bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Swirling Flows in Entropy Wave Convection Through High Pressure Turbine Stage
Authors: Pinelli Lorenzo , Marconcini Michele , Pacciani Roberto , Notaristefano Andrea , Gaetani Paolo
Published: October 2022

First stages of aeronautical high-pressure turbines are subjected to significant inlet distortions generated by the combustor system. These disturbances are characterized by velocity and temperature fluctuations convected downstream by the flow. Such perturbations are commonly defined as vorticity and entropy waves and interact with the turbine stages affecting the aerodynamic performance, the heat exchange and generating indirect noise. Moreover, the presence of a swirling flow highly influences the convection and migration of the entropy wave, thus its interaction with the stage. The paper presents an in-depth study of the impact of the swirling flows on the entropy wave evolution by means of experimental campaigns and numerical simulations. Experimental campaigns have been carried out at Politecnico di Milano where a high-pressure turbine rig was equipped with a novel combustor simulator able to generate entropy waves and swirl profiles. Numerical simulations have been performed at the University of Florence by applying time accurate simulation schemes, including incoming disturbances, implemented in the CFD TRAF code. Two different entropy waves (featuring frequencies of 10 and 110 Hz) injected in a counterclockwise swirling region at midspan have been analyzed at two clocking positions: passage aligned and vane aligned. An excellent agreement is found between experimental acquisitions and numerical results: both show an important reduction of the temperature fluctuations through the stage and highlight the effect of the swirling profile on secondary flows and blade wakes. The extensive comparison reported in the paper validates the numerical approach (based on URANS simulations post-processed by a dedicated filtering technique) which has been further applied to study the impact of swirling flows with an opposite rotation (clockwise). The broad numerical investigation combined with the extensive experimental campaign leads to a deeper understanding of the aerodynamic, thermal, and acoustic implications related to entropy wave evolution in a swirling flow highlighting the interaction phenomena and suggesting how to minimize the impact of entropy waves by comparing the results of the different injection positions and swirling flow directions.
Secure Embedded Distributed Control and Instrumentation Architecture for Aircraft Propulsion Systems: Framework, Process, Methods, Challenges, and Opportunities
Authors: Behbahani Alireza R. , Costello John J. , Pakmehr Mehrdad , Skertic Richard J.
Published: October 2022

Cyberattacks on flight control systems could be disastrous. Unlike attacks against classical IT enterprise systems, attacks on flight control systems may influence physical processes and flight dynamics through digital manipulations. These digital manipulations can be catastrophic for safety critical systems such as propulsion and aircraft control systems. Many technical papers and presentations on improving aerospace turbine engine controllers over the last thirty years have explored the transition from a Federated Control System (FCS) to a Distributed Control System (DCS). These distributed architectures offer tremendous benefits for optimized control of gas turbine engines used for commercial and military aerospace platforms. DCS however, suffers from specific vulnerabilities which do not affect classical control systems. The networked architecture of DCS (i.e., communication between its distributed nodes) makes it vulnerable to multiple cybersecurity attack vectors. But this can be an advantage too, if the system is configured and designed properly. The vulnerabilities in the communication network of a safety critical system necessitates the need for the development of appropriate detection and identification techniques for cyber threats. Unfortunately, due to the immaturity of the various required technologies, and the risk mitigation that is typical in the aerospace industry. The transition to a distributed architecture has been slow. In this paper we explore one possible design approach and a framework to develop a more decentralized and distributed control system for gas turbine control. We discuss optimized system control methodologies and review the current state-of-the-art challenges and opportunities for the control system to consider new cybersecurity requirements for hardening the engine control system against vectored threats that could occur during system operation.
Dry Low NOx (DLN) Combustion System Operability Considerations
Authors: Angello Leonard , Noble Bobby , Steele Rob , Cohen Mitch , Emerson Benjamin
Published: October 2022

Modern gas turbines employ dry low NOx (DLN) combustion systems to reduce air pollution and meet stringent environmental regulations. Gas turbine DLN combustion systems operate in lean premix mode near the extinction limit. In this region, the quantity of fuel in the air/fuel mix at the burner is barely sufficient to sustain combustion at low flame temperatures. Safe and reliable operation of modern combustors near the flame extinction limit requires a number of vital elements: 1) an in-depth understanding of mechanisms that promote combustion stability at these extremely low fuel equivalence ratios, 2) precise manufacturing and repair of key combustion components with narrow design tolerances, 3) a reliable monitoring system to detect onset of instabilities in individual combustors, and, 4) protective measures that can implement corrective actions such as changes in fuel splits. Given these elements, operators often need to act proactively in preventing onset of excessive pressure oscillations and combustion-induced vibrations and flame instabilities.

The purpose of this paper is to educate plant engineers on gas turbine combustion systems for operational flexibility of modern gas turbine low-NOx combustion systems. The paper will describe technologies for monitoring, control, and methods for adjusting and optimizing system performance on natural gas fuels. This paper is directed at plant engineers. It presents several applications, with supporting data and photographs, to help this audience understand the core working principles of modern DLN combustion systems.
Reducing Fuel Burn Using SiC/SiC CMC HPT Vanes and Rotor Blades
Authors: Boyle Robert J.
Published: October 2022

Issues with using High Pressure Turbine SiC/SiC CMC vanes and rotor blades for future commercial aircraft engines to reduce fuel burn, and CO2 emissions are explored. The higher temperature capability of SiC/SiC CMC vanes and rotor blades enables higher values of T40 and OPR, which leads to smaller engine cores and lower SFC. Decreasing engine weight, especially for long range flights, can be as significant as decreasing cruise SFC in terms of reduced fuel burn. Specific work increases as T40 increases, and. engine core weight decreases. The work focuses on the first stage vane, and shows that film cooled SiC/SiC vanes are highly desirable. Otherwise, excessive vane thermal stresses are likely. Increases in T40 have accompanied increases in engine OPRs. This leads to small spans in the high pressure components. The effect of decreased spans on blade row efficiency is examined. Cycle analyses are presented which show the effects of changes in blade row efficiency on SFC and specific work.
Combined Cycle, Heat Pump, and Thermal Storage Integration: Techno-Economic Sensitivity to Market and Climatic Conditions Based on a European and United States Assessment
Authors: Vannoni Alberto , Garcia Jose Angel , Guedez Rafael , Sorce Alessandro , Massardo Aristide Fausto
Published: October 2022

The integration of a Heat Pump (HP) with a Combined Cycle Gas Turbine (CCGT) to control the inlet air temperature has been previously investigated turning out to be a promising technology to meet the requirements imposed by the current electricity generation systems in terms of efficiency and flexibility. If the HP is coupled with a Thermal Energy Storage (TES) in an Inlet Conditioning Unit (ICU), it can be exploited in different modes to enhance the off-design CCGT’s efficiency or to boost the power output at full load. Furthermore, fuel-saving would be reflected in avoided emissions. The optimal sizing of the ICU, as well as an accurate estimation of the benefits, is a complex problem influenced by several factors such as the local climate and electricity market prices. The paper aims to systematically investigate, by means of a Mixed Integer Linear Programming model for optimal dispatch, the feasibility of an ICU integration in different scenarios (EU and US), providing general rules for assessing the concept application in new sites all around the globe. Different electricity markets have been analyzed and classified according to the parameters describing the average and variability of prices, the interdependency with the gas market, the ambient temperature, or the local carbon pricing policy. The most favorable conditions are identified and the dependency of the optimal ICU sizing on the climate and the electricity market is highlighted. The concept appears to be highly profitable in the hot regions with high price variability with an NPV of around 60 M€. Additionally, even in less profitable conditions (i.e., stable low prices in a cold climate), the system is able to increase the operating hours and reduce the economic losses. The performances enhancement described does not imply any environmental cost in terms of CO2 emissions.
Evaluation of Adjoint Optimized Hole - Part II: Parameter Effects on Performance
Authors: Yoon Christopher , Gutierrez Daniel , Furgeson Michael T. , Bogard David G.
Published: October 2022

In a previous study from our laboratory, a computational adjoint based optimization method was used to design shaped film cooling holes fed by internal co-flow and cross-flow channels. The associated RANS computations predicted that the holes optimized for use with cross-flow (X-AOpt) and co-flow (Co-AOpt) would increase adiabatic effectiveness significantly compared to a baseline 7-7-7 shaped hole. Experimental validations of these performance predictions are presented in companion paper (Gutierrez et al., 2022). Although the experimental values were significantly lower than the computational predictions, the adiabatic effectiveness for the adjoint optimized holes was measured to be noticeably higher than that for the baseline 7-7-7 shaped hole. Specifically, the X-AOpt hole was 75% higher and the Co-AOpt hole was 30% higher in terms of peak performance when P/D effects were accounted for. In this study, the effects of various key parameters on the performance of the adjoint optimized holes were determined. For these experiments the internal channel velocity ratios ranged from VRc = 0.2 to 0.4, both co-flow and counter-flow conditions were used, and the density ratio ranged from DR = 1.2 to 1.8. These provided a quantification of the performance of the adjoint optimized holes over a wide range of operating conditions encompassing engine relevant conditions. Adiabatic film effectiveness measurements and thermal field measurements are made to understand the performance variations and to compare with 7-7-7 SI (sharp inlet).
A Study of Stall Process in an Axial Flow Compressor With Foam Metal Casing Treatment
Authors: Li Jia , Sun Dakun , Xu Ruize , Dong Xu , Sun Xiaofeng
Published: October 2022

Recently, a kind of foam metal casing treatment (FMCT) was proposed and tested in a low-speed axial compressor. It was found that the FMCT performed well in both stall margin improvement and noise emission reduction of the compressor. The result is beneficial to the future advanced turbofan design. As a companion research, the goal of this paper is to give insight into the inner working mechanism of the FMCT in terms of unsteady pressure signal analysis across a range of operating points. The investigation is focus on pre-stall behavior of the compressor with/without the FMCT. Pressure measurements using high frequency response sensors have been carried out on the compressor to capture pre-stall process and interpret the flow structure in the blade tip region. A particular emphasis is given on the flow patterns present in the tip region and how they evolve in different casing wall conditions. The results show two different stall inception behavior throughout the throttling process. The compressor with the foam metal placed at the rotor mid-chord experiences a long-length-scale stall precursor. With smooth casing and the foam metal placed near the rotor leading edge, the compressor shows a short-length-scale stall precursor. The relevance of results obtained and possible mechanism involved are also analyzed and discussed at last.
Numerical Investigation of Loss Mechanisms in a Partially Loaded Supersonic ORC Axial Turbine Stage
Authors: Ziaja Karl , Post Pascal , Schramm Andreas , Willers Ole , Seume Joerg R. , di Mare Francesca
Published: October 2022

Industrial processes, small-scale power plants or internal combustion engines produce a high amount of waste heat as a by-product. The Organic Rankine Cycle (ORC) technology allows to recover that heat more efficiently compared to steam/water in conventional Clausius-Rankine cycles. For a comparably efficient and economical operation over a wide range of operating conditions, partial admission control appears to be a well-suited design option for ORC turbines. However, accurate numerical performance prediction of a partial admitted turbine stage is challenging and requires full annulus CFD computations of the partial admitted turbine stage.

In the present study, a comprehensive analysis of the internal flow and aerodynamic loss mechanisms in a supersonic, axial single stage impulse 18.3 kW ORC turbine operating with an ethanol/water gas-mixture as working fluid at a partial admission ratio of 40 % based on steady-state CFD computations is presented. A comparison of numerical and experimental results for a partial admission ratio of 20 % and 40 % shows, that for a partial admission ratio of 40 % efficiency predictions based on steady-state simulations are within the measurement uncertainty. To extract and quantify the magnitude of the occurring loss mechanisms, the entropy generation rate is analysed. The results show an entropy generation between the rotor blades and the closed stator passages, which has a significant influence on the turbine performance and leads to a reduction of efficiency of about 2 to 4.5 ppt. This was found to be related to a strong jet induced in the narrow gaps between the rotor leading edges and the trailing edges of the closed stator passages, which mixes with the stagnant flow in the following nozzle sections.
Highly Time Resolved, Combined Temperature and Heat Flux Measurement Technique Based on ALTP Sensors
Authors: Huber Konstantin , Rödiger Tim
Published: October 2022

This study demonstrates a new methodology for the simultaneous direct measurement of temperature and heat flux within the same sensing element of heat-flux sensors. The methodology is demonstrated for fast response ALTP-sensors and makes use of a temperature-resistance correlation. The new methodology enables an inherent comparison and validation of the heat flux density signal of ALTPs. Good agreement is found based on experiments in the stagnation point of a subsonic hot air jet. The results of the mainly convective heat flux densities are compared against a standard coaxial thermocouple indicating good agreement of mean values and signal characteristics. The simultaneous direct measurement of the temperature and heat flux allows the time resolved calculation of local heat transfer coefficients and Nusselt numbers. The spectral analysis of the Nusselt number exhibits an excellent signal-to-noise ratio.
Deformation and Damage Behavior of a 1 Cr-Cast Steel Under Multiaxial Loading at Elevated Temperatures
Authors: Kontermann Christian , Erbe Alexander , Conrad Fabian , Kraemer Karl Michael , Oechsner Matthias
Published: October 2022

Rising demands on material performance at high temperature in components under complex loading such as steam- and gas turbine housings require an increase in versatility and precision of component life modelling approaches. However, the database to calibrate those models is commonly derived from uniaxial testing. The impact of multiaxial loading, both proportional and non-proportional, is usually addressed theoretically by the use of equivalent stress/strain formulations or reduction ratios derived from few specific validation tests.

Therefore, a research program which systematically investigates the fatigue life of a 1Cr-cast steel both experimentally and theoretically has been initiated recently. For the experimental part, cruciform specimens are tested in a servo-hydraulic biaxial test rig equipped with an induction heating device. Each experiment is accompanied with finite element simulations before and after the test to parametrize the loading condition and derive equivalent loading parameters at hot-spot locations.

When assessing cycles until crack initiation in the experiments using the von Mises equivalent strain range, a reoccurring sequence in the impact of the axis ratio can be observed. Beside the fatigue life in terms of cycles to crack initiation, the multiaxial loading conditions may also affect the deformation behaviour, in detail cyclic softening. Such effects are discussed by comparing the produced experimental evidence with results gained from a unified constitutive material model. Furthermore, different lifetime parameters are applied in order to judge their accuracy and suitability for design applications.
Waste Heat Recovery Driven Turbocharger System for Gas Turbine
Authors: Sammak Majed , Jupudi Maruthi , Dawood Alaaeldin , Khalidi Abdurrahman
Published: October 2022

This paper introduces a novel concept for power augmentation by waste heat recovery turbocharger system. The turbocharger system, coupled to an external air compressor, is driven by the exhaust gases waste heat. The air compressor then compresses additional air that will be injected into the gas turbine compressor discharge and boost the gas turbine power. As the heat recovery system drives the turbocharger with heat recovered from the exhaust gas stream, the power produced by the power generation system increases without decreasing the efficiency.

Compressed air injection helps with resorting the missing gas turbine compressor air at high ambient temperatures and thus the compressed air injection is more suitable for gas turbines operating at hot ambient conditions. The paper also investigates utilizing the waste heat recovery turbocharger system at gas turbine part load operation for fuel saving and heat rate improvements.

This paper analyzes the gas turbine simple cycle power improvements at different ambient conditions and compressed air injection percentage. The gas turbine power proved to increase by around 2% at 1% air injection and 10% at 5% air injection at high ambient temperatures 30°C, 40°C and 50°C. Furthermore, the gas turbine heat rate improvement landed at 6.5% at 50°C and 5% air injection.

This study also compares the waste heat recovery system with other power augmentation technologies, namely the inlet mechanical chiller and the evaporative cooler.

Compared to a gas turbine with waste heat recovery turbocharger air injection system at 5% air injection, the electrical chiller system increases the gas turbine heat rate by around 2% assuming chiller COP of 5.

The waste heat recovery turbocharger system offers both power augmentation and heat rate improvements for simple cycle gas turbines. Additionally, this system can extend the hot gas path life by lowering the firing temperature without losing power.
Analysis of Turbomachinery Averaging Techniques
Authors: Frey Christian , Ashcroft Graham , Müller Michael , Wellner Jens
Published: October 2022

In this paper, various averaging techniques commonly used in turbomachinery applications are analyzed. It is shown how the work average relates to Miller’s mechanical work potential and that it is, in a certain way, consistent with Hartsel’s cooled turbine efficiency. It is found that a key to understand these approaches is to analyze the impact that entropy variations at inflows have on them.

Second-order asymptotics of mixing entropy are used to establish a close relationship between flux and work averages. It is found that the mixing entropy asymptotic due to entropy modes is identical for both averages. The work average, along with Miller’s mechanical work potential analysis, is as optimistic as the entropy average for vorticity and acoustic modes, but as pessimistic as the flux averaging for entropy variations. This explains why mechanical work potential based analysis is pessimistic about the inflow and thus optimistic about the efficiency of a turbine for high entropy variations in the inflow, e.g. in the presence of hot streaks or film cooling.

Radial averaging techniques are discussed and their impact on turbine performance is shown. Our findings are illustrated by means of the analysis of steady and unsteady flow simulations of a 1.5 stage turbine configuration.
Crosswind Aerodynamic Analysis Using Quasi 3D Ducts
Authors: Sarvankar Sumit Shankar , Issai Arasu Adrin , Vadlamani Nagabhushana Rao
Published: October 2022

In this paper, we address the aerodynamics of the nacelle subjected to severe crosswinds. A series of numerical simulations are carried out on a Quasi 3D duct which has been extracted from a 3D axisymmetric nacelle. The operating characteristics of the Q3D duct, total pressure profiles at fan-face and isentropic Mach number distributions over the intake lip, are demonstrated to be in encouraging agreement with the experiments. Some of the strategies to predict two different types of hysteresis which are either observed at low mass flow rates or at lower operating pressures within the duct (and hence at low Reynolds numbers) are discussed. Contrasting trends in the turbulent kinetic energy predictions of k-ω and γ-Reθ models at low system pressures are observed, which indicate that the boundary layers on the windward side of the intake lip are transitional. Finally, we discuss the possibilities of improving the off-design nacelle performance using active plasma flow control. While a low-speed separation can be eliminated using plasma actuator, controlling high speed separation remains a challenging task.
Acoustic Signature of Flow Instabilities Present in Industrial Centrifugal Compressor
Authors: Liskiewicz Grzegorz , Jaeschke Andrzej , Kryłłowicz Władysław
Published: October 2022

In this paper the possibility of diagnosing the compressor flow stability by acoustic measurements is explored. A correlated acoustic signal was measured together with pressure in the flow channel. The method allowed to evaluate the applicability of acoustic measurements for simple diagnostics of machine working conditions. The advantage of acoustic study is that it can be conducted ad-hoc without installing any special equipment, does not interfere with the machine setting and does not require changing the working conditions. The biggest downside is the method accuracy, possible reflections and interference with the noise coming from another machines present in the room. Study was performed on a low speed industrial compressor. A set of acoustic measurements was conducted in 7 locations to observe the influence of possible reflections. Study included continuous voice recording made at constant flow conditions and signals gathered during continuous closure of the throttling valve - on the way to the surge. Study confirmed that the microphone noise measurement allows to distinguish the main unstable flow phenomena. It could be potentially used as an initial test of flow stability in industrial centrifugal compressor or even predict the surge proximity.
Rotor37 Aerodynamic Optimization: A Machine Learning Approach
Authors: Beqiraj Klajdi , Perrone Andrea , Sanguineti Marco , Ratto Luca , Ricci Gianluca
Published: October 2022

The present paper presents an enhanced method for aerodynamic optimization of NASA Rotor37 row based on Machine Learning (ML) algorithms. An aerodynamic database has been developed using a commercial 3D (three dimensional) computational fluid dynamics (CFD) solver; a RANS (Reynold Averaged Navier Stokes) steady approach with a two-equation SST (Shear Stress Transport) model has been adopted for the aerodynamic computations.

The database geometries have been parametrized through autoencoders with the aim of automatically extracting characteristic geometric features and obtaining extensive parameterization of the blade. Autoencoders are a specific type of Neural Network which allow to feed non-parametric CAD designs into ML models. The autoencoder latent parameters describe the blade 3D geometry and can be used as an alternative to the standard geometric parameters in describing the shape of each sample. The main advantage is that autoencoders enable an automatic parameterization of 3D geometries, thus overcoming the limits imposed by manual parameterization.

A Neural Network has been used in order to predict global performance (e.g., pressure ratio, efficiency) and 3D field quantities (pressure and temperature distribution).

The optimization through reinforcement learning algorithms has been carried out in order to maximize the blade efficiency; geometries have been generated by exploiting the latent parameterization obtained by autoencoder. The accuracy of the ML algorithm forecast has been evaluated through CFD simulations carried out on the optimal sample. The results related to the optimized sample have been presented and highlight all the benefits of the proposed approach.
Experimental Investigation of a High-Speed Turbine With Rainbow Rotor and Rim Seal Purge Flow
Authors: Cernat Bogdan , Pinho Jorge , Okada Mizuki , Lavagnoli Sergio
Published: October 2022

The present paper addresses the experimental and numerical study of the unsteady flow established in a high-pressure turbine stage with rim seal purge. The HPT test section, operated at engine-relevant flow conditions in the high-speed turbine rig of the von Karman Institute, is heavily instrumented for high-resolution, high-bandwidth aerothermal measurements. A rainbow rotor setup allows the simultaneous testing of six different sectors, each hosting a specific tip and platform geometry optimized for enhanced aerodynamic performance. This paper focuses on the flow over the baseline sector, equipped with an axisymmetric hub platform and a squealer tip, with a purge flow rate matching 1.74% and 1% of the stage mass flow. The numerical study relies on Reynolds-averaged Navier Stokes computations with test-calibrated boundary conditions.

Unsteady pressure and heat transfer measurements are performed at the rotor shroud. The maximum heat transfer is achieved along the front pressure side rim, whereas the squealer cavity generates a region of uniformly low static pressure and heat flux. The experimental adiabatic wall temperature is derived to quantify the thermal contribution to the global heat flux, demonstrating an increase in over-tip gas temperature up to 1.2 T01 above the pressure side rim. A Euler-based model is proposed to evaluate the temperature-driving work-exchange mechanism in the tip gap. The peak in casing heat transfer coefficient (750 W/m2) is found at the tip leading edge.

Time-resolved measurements of outlet total pressure, Mach number, and flow angle confirm the predicted phase and intensity of the tip leakage and upper passage vortex in the near-casing region. At 20% hr, the total pressure minimum is highly under-predicted by the RANS, indicating an inaccurate modeling of the interaction between rim seal purge and main flow. The measured impact of the purge flow variation is more significant than predicted by the RANS computations, with a negative offset of about 0.5% P01 in the lower 50% hr at lower purge flow rate.
Effects of Turbine Conditions on Rim Seal Performance and Prediction
Authors: Burden Shaun , Chew John W. , Gao Feng , Marxen Olaf
Published: October 2022

Predicting the degree of hot gas ingestion into turbine disc cavities is a challenge for computational fluid dynamics due to the complex unsteady flow dynamics in turbine rim seals and sensitivity to operating condition and seal geometry. This paper reports research aimed at clarifying the effect of operating conditions on seal performance and turbulence modelling requirements. A systematic study of sealing performance for an axial rim seal is reported, comparing an unsteady Reynolds-averaged Navier-Stokes (URANS) model and wall-modelled large-eddy simulation (WMLES). The conditions considered are classed as rotation-driven ingestion, pressure-driven ingestion, and combined mechanism ingestion. WMLES and URANS results showed similar ingestion levels and seal flows within the pressure-driven regime. For the rotationally-driven condition URANS displays larger, more coherent vortical flow structures than the WMLES. The larger vortices in the URANS drive ingress into the wheel-space resulting in higher levels of ingestion than indicated by the WMLES. For the combined ingestion condition, WMLES shows higher levels of ingestion and flow unsteadiness than URANS. The present results give some explanation for the mixed results reported for the performance of URANS models in previous studies.
Mooring System Design and Analysis for a Floating Offshore Wind Turbine in Pantelleria
Authors: Ghigo Alberto , Niosi Francesco , Paduano Bruno , Bracco Giovanni , Mattiazzo Giuliana
Published: October 2022

The mooring system plays a key role in a floating offshore wind turbine: it connects the floating structure to its anchor on the seabed and it is designed to prevent the platform from drifting under the action of wind, waves and currents. The layout of the mooring system is strictly connected to the installation site: in the first place it depends on the bathymetry and the type of seabed which conditions the type of anchor that can be used; secondly by the wind and waves loads in extreme sea states.

To properly design the mooring system, three different configurations are proposed and discussed, respectively adapting catenary, taut leg and semi-taut methodologies for a floating offshore wind turbine located near the island of Pantelleria, in Sicily. For each configuration, the Hexafloat foundation, developed by Saipem, is considered. Important design constraints such as how large the nominal sizes are, how long the mooring lines are, how far the anchor points are located, are demonstrated in detail. The material used will range from steel chains and wires to polyester ropes, to grant economically viable solutions.
A New Health Evaluation Approach for Gas Turbine Using Its Component Performance Parameters
Authors: Luan Junqi , Cao Yunpeng , Ao Ran , Han Xiaoyu , Li Shuying
Published: October 2022

Nonlinear gas path analysis (NGPA) is an important method for gas path fault diagnosis, and it is also the main technology for component performance estimation of gas turbine engines. However, the solution speed of the nonlinear gas path model is difficult to meet the time requirements of realtime performance evaluation due to the strong nonlinearity of the gas turbine model. In response to this problem, this paper proposes a new approach to gas turbine health evaluation based on component performance parameters. A nonlinear gas path model is established to realize the offline estimation of the performance parameters of the gas turbine components. The general regression neural network (GRNN) is introduced to realize the mapping between the operating data of the compressor wash cycle and the performance parameters of the components. The dimension of component performance parameters was reduced by principal component analysis (PCA) to extract degraded features by simplifying the complexity of the evaluation, and the health value (HV) is proposed to characterize the gas turbine health status. A health evaluation testing for the marine gas turbine was carried out. Compared with the NGPA method, the maximum average absolute percentage error, and root mean square error of the component performance parameters estimated by the proposed method are 0.384% and 0.336, respectively. The testing results show that the proposed method can estimate the component performance parameters of the gas turbine online, and realizes the evaluation of the health status of the gas turbine.
Establishing a Generic Stress-Life Framework for Single-Crystal Nickel-Base Superalloys
Authors: Irmak Firat , Karim Sahil , O’Nora Nathan , Gordon Ali P.
Published: October 2022

Selection of materials to be used for components experiencing extreme conditions is a critical process in the design phase. Nickel-base superalloys have been frequently used for hot gas path components in the turbomachinery industry. These components are required to withstand both fatigue and creep at extreme temperatures during their service time. In general, the extreme temperature materials mostly embody polycrystalline, directionally solidified, and single crystal superalloys. Single crystallization has been utilized with nickel-base superalloys since 1980s. This method forms one grain by eliminating all of the grain boundaries, which has resulted with thermal, fatigue and creep properties superior to conventional alloys. It is essential for design engineers to predict accurate damage behavior and lifespan for these components to prevent catastrophic failures. This study presents generic elastic and stress-life models for single crystal nickel-base superalloys based on observed trends. Despite the development of over 50 variations of single crystal Nickel-base superalloys, the behavior of these alloys nominally follows similar mechanical behavior trends with respect to temperature and orientation. Temperature-, rate-, and orientation-dependence of these materials are studied. In this study, [001], [011] and [111] orientations are mainly considered. The goal is to eliminate extensive time and cost of experiments by creating parameters to be used in life calculations for generic single crystal alloys. While the stress-based approach to fatigue analysis of materials was the first to be developed, it continues to endure with broad usage in a wide variety of engineering applications. These models tend to be used for the cases with high number of cycles to failure behavior or called high-cycle fatigue (HCF) conditions. In this work, the total damage is divided into two different modules; fatigue and creep damages. Miner’s Rule is utilized to combine these modules. Models which can predict the cycles to failure data with the most usage-like conditions and require least amount of data are preferred. Parameters for the models are built on regression fits in comparison with a comprehensive material database. This database includes elastic, plastic, creep, and fatigue properties.
Techno-Economic Comparison of Supercritical CO2, Steam, and ORC Cycles for WHR Applications
Authors: Baglietto Giovanni , Maccarini Simone , Traverso Alberto , Bruttini Paolo
Published: October 2022

Supercritical CO2 (sCO2) is taking a growing interest in both industry and academic communities as a promising technology capable of high efficiency, flexibility, and competitive capital costs. Many possible applications are studied in the energy field, from nuclear power plants to CSP and waste heat recovery (WHR).

To evaluate the competitiveness of sCO2 cycles relative to other competing technologies, mainly steam and ORC, a specific techno-economic analysis is needed to fairly compare the different technologies for each application, in order to find the most appropriate market position of the innovative sCO2 plants, compared to the existing steam and ORC solutions.

In the present study, techno-economic analysis and optimization have been conducted focusing on WHR applications, for different sizes and cycle parameters operating conditions using an in-house simulation tool. The analyzed cycles were first optimized by aiming at maximizing the net electrical power and then aiming at minimizing the specific capital cost. As a result, compared to traditional plants, we obtained that in the first case, the more complex sCO2 cycle configuration shows competitive performance, while in the second case, the simpler sCO2 cycle configuration has a lower specific cost for the same electrical power produced (with a difference of approximately −130 €/kW compared to the steam cycle). In general, while traditional technologies confirmed a good trade-off between performance and cost, supercritical CO2 cycles show attractive characteristics for applications requiring simplicity and compactness, guaranteeing in