bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Dirt Deposition on Double-Walled Combustor Liner Geometries
Authors: Fallon Brandon , McFerran Kyle , Fox Sarah , Thole Karen A. , Lynch Stephen P. , Lundgreen Ryan , Kramer Stephen P.
Published: September 2023

Gas turbine engines are frequently subjected to particle laden flows in which dirt and sand are ingested into the hot section. The particles enter internal cooling channels where they deposit and block cooling features, creating increased heat transfer, reduced flows, and diminished cooling performance. This study investigates geometries with the intention of mitigating dirt effects on cooling for double-walled combustor liners that use impingement and effusion cooling. Dirt particulate was injected into several double-walled coupons at room temperature using two feed modes: slug and continuous. Slug feed tests used controlled bursts of dirt whereas continuous feed provided a steady stream of dirt. Computational studies were also conducted to investigate internal flow fields between the impingement and effusion plates. The best performing geometry that was tested in terms of the lowest measured dirt capture had pins and cones extruded from the cold-side of the effusion plate. The flow parameter was found to scale the dirt capture with higher capture efficiency at higher flow parameters.
Sand Ingress in Gas Turbines Operating in Desert Environments: Observations and CFD Simulations
Authors: Tayebi Kamel-Abdelkader , Nair Sumith , Jupudi Maruthi Manohar , Dawood Alaaeldin , Khalidi Abdurrahman
Published: September 2023

Gas Turbines operating in desert and dusty environments inherently pull air that is contaminated with particles of sand/dust. In certain conditions of filter bypass, these particles find their way to the cold and hot sections of the gas turbine affecting performance and parts fitness for use, sometimes leading to forced outages and expensive parts repair and replacement.

In the first part of this paper, we describe some observations from cases in the Middle East. In the second part of the paper, we present the results of CFD simulations of sand ingress through the air filtration house and into the compressor of a gas turbine operating in a desert environment. Simulations are performed at increasing levels of contamination. We discuss the influence of ingested particles size and distribution as they relate to the level of contamination observed in desert environments including the case of severe sandstorms.
Effect of Inflow Swirl on the Sealing Effectiveness of Turbine Rim Seal
Authors: Cong Qingfeng , Lei Long , Zhang Kaiyuan , Li Zhigang , Li Jun
Published: September 2023

Turbine inlet swirl condition is inherently present at the combustion chamber outlet and has an important influence on mainstream flow and gas ingestion. The sealing effectiveness and ingestion mechanism were numerically investigated using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations coupled with a fully developed shear stress transport (SST) turbulent model. Mass transfer analogy is utilized to simulate the hot gas ingestion and sealant egress by seeding CO2 into the air as a tracer gas. Simulations with mainstream inflow swirls of 0°, ±10°, ±20° were conducted and compared. Computational results indicate that at the same sealant flow rate, the sealing effectiveness increases significantly with the increase in the incidence angle at the leading edge of stationary vanes. When the non-dimensional sealant rate is 0.02415 and the incidence angle is increased from 0° to +10° and +20°, the sealing effectiveness at r/b = 0.958 on stationary disk is increased by 3.39% and 13.26%, respectively. The area-averaged sealing effectiveness of +20° incidence angles at the stationary and rotating disk can be increased by 12.02% and 5.19%, compared with the 0° incidence angle. The incidence angle near the vane leading edge affects the formation position of the horseshoe vortex, and ultimately affects the passage vortex. Therefore, the flow field in the rim seal clearance changes greatly. From axial and radial perspectives, the vortex due to Kelvin Helmholtz instability increases the blockage of axial rim seal clearance with the increase in incidence angle. From a circumferential perspective, as the incidence angle increases, a vortex structure is induced at the entrance of the rim seal, and the radial scale of the vortex decreases and the axial scale increases. All variations can gradually weaken the gas ingestion and improve the sealing effectiveness in the disk cavity. Based on fast Fourier transform (FFT) and analyzing the unsteady mass flow rate of ingress through the rim seal, the influence of the vortex due to Kelvin Helmholtz instability with a period of about 20 time-steps plays a major role in influencing sealing performance. The sealing effectiveness and flow pattern in the rim seal clearance have strong unsteady characteristics with this period.
Experimental Study of a Low NOx and Soot Injection System for Spinning Combustion Technology: Characterization of Soot and NO Formation Under Realistic Operating Conditions by Laser Diagnostics
Authors: Milea Andrei-Silviu , Perrier Aurélien , Caceres Marcos , Vandel Alexis , Godard Gilles , Renard Fabien , Duchaine Patrick , Richard Stephane , Cabot Gilles , Grisch Frédéric
Published: September 2023

