stream. In the spectra of pressure oscillations, both the dominant frequency and amplitude of partially premixed flames are positively correlated with fuel split ratios. The partially premixed flame is found to feature a large-scale periodic convective motion based on CH* chemiluminescence images, which have been analyzed under different fuel split ratios by a point-to-point Fast Fourier Transform (FFT) method. The development of above convective motion is explained by combining the variation of pressure and heat release in the oscillation period. Local Rayleigh index maps show that the driving factor of combustion instability for the partially premixed flame mainly comes from the upstream of the combustor. Finally, thermoacoustic network analysis is applied to predict observed frequencies under both perfectly and partially premixed conditions. The supposed additional convective time due to equivalence ratio fluctuations and the elongated flame region for the partially premixed flame is validated by its longer time delay in the sensitivity analysis of the n-τ flame model.
Compression Technology Selection for Downhole Application in Gas Wells
Authors: Malkawi Ameen , AlAdawy Ahmed , Gadamsetty Rajesh Kumar V. , Lastra Melo Rafael 
Published: November 2019

Abstract
Downhole gas compression technology is an artificial lift method that aims to boost production, maximize recovery and delay onset of liquid loading in gas wells. There are different available compression technologies that can be considered for downhole applications, such as screw, scroll, centrifugal and axial compressors. Selection of the appropriate type mainly depends on expected well performance, ambient conditions, compressor operating envelope, technology characteristics, limitations and size constraints. The objective of this study is to perform a feasibility evaluation of compression solutions applicable for a given set of candidate gas wells.
Aerodynamic and hydraulic models are used to determine operating conditions, compressor performance, and to select equipment specifications such as impeller diameter, compressor envelope, shaft HP requirement and number of stages among other parameters. A Pugh analysis is performed for all compression technologies and their characteristics to down-select the most suitable solutions for the given set of wells.
The results of the analysis indicated an optimal downhole compression technology that covers most of the gas flow rate requirements and meet the performance expectations. The study also provided critical specifications for the compressor, including high-speed operation needed to provide the required flow rates and compression ratio for a relatively small housing diameter. The study also finds that other technologies may be applicable but only to certain population of wells, as the flow rate spectrum is narrower than the optimal solution at the studied conditions. The analysis for the discarded compression technologies in this study showed relatively significant disadvantages for downhole application when compared to the selected compressor.
This study presents a holistic analysis for compression technology selection for gas wells that, as per to the understanding of the authors, is unique in the existing literature of gas well applications.
Flow-Driven Design Optimization of Centrifugal Compressor Volutes for Turbochargers
Authors: Tanganelli Andrea , Andreini Giulia , Rossini Matteo , Balduzzi Francesco , Bianchini Alessandro , Ferrara Giovanni 
Published: November 2019

Abstract
The design of the volute (in terms of area distribution and shape of the cross section) has a relevant impact on the efficiency and the operating range of a centrifugal compressor. This latter aspect is even more relevant in turbochargers, where the compressor has to cover a functioning range much wider than that of industrial applications. In addition, beyond conventional aerodynamic requirements, the design of the cross section shape is driven often in these applications also by space constraints imposed by the vehicle layout, leading to a variety of volute layouts. In a previous study, some of the authors highlighted the prospects of using the entropy generation rate to evaluate the losses within a volute, since this parameter allows an exact localization of irreversibilities. Starting from these results, the present study shows the suitability of this parameter as an indicator for the fine design optimization of the volute shape. A methodology is presented, which, based on the CFD computed contours of both the entropy generation rate and the total pressure, is able to drive the fine optimization of the volute cross-section at different azimuthal positions in order to maximize its efficiency. Multiple volute shapes are analysed in the paper and the effect of the operating conditions is accounted for by investigating different mass flow rates. The proposed approach indeed lead to a maximization of the volute efficiency with only a few trials and it could indeed provide room for future automatized fine optimization strategies.
Validation of a Numerical Quasi One-Dimensional Model for Wave Rotor Turbines With Curved Channels
Authors: Tüchler Stefan , Copeland Colin D. 
Published: November 2019

Abstract
A wave rotor is a shock-driven pressure exchange device that, whilst relatively rarely studied or indeed, employed, offers significant potential efficiency gains in a variety of applications including refrigeration and gas turbine topping cycles. This paper introduces a quasi one-dimensional wave action model implemented in MATLAB for the computation of the unsteady flow field and performance characteristics of wave rotors of straight or cambered channel profiles. The purpose here is to introduce and validate a rapid but reliable method of modelling the performance of a power-generating wave rotor where little such insight exists in open literature. The model numerically solves the laminar one-dimensional Navier-Stokes equations using a two-step Richtmyer TVD scheme with minmod flux limiter. Additional source terms account for viscous losses, wall heat transfer, flow leakage between rotor and stator endplates as well as torque generation through momentum change.
Model validation was conducted in two steps. First of all, unsteady and steady predictive capabilities were tested on three-port pressure divider rotors from open literature. The results show that both steady port flow conditions as well as the wave action within the rotor can be predicted with good agreement. Further validation was done on an in-house developed and experimentally tested four-port, three-cycle, throughflow micro wave rotor turbine featuring symmetrically cambered passage walls aimed at delivering approximately 500 W of shaft power. The numerical results depict trends for pressure ratio, shaft power and outlet temperature reasonably well. However, the results also highlight the need to accurately measure leakage gaps when the machine is running in thermal equilibrium.
The Impact of Model Assumptions on the CFD Assisted Design of Gas Turbine Packages
Authors: Lucherini Gabriele , Michelassi Vittorio , Minotti Stefano 
Published: November 2019

Abstract
A gas turbine is usually installed inside a package to reduce the acoustics emissions and protect against adverse environmental conditions. An enclosure ventilation system is keeps temperatures under acceptable limits and dilutes any potentially explosive accumulation of gas due to unexpected leakages. The functional and structural integrity as well as certification needs of the instrumentation and auxiliary systems in the package require that temperatures do not exceed a given threshold. Moreover, accidental fuel gas leakages inside the package must be studied in detail for safety purposes as required by ISO21789. CFD is routinely used in BHGE (Baker Hughes, a GE Company) to assist in the design and verification of the complete enclosure and ventilation system. This may require multiple CFD runs of very complex domains and flow fields in several operating conditions, with a large computational effort. Modeling assumptions and simulation set-up in terms of turbulence and thermal models, and the steady or unsteady nature of the simulations must be carefully assessed. In order to find a good compromise between accuracy and computational effort the present work focuses on the analysis of three different approaches, RANS, URANS and Hybrid-LES. The different computational approaches are first applied to an isothermal scaled-down model for validation purposes where it was possible to determine the impact of the large-scale flow unsteadiness and compare with measurements. Then, the analysis proceeds to a full-scale real aero-derivative gas turbine package. in which the aero and thermal field were investigated by a set of URANS and Hybrid-LES that includes the heat released by the engine. The different approaches are compared by analyzing flow and temperature fields. Finally, an accidental gas leak and the subsequent gas diffusion and/or accumulation inside the package are studied and compared. The outcome of this work highlights how the most suitable approach to be followed for industrial purposes depends on the goal of the CFD study and on the specific scenario, such as NPI Program or RQS Project.
Impact of the Reaction Mechanism Model on Soot Growth and Oxidation in Laminar and Turbulent Flames
Authors: Tardelli Livia , Franzelli Benedetta , Rodrigues Pedro , Darabiha Nasser 
Published: November 2019

Abstract
Numerical prediction of soot production in turbulent flames is extremely challenging, as it involves complex physical and chemical processes whose modeling presents today many uncertainties. The modeling of soot growth and oxidation reactions is a key aspect for soot prediction accuracy, as it may greatly contribute to the soot mass yield as numerically observed by Rodrigues et al. [1] in a turbulent non-premixed ethylene-airflame. Surface reactions are commonly described by a HACA-based model that is known to provide good agreement with experimental data in laminar premixed flames, while failing the description of laminar diffusion flames. A modification of the HACA-RC model [2], which is an extended version of the original HACA mechanism [3], is proposed here based on the work of Hwang et al. [4] in order to obtain a soot model that performs reasonably well on both premixed and diffusion laminar flames. To assess its accurary validations are performed on different laminar flames by comparison with available experimental data. Then, the impact of such modification on the prediction of turbulent flames is evaluated by performing two Large Eddy Simulations (LES) of a model gas turbine combustor using the new model and the reference HACA-RC model. The obtained results are compared to the experimental data in terms of soot volume fraction. Discrepancies between the two LES results are finally explained by analyzing the different source terms of soot production.
Measurement Drift in 3-Hole Yaw Pressure Probes From 5 Micron Sand Fouling at 1050° C
Authors: Turner Edward J. , Bogdan Matthew F. , O’Connell Tyler M. , Ng Wing F. , Lowe Kevin T. , Crook Loren , Stevenson Richard , Roberts James 
Published: November 2019

Abstract
The present paper focuses on the resilience of 3-hole pressure probes to hot sand fouling in turbomachinery environments. These probes are utilized inside jet engine hot sections for diagnostics and flow characterization. Ingestion of sand and other particulates pose a significant risk to hot section components and measurement devices in gas turbine engines. In this study, wedge, cylindrical, and trapezoidal probes were exposed to hot section turbine aerothermal conditions of 1050°C and 65–70 m/s flow velocity and fouled with 0–5 μm Arizona Road Dust (ARD). Sand accumulated more rapidly on the surface of the trapezoidal and cylindrical probe geometries than on the surface of the wedge probe geometry.
Probe calibrations following sand fouling were performed in an ambient temperature, open air, calibration jet at Mach 0.3 and 0.5. Calibration curves using non-dimensional coefficients were used to assess probe error in yaw angle due to sand fouling. Probe error was based on each probe’s ability to accurately measure flow direction over a flow angle range of [−10°, 10°]. On average, the probes displayed greater error at Mach 0.5 than Mach 0.3. The wedge probe performed the best after sand fouling and displayed a maximum error of less than ±2° in yaw angle. In contrast, the cylindrical probe performed the worst after sand fouling and displayed maximum errors of more than ±8° in yaw angle. Transient response did not change notably with sand fouling.
Disappearing Thermo-Economic Sanity in Gas Turbine Combined Cycle Ratings: A Critique
Authors: Gülen S. Can 
Published: November 2019

Abstract
There is very little doubt that there has been a noticeable advance in heavy-duty industrial gas turbine technology for utility scale electric power generation in the last decade. In keeping with the first six decades of the technology (roughly 1950 through 2010), the main drivers in increasing thermal efficiency and megawatt ratings have been increasing turbine inlet temperature and airflow. In accordance with the basic thermodynamic principles governing the underlying Brayton cycle, compressor pressure ratio kept pace with them.
It is hard to quibble about the 40+ percent in rated thermal efficiency in simple cycle. If projected turbine inlet temperatures and cycle pressure ratios can be sustained in the field, current state-of-the-art in turbine hot gas path metallurgy, coatings and advanced film cooling techniques indeed support published ratings. Unfortunately, published combined cycle ratings are an altogether different matter. It is one thing to set the product line rating performance at an aggressive level with well-understood albeit optimistic assumptions such as very low water-cooled steam turbine condenser pressure with open-loop cooling. It is yet another thing to blatantly disregard fundamental laws of thermodynamics with outlandish performance ratings, which are unlikely to materialize even in the next decade or two cost-effectively (unless an unforeseen transformative step-change in technology materializes). In this paper, using fundamental thermodynamic arguments and detailed heat and mass balance simulations, it will be shown that some, if not all, OEM ratings are losing touch with reality.