In the context of air pollution, Safran Helicopter Engines patented an innovative design for helicopter combustors based on Spinning Combustion Technology. The development focuses on novel concepts of kerosene fuel injectors aiming to further reduce NOx and soot particle emissions. Experimental studies are performed on the fuel injectors in a high-pressure/high-temperature combustion facility designed by the CORIA laboratory. This test bench is able to reproduce the same conditions encountered in a helicopter combustor over the entire range of nominal operating conditions and has large optical accesses for the implementation of optical diagnostics. NOx and soot particles are assessed during three experimental studies, two of which focus on each pollutant individually and a third one specially dedicated for high-speed velocity measurements by PIV. Soot particles distribution, flame structure and fuel distribution were obtained by coupling the PLIF-OH, PLIF-kerosene and PLII diagnostics. On the other hand, the PLIF-NO combined with PLIF-OH and PLIF-kerosene allows to study the formation of NO with the combustion process and the fuel distribution.
Generation of Entropy Waves by Fully Premixed Flames in a Non-Adiabatic Combustor With Hydrogen Enrichment
Authors: Eder Alexander J. , Dharmaputra Bayu , Désor Marcel , Silva Camilo F. , Garcia Alex M. , Schuermans Bruno , Noiray Nicolas , Polifke Wolfgang
Published: September 2023

Thermoacoustic combustion instability is a major concern in gas turbine combustors with hydrogen-enriched fuels. Unsteady combustion not only generates acoustic waves, but it may also result in fluctuations of burnt gas temperature, referred to as entropy waves. They are convected by the mean flow through the combustor and can cause indirect combustion noise when they are accelerated at the exit. In this work, we demonstrate that entropy waves occur in a fully premixed burner due to unsteady heat transfer at the combustion chamber wall. This mechanism of entropy generation is often neglected in the literature. This work shows an additional mechanism in CH4-H2-air flames, through which entropy may be created even in the fully premixed case. This is due to differential diffusion which generates local fluctuations in equivalence and carbon-to-hydrogen ratios. An adiabatic flame temperature is defined based on these two quantities to examine the influence of differential diffusion on the generation of entropy fluctuations. The generation of entropy waves is investigated by applying system identification (SI) to time series data obtained from a broadband forced large eddy simulation (LES) coupled with a heat conduction solver. The entropy transfer function (ETF) and flame transfer function (FTF) identified are then compared to experimental data obtained with tunable diode laser absorption spectroscopy with wavelength modulation spectroscopy (TDLAS-WMS) for measuring temperature fluctuations, and the multi-microphone method (MMM), respectively. After validating the computational setup, the entropy frequency response is identified at various positions within the combustion chamber, and the effects of generation and convective dispersion of entropy waves are qualitatively investigated. We show that a fully premixed turbulent system may exhibit significant entropy waves caused by wall heat losses and differential diffusion of hydrogen.
A Novel Prediction Model for the Aerodynamic Losses Increase Due to Film Cooling Injections From Gas Turbine Vane Surface
Authors: Wang Yulin , Guo Can , Chen Xinnan , Sun Tianyi , Chen Dawei , Li Zhigang , Li Jun
Published: September 2023

In this paper, experimental and numerical investigations were conducted on the aerodynamic performance of a turbine vane cascade with film cooling injections. The impact of coolant injection on aerodynamic losses was investigated, and thus a novel prediction model was proposed to estimate the aerodynamic penalty associated with film cooling injections. Three-dimensional numerical simulations performed in this paper were based on the commercial CFD solver ANSYS CFX. To analyze the effects of hole position on the aerodynamic performance, a validated computational model was proposed for the turbine vane cascade with single row film holes either on the suction surface, the leading edge, or the pressure surface. Total pressure loss coefficients were further evaluated and analyzed for typical ranges of blowing ratio (0.5 to 1.5) and coolant injection angle. It is found that, total pressure loss coefficients increase with increasing blowing ratio to different extent depending on the hole position, and the loss associated with coolant injection from the suction surface are highest. Using co-relation mathematical models to predict the penalty is challenging due to the complicated three-dimensional flow structure. The applicability and accuracy of a published loss model, Hartsel model, were evaluated in this study. The prediction of Hartsel model showed largely dependent on the local Mach number of mainstream and the velocity of coolant injection. This suggests that the Hartsel model can’t predict total pressure losses for various locations of turbine airfoil cascade well. For these reason, this present work further develop the applicability and accuracy of the Hartsel model to a satisfactory level. Results indicate that the present model can accurately predict total pressure loss coefficients of film holes at different positions when the blowing ratio is in the range of 0.5 to 1.5 and the incidence angle of cooling air varies in a specified extend.
Methods for the Preliminary Design of Heat Exchangers in Aircraft Engines
Authors: Schmelcher Marc , Häßy Jannik , Görtz Alexander , El-Soueidan Mahmoud
Published: September 2023

The Water-Enhanced Turbofan (WET) is a promising approach to increase engine efficiency and to reduce emissions. For this concept, a Heat Recovery Steam Generator (HRSG) is required to evaporate and superheat liquid water before injecting it into the combustor. However, the integration of a HRSG into an aero engine has not been investigated in detail yet and the design specifications as well as metrics differ from state of the art, ground-based HRSG applications. Therefore, this paper presents methods and correlations that are combined to build a preliminary design tool for heat exchangers with evaporation. The resulting model is verified by a comparison to experimental heat exchanger studies. Finally, the model is used to assess a HRSG located downstream of the turbine section of a generic aero engine evaporating different water mass flows. The large differences in exhaust temperature and mass flow between cruise and take-off conditions outline the difficulty in finding a well balanced HRSG design.
Impact of High-Pressure-Turbine Purge Flow on the Evolution of Turbulence in a Turbine Vane Frame
Authors: Hafizovic Asim , Merli Filippo , Krajnc Nicolas , Schien Malte , Peters Andreas , Heitmeir Franz , Göttlich Emil
Published: September 2023

This paper describes the measurement and postprocessing of turbulence data. The experiments were carried out in a two-stage two spool transonic turbine test rig at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology, which includes relevant purge and turbine rotor tip leakage flows. The test setup consists of a high-pressure turbine (HPT) stage, a turbine vane frame (TVF) with turning struts and splitters and a counter-rotating low-pressure turbine (LPT) to allow engine realistic measurements. Time-resolved area traverse measurements have been performed for three different operating conditions in three measurement planes downstream of the HPT rotor, which enable the measurement of the turbulence quantities at the TVF inlet and outlet as well as LPT outlet. The turbulence quantities are evaluated using triaxial- and single hot-film probes by means of Constant-Temperature-Anemometry, and their results were validated with Five-Hole Probe (FHP) measurements. Ensemble- and time-averaging as well as Fourier transforms, were applied for data reduction.

It is shown how the turbulence intensity and integral length scale vary over different purge flow rates (PFR). The acquired measurement data illustrates that the interaction of the ejected purge flow with mean flow enhances the turbulent mixing in the secondary flow structures at the TVF inlet and TVF outlet, respectively. Furthermore, the flow downstream of the LPT rotor is affected by TVF and LPT rotor secondary flow structures, which are identified as high turbulence regions. These regions strongly depend on the purge flow rate. These results acquired under engine realistic rigs flow conditions enable a deeper understanding of the relationship between loss and turbulence quantities and will help improve the application of CFD turbulence models to turbomachinery modeling.
A Probabilistic Model of Icing Induced Fan Unbalance
Authors: Liao Shengfang
Published: September 2023

A probabilistic model has been developed to simulate the fan unbalance caused by the ice accretion and shedding. The non-uniform ice shedding around the fan circumference was modeled by applying variations of ice adhesion strength to the fan blades. A simple ice accretion/shedding process was simulated with simplified fan blade geometries. Monte Carlo simulations were conducted for large samples of fan blades with randomly assigned ice adhesion strength. The mean and the standard deviation of the maximum fan unbalance were derived from the Monte Carlo simulations. The model is able to capture the major trends of the fan unbalance against various parameters. The mean fan unbalance was found to increase with decreasing fan speed, increasing ice adhesion strength. The unbalance sensitivity to the ice adhesion variations depends on the water impingement profiles. There exists a water impingement radial profile, 1/r-profile, that causes the worst fan unbalances. Finally, non-dimensional fan unbalance and centrifugal force are proposed to scale the fan unbalance from one engine to another engine of different size.
Brush Seal Wear Measurements for High-Speed, High-Temperature, Low-Pressure-Turbine Applications
Authors: Versluis Joris , Mosbacher Mike , Göttler Johann , Mandard Romain
Published: September 2023

This paper presents results of measurements with brush seals in a test-rig mainly operating at high speed and high temperature conditions. The measurements were carried out to investigate wear mechanisms, seal wear rates a nd the effect on seal clearance. A new optical measurement system for the purpose of the experiments with brush seals was developed allowing an accurate setting of the eccentric interference during the rub tests. Various types of tests were carried out to cover the different types of rub experienced within the operating range of a low pressure turbine. Known wear mechanisms reported in earlier publications and also from in-house experience were confirmed during the test campaign and recent experiences with rotor wear due to brush seal contact could be reproduced on the rig and are now much better understood. Cyclic tests also showed the behavior of the seal over time and provided new insights into the dependencies of bristle wear and operating conditions. Additionally some comparisons of the results with field data were made to draw first conclusions regarding the relevance of the tests for the real life applications.
Innovative Air Bypass System for Low-Emission Multi Can Combustors
Authors: Ćosić Bernhard , Wassmer Dominik , Reiß Frank , Kluß David , Pähr Judith , Reumschüssel Johann Moritz , Beuth Jan Paul , Szeponik Martin , Reichel Thoralf , Paschereit Christian Oliver
Published: September 2023

Gas turbines that are used as compressor drives are often operated in the part load regime because compressor stations are usually designed for operation with full power at extreme weather conditions. Consequently, these gas turbines must comply with strict emission regulations at unfavorably low turbine inlet temperatures. To extend the low emissions operation range of the premixed combustion systems, many gas turbines bypass a part of the compressed air upstream of the combustor and either blow it off into the exhaust stack or reinject it into the secondary combustion zone. The first approach is the more common one but has the disadvantage of increasing the gas turbine fuel consumption and thus the CO2 emissions. The second approach avoids this disadvantage but is very challenging in terms of actual mechanical integration into the gas turbine. This paper presents a new approach that overcomes shortcomings by injecting the compressed air in the burner head in the vicinity of the primary combustion zone. This is particularly attractive for multi can combustors like these employed for the MAN industrial gas turbine family.

Atmospheric combustion tests are conducted for two different air injection designs. The first design features lower air injection velocity and the second features higher injection velocities. Both injection strategies are tested with the industrial MGT gas turbine can combustor. It features 4 MW of thermal power at full pressure and full load conditions. It is an ultra-low emission premixed swirl combustor with a radial swirler design. The full size burner is tested at atmospheric conditions in a burner test rig with a quartz flame tube and natural gas as fuel. The performance of the air bypass system is assessed by means of CO and NOx emission measurements for different air bypass ratios and is compared with high-pressure measurements without an air bypass system. Additionally, OH* chemiluminescence camera pictures are presented and compared to CFD calculations. It is found that the air injection in the annular vicinity of the swirl flame does not cause increased CO emissions by quenching or other effects. For the investigated setup, it is more favorable to inject the air at low velocities because this strategy causes less interaction between bypass air and premixed flame.
Numerical Analysis of High Frequency Transverse Instabilities in a Can-Type Combustor
Authors: Jella Sandeep , Füri Marc , Katsapis Vasilis
Published: September 2023

Dry Low Emissions (DLE) systems are well-known to be susceptible to thermoacoustic instabilities. In particular, transverse, spinning modes of high frequency can lead to severe hardware damage in a matter of seconds. The thermoacoustic response of an engine is specific to the combustor geometry, operating conditions and difficult to reproduce at the lab-scale. In this work, details of high frequency dynamics observed during the early development phase of a new DLE system are provided, where a multi-peaked spectrum was noticed during rig-testing. Beginning with an analysis of the measured pressure spectra and the natural resonance frequencies of three different concepts, an analytical model of the clockwise and anti-clockwise transverse waves was fitted to the experimental data using a non-linear curve fitting approach to produce a simple yet useful understanding of the phenomena. A flamelet-based Large Eddy Simulation (LES) of the entire system was used to complement this analysis and confirm the mode shapes using dynamic mode decomposition (DMD). Both approaches independently identified a spinning second order mode as the dominant one in the high frequency regime. The LES indicated that precessing vortex core dynamics tend to impose a deformation (in the circumferential direction) on the outer shear layer vorticity magnitudes. Flame anchoring in this shear layer is suggested as a possible cause for the onset of instability. With regard to modeling sensitivities, it is shown that sub-grid scale combustion modeling has a strong impact on predicted amplitudes. Ultimately, a thickened-flame model with a modified efficiency function provided consistent results.
Collision Mechanism and Dynamic Response of Rotor System With Pedestal Looseness
Authors: Dai Qiyao , Sun Bo , Chen Xueqi , Ma Yanhong
Published: September 2023

In the structural design of aeroengine multi fulcrum flexible rotor, due to the limitation of assembly conditions and working load environment, there is a certain fit clearance between the bearing outer ring and the bearing pedestal, which is called pedestal looseness. When the response amplitude is high, the outer ring and pedestal collide, which affects the dynamic characteristics of the rotor system. Previous research often characterize the collision caused by pedestal looseness on the rotor as a nonlinear stiffness term in the rotor dynamics model, which can not directly reflect the real collision mechanism of the rotor. In this paper, the mechanical model of flexible rotor system with pedestal looseness was established. The motion variation process of rotor when collision occurred and subjected to radial impact was analyzed, which is characterized as the collision force of rotor, and the dynamic response is obtained. The results showed that when the response amplitude is large, rotor and bearing pedestal collided periodically, and various combination frequencies of rotation frequency and collision characteristic frequencies appeared in dynamic response; the combination frequencies may be equal to the modal frequency of the rotor system at the non critical speed point, so that the rotor may still have a large response amplitude when the speed is far from the critical speed.
Experimental Analysis of the Hydrogen Capability of a Fuel Flexible Jet Stabilized Syngas Micro Gas Turbine Combustor Under Atmospheric Conditions
Authors: Hohloch Martina , Lingstädt Timo , Kutne Peter
Published: September 2023

In this study the hydrogen capability of a jet-stabilized combustion system, initially designed/or syntheses-gas from biomass and natural gas mixtures, was investigated at atmospheric conditions. Therefore it was operated with mixtures of natural gas with hydrogen, from pure natural gas to pure hydrogen. In addition, different operational concepts for the pilot stage and their influence on the stability of the combustion and emissions were tested. The investigations were performed in an atmospheric test rig. The test rig offers optical access to the combustion zone by a cylindric quartz glass tube. It is equipped with thermocouples, pressure probes and mass flow meters. The incoming air was preheated up to 600 °C. During the investigations the parameters burner air number and thermal power were varied. The analysis of the flame was done using OH*-chemiluminescence measurement. The emissions were quantified using gas analyzer systems to detect CO, CO2, NOx, O2 and UHC concentration. The position of the flame and the emissions are discussed. The results show that the combustor is able to deal with all tested mixtures of natural gas and hydrogen up to 100% of hydrogen. The results of the measurement campaign were used to validate CFD simulations. In this publication both experimental results and corresponding simulations are shown and assessed.
Transient Tip Clearance Prediction Model Considering Transient Radial Temperature Distribution of Discs in a Gas Turbine Engine
Authors: Wei Jie , Yang Heli , Zheng Pengbo , Wang Baotong , Zheng Xinqian
Published: September 2023

The tip clearance of turbomachinery components, such as compressor and turbine, significantly impacts gas turbine engine performance, including the thrust and fuel consumption. Therefore, an appropriate prediction of turbomachinery tip clearance and active clearance control is indispensable in improving engine performance. The traditional 1D transient tip clearance prediction model does not consider the radial temperature distribution of the disk (also called disc). However, as the engine performance keeps improving, the disk’s radial temperature gradient also increases. In order to maintain the prediction accuracy within an acceptable range, a generic transient tip clearance prediction model is developed in this paper. Based on the special treatment of the complex axial and radial convective heat transfer boundary regions of the disk, a 2D transient heat transfer model is established, and the radial temperature of the disk is predicted. At the same time, to further improve the prediction accuracy, the thermal expansion interaction between the two different layers of the shroud is studied. In addition, the centrifugal deformation of the blade and disk with variable thickness characteristics are considered in the new transient model. Compared with the traditional 1D transient prediction model, the model developed in this paper further improves the predicting accuracy of the transient tip clearance, which is verified by the high-fidelity fluid-solid-thermal coupling method. The prediction model provides a useful tool for evaluating transient tip clearance. It may also benefit the future design strategy of active clearance control.
Wind Tunnel and OpenFOAM Flow Analysis of a High Solidity Vertical-Axis Wind Turbine
Authors: Yosry Ahmed G. , Álvarez Álvarez Eduardo , Espina Valdés Rodolfo , Fernández Francos Joaquín , Blanco Marigorta Eduardo
Published: September 2023

In the present study, a combination of experimental and numerical investigation has been carried out to ascertain the aerodynamics and the performance characteristics of a small-scale vertical axis turbine model, with a high solidity value. Experimentally, the turbine model has been designed and fabricated using Fused Deposition Modeling (FDM). Tests have been performed in an open-circuit wind tunnel for a velocity range from 7.0 m/s to 10.0 m/s. The non-dimensional tip speed ratio and power coefficient characteristic curves show that the turbine rotor works smoothly under open-field conditions. Computationally, three-dimensional unsteady simulations have been developed using the open-source software OpenFOAM to obtain a comprehensive insight into the aerodynamics and the flow field around the high solidity rotor. The pimpleFOAM solver has been selected for the current code. A good match between the experimental and the OpenFOAM code results has been found, validating the description of the flow physics around the turbine rotor. Also, the vortex street generated by the turbine blades and the ending plates has been visualized.
Effects of Riblet Dimensions on the Transitional Boundary Layers Over High-Lift Turbine Blades
Authors: Ananth S. M. , Nardini Massimiliano , Vaid Aditya , Kozul Melissa , Vadlamani Nagabhushana Rao , Sandberg Richard D.
Published: September 2023

Substantial research exists in the literature on reducing the profile loss of transitional boundary layers over low-pressure turbine (LPT) blades via different mechanisms such as free-stream turbulence, upstream wakes, and surface roughness. These mechanisms have proven to be beneficial in mitigating the separation bubble-related losses in ultra-high lift blade designs, despite an increase in the loss due to increased turbulent wetted area (TWA). In this work, we adopt a strategy of employing surface roughness in the transitional regime to minimize the separation bubble-related losses and flush mounted riblets downstream to further mitigate the skin-friction drag and boundary layer losses due to an increase in the TWA. Several high-fidelity scale resolving simulations are performed on this ‘rough-ribbed blade surface’ to discern the effect of varying the riblet spacing (s+) and height (h+). The streamwise evolution of skin-friction coefficient, boundary layer integral parameters and shape factor are compared and contrasted among riblets of different dimensions. The instantaneous flow features and second order statistics such as the Reynolds stress, turbulent kinetic energy and its production are analyzed for different test cases to determine the impact of riblets on these quantities. When compared to the roughness alone configuration, the scalloped shape riblets with s+ = 17 and h+ = 22 reduced the net skin-friction drag by 7.3% and the trailing edge momentum thickness by 14.5% thereby demonstrating the efficacy of riblets in reducing the mixing losses under adverse pressure gradients. Through an analysis of flow blockage introduced by the application of riblets, the deleterious effects of increasing the riblet height along with the necessity of optimizing the riblet ramp are highlighted.
Life Cycle Analysis of SiC Samples in a Stagnation-Point Reacting Flow
Authors: Nair Chinmay , Cooper John , Cha Chong M. , Chelliah Harsha K.
Published: September 2023

A laboratory scale high-pressure flow reactor has been developed to study the interaction of a steam jet with various advanced ceramic and environmental barrier coating materials. Previous research studies were conducted at close to atmospheric pressure and have proposed an empirical relation for material surface recession. But none of them have been able to extract a pressure dependence factor with high fidelity. To address this deficiency, in the present study test conditions of steam at 1400 Celsius, pressures up to 5 atm, and velocities exceeding 200 m/s (positioned at 1 mm from the surface and at variable impinging angles) have been considered. These conditions mimic the local water molecule number density and velocity in actual gas turbine engine components, with test duration exceeding 24 hours. The initial life cycle data of Chemical Vapour Deposited Silicon Carbide (CVD SiC) interactions with water vapour show very interesting physical and chemical mechanisms controlling the recession rates. Complementary well-resolved computational fluid dynamic simulations have been performed to support the experimental setup and results, shedding new insight into the role of stagnation regions in the flow field where the flow residence times are the highest.
Development and Experimental Validation of a Model-Based Balancing Prediction Method for Bowed Rotor
Authors: Checcacci Damaso , Ferraro Riccardo , Girezzi Gabriele , Mitaritonna Nicola , Orazi Claudio
Published: September 2023

Rotor balancing is one of the most discussed topics in the field of rotor-dynamics. It is very important in the industrial practice and sometimes there are very particular cases that cannot be addressed and solved by traditional methods.

The rotor model addressed in this paper has been initially presented in a previous work [1], with the aim to introduce a procedure for “predicting the effects of balancing” at rotational speeds that are higher than those possible on balancing machines.

In this work, the balancing of the same rotor model is addressed by a maintenance standpoint, considering the case of a rotor showing bending at its neutral axis. This situation may be present, for several reasons, in rotors sent to the Original Equipment Manufacturers (OEMs) for repair/refurbishment after several years of operation, or as consequence of emergency events that may cause local deformation and/or require significant re-machining. To some extent, this situation can still allow for High-Speed Balancing (HSB) of such shafts. Nonetheless the availability of prediction models able to evaluate in a relatively short time the feasibility of HSB, in advance of starting any hardware activity, is of paramount importance to avoid costs and time impacts.

In this paper, a procedure to address the feasibility of balancing of an industrial steam turbine rotor, starting from runout measurement of its bowed shape, is presented. Hence, results of several approaches are discussed for identification of their limits of applicability. Eventually the result of an analytical model including the deflected shape of the shaft is compared with HSB runs.
Methodical Evaluation of Process Chains for the Manufacturing Of Rotating Engine Components – Blisk | IBR
Authors: Seimann Martin , Heinen Daniel , Cassel Leonard , Bergs Thomas
Published: September 2023

In future, component requirements of blade integrated disks (Blisk) / integrally bladed rotors (IBR) as well as turbine and compressor discs will become more challenging as today exhibiting more complex and downsized geometries, tighter tolerances and are made of more difficult to machine materials (e.g. advanced Ni- and Ti-alloys). This means that the process portfolio is getting significantly broader as components will not be manufacturable as of today mainly using conventional technologies. Adaptive process chains are required, specifically developed for each component.

To decide which process chains are feasible and which are most suitable the paper describes the approach of developing a modular evaluation methodology. The methodology considers process capabilities of the manufacturing technology as well as economic boundary conditions. Within the described systematic methodology, process capabilities are evaluated against different component properties (geometrical variation, workpiece material, etc.) and provide an overview on available technologies for certain designs. The process know-how was gained by shop-floor investigations identifying the process limits (e.g. accessibility). The methodology is explained in the following by means of Blisk/ IBR components.
A Framework for Evaluation of Cyber Security Risks Using Monitoring Data
Authors: Lieuwen Timothy , Perullo Christopher , Kee Jared
Published: September 2023

This paper outlines a process for proactive mitigation measures for detecting and preventing threats through detection of exploited vulnerabilities in power generation assets. In many cases, these vulnerabilities are only known to deep domain experts who are familiar with the intricacies of how these systems work, and not to cybersecurity experts. While a focus on IT security. represents the first line of defense, successful attacks on the OT systems can go beyond disruption to business operations or service and can lead to catastrophic equipment failure. Recent advancements in monitoring and diagnostics technology have been used to protect OT equipment from normal wear and tear but have not been fully operationalized to assist in detecting intrusions.

Monitoring and Diagnostic (M&D) centers typically collect significant sensor data with the aim of detecting faults and failures in operating equipment; however, collection and analysis of additional data including control system settings, verification of sensor signals, and verification of proper actuator function is typically not analyzed. These functions are almost certainly not analyzed from the specific perspective of cybersecurity OT attacks. To help aid in discussions between plant engineers, M&D, and IT/OT, a process and examples are presented for identifying potential attack vectors in the cyber-physical OT systems. This includes a systematic identification of potential systems, categorical attack mechanisms, and cataloguing of the resulting impact.
Analysis of Unsteady Loss Sensitivity to Incidence Angle Variation in Low Pressure Turbine
Authors: Dellacasagrande Matteo , Lengani Davide , Simoni Daniele , Ubaldi Marina , Granata Angelo Alberto , Giovannini Matteo , Rubechini Filippo , Bertini Francesco
Published: September 2023

In the present work, Large Eddy Simulations (LES) of a low pressure turbine cascade have been carried out to understand the different sensitivity to incidence angle variation observed under steady and unsteady inflow conditions. Indeed, experimental evidence shows poor sensitivity to incidence angle variation for the steady case in a range of −9° ≤ i ≤ +9°, while losses grow rapidly in the unsteady flow environment. It will be shown that this is due to wake migration into the core flow region, producing an additional source of losses for the unsteady flow case. Both steady and unsteady simulations have been carried out at nominal and two positive and negative incidence angles.

The LES data have been inspected to identify the physical reasons behind the different loss trends, after being validated by means of blade loading and loss coefficient distributions. To this end, Proper Orthogonal Decomposition (POD) has been applied to each dataset. POD modes clearly identify the different structures responsible for loss production in the steady and the unsteady operation of the cascade. The structures carried by upstream wakes have been isolated and identified both in the boundary layer and in the core flow. The process of bowing, tilting and reorientation of the wake filaments and related structures is shown to be the dominant mechanism responsible for the strong loss sensitivity to the incidence angle variation observed under unsteady inflow. Otherwise, structures responsible for the transition of the blade boundary layer do not exhibit significant variation for both the steady and the unsteady flow cases, thus further strengthening that the sensitivity to incidence variation is mainly due to wake migration into the core flow region. This loss source is not classically considered in literature correlations and actual design processes.
Adapting Artificial Neural Networks Training Algorithms to Adjoint-Based Aerodynamic Shape Optimization
Authors: Gisbert Fernando , Cadrecha David , Quintanal Jaime , Sotillo Adrián , Pueblas Jesús , Serrano Aida , Puente Ricardo , Corral Roque
Published: September 2023

Gradient-based algorithms are one of the pillars of automatic aerodynamic design in the turbomachinery field. Their use is largely extended due to their low computational demand when dealing with hundreds of design variables, especially if gradient computation is performed by means of an adjoint code. Difficulties arise when facing 3D aerodynamic inverse design, trying to obtain automatically a 3D blade geometry that produces a prescribed pressure distribution while fulfilling certain other aerodynamic constraints. Fine-tuning this target pressure distribution along the blade span — with varying fluid conditions along it — generally involves a high number of iterations, making overall automatic design process expensive from a computational point of view.

Many numerical methods have been employed in order to cope with the bad convergence exhibited by basic gradient descent method for ill-conditioned problems: quasi-Newton methods, conjugate gradients, sequential quadratic programming algorithms, among others. However, bad convergence of basic gradient descent method on ill-conditioned problems is not exclusive to 3D aerodynamic inverse design. In the field of artificial intelligence and machine learning, this problem is common when training neural networks.

In order to accelerate the convergence exhibited by gradient descent method on the aforementioned case, this paper makes use of one of the most common adaptive gradient-based methods in the field of neural networks training: Nadam optimizer. Firstly, the principles that allow this method to overcome ill conditioning are explained through Brachistochrone problem example. Secondly, the architecture of this aerodynamic automatic design module is detailed, paying special attention to gradient computation, mesh generation and objective function construction.

Finally, an automatic 3D inverse design of a low-pressure turbine blade, driven by this adaptive step-size algorithm, is performed. The automatic design optimization presented here is carried out in a realistic industrial manner, taking into account different operation conditions in order to mimic human performed design.
Comparing Different Designs of a Grid-Valve for Industrial Steam Turbines
Authors: Bianchini Cosimo , Da Soghe Riccardo , Giannini Lorenzo , Maceli Nicola , Arcangeli Lorenzo , Mariotti Vanessa
Published: September 2023

The current energy market is characterized by the increasing split of energy produced with renewables, and by the strong push towards a sustainable use of the resources and a reduction of the global carbon footprint. Both these two aspects underline the importance of operating the energy production plants in an efficient and effective way not only at full but also at partial load.

This paper presents the results obtained using a CFD commercial code to understand how the different design choices affect the performance of a grid-valve used for steam turbines in the industrial power generation market. Several different configurations were considered, mainly to understand the best trade-off in terms of performance and mechanical aspects. In fact, the grid valves are intended to have a certain modularity and are designed to operate within a given range of conditions and applied to different steam turbine architectures. At best, they should be able to deliver the same performance regardless of the operating conditions or the steam turbine architecture. Therefore, part of the activity focused on the criteria to be used to decide the size the grid valve with respect to the mass flow and the downstream flowpath.

A significant part of the analytical efforts was also devoted to provide a set of rules to account for the performance variability. To this purpose, a significant number of cases was used to cover the most relevant factors affecting the performance of the grid valves. Considered factors include: the variability of the radial length of the stages downstream of the grid valve, the pressure ratio through the grid valve, and the amount of flow extracted upstream of the grid valve.
Experimental Study of Compressible Film Cooling Scaling and Hole Geometry
Authors: Fox Dale W. , Furgeson Michael , Flachs Elise M. , Bogard David G.
Published: September 2023

While modern gas turbine engines operate at hot gas path velocities approaching the speed of sound, few facilities have studied the effects that the flow’s compressibility can have on the adiabatic effectiveness. A new facility at the University of Texas at Austin has been developed to investigate these high Mach number effects and how to appropriately scale laboratory film cooling experiments to engine conditions. This study investigates two film cooling hole geometries, a baseline 7-7-7 shaped film cooling hole and a recent design which has been numerically optimized for increased effectiveness. Both holes are tested at mainstream Mach numbers of 0.25 and 0.50 in a flat plate test section. The optimized hole outperforms the effectiveness of the baseline geometry at all blowing ratios tested, matching the trend in the results of previous studies on these geometries. However, there is a marked decrease in film cooling hole performance as the Mach number is increased.
Comparison of Infrared Spectroscopic Methods in Predicting DCN of Jet Fuels and Their Blends Using Chemometric Tools
Authors: Dalmiya Anandvinod , Sheyyab Manaf , Mayhew Eric K. , Brezinsky Kenneth , Lynch Patrick T.
Published: September 2023

Fuels are made up of thousands of chemical components, but these can be grouped into far fewer chemical functional groups. Fuel properties can be correlated to simpler fuel representations, potentially as simple as the composition of their functional groups. Machine learning (ML) models have been built to predict fuel properties from spectroscopic measurements (preferably in liquid phase). Derived cetane number (DCN) is one such property, which is an indicator of ignition quality in compression-ignition engines. Attenuated total reflectance (ATR) spectroscopy has advantages over transmission-based approaches to overcome challenges associated with the narrow pathlength liquid cells (< 10μm) needed to avoid saturation in strong absorption bands in the mid-infrared. In our previous work, we demonstrated the use of Fourier transform infrared (FTIR) spectra (through transmission) in predicting the DCN of jet fuels after eliminating saturated regions. Convolutional neural network (CNN) models performed the best with a mean percentage error of 3% with an R2 score of 0.931 over a spectral region that includes the fingerprint region. Although those models have shown high predictive capability, since they ignored information from regions likely to show saturated features, it is intuitive that prediction capabilities could be improved further with access to the information in these regions. To evaluate the impact of these saturation regions on DCN estimation, we compare the prediction accuracies and important regions corresponding to DCN obtained from models trained on FT-ATR spectra, which include the regions excluded in the previous work. In this work, uncorrected ATR spectral measurements were used in developing calibration models for predicting DCN of jet fuels and their blends. ATR spectra of jet fuels like F-24, an alcohol-to-jet fuel, Jet-A, etc., and neat hydrocarbons and their mixtures, which in their assembly, represent the chemical functional groups present in jet fuels, were collected using an analytical grade FTIR spectrometer. Spectral measurements between 4000–650cm−1 were used in this analysis, and important spectral regions associated to functional groups correlating to DCN were also identified.
A Strategy for the Design of ORC Multi-Stage Axial Turbines for Geothermal Energy Conversion
Authors: Manfredi Marco , Persico Giacomo , Dossena Vincenzo , Cosi Lorenzo , Forte Annalisa , Arcangeli Lorenzo
Published: September 2023

Geothermal energy is one of the most attractive renewable sources, largely available across US and Europe, but featuring medium-low enthalpy level. Such kind of energy source can be effectively exploited by resorting to Organic Rankine Cycles (ORCs), namely phase-change cycles based on organic fluids, whose thermo-physical properties better match with the low heat grade of the geothermal fluid. Nowadays, ORCs stand out as a mature energy conversion technology, whose performance and tecno-economic optimization greatly rely on the efficiency, reliability, and cost of the turbine. The use of organic compounds implies a peculiar aerodynamic design, where the low specific work and the low speed of sound often lead to turbines featuring one or a few transonic/supersonic stages. For this reason, ORC turbines were historically characterized by lower efficiency and rangeability with respect to steam turbines.

This work presents a strategy to design multi-stage axial turbines for ORC power systems devoted to geothermal energy conversion. Starting from a set of turbine operating conditions, several turbine flow paths are optimized at preliminary level, considering alternative configurations in terms of angular speed, number of stages, and size. A peculiar case study is then investigated in detail, also resorting to throughflow modeling, with the aim of integrating the preliminary sizing with the blade spanwise design. Finally, an assessment of the off-design turbine operation is also presented and discussed, so to characterize the impact of the seasonal variation on the turbine operation and efficiency. Despite the peculiar features of the organic fluids, the systematic optimization of the turbine allows to achieve high performance at both design and off-design conditions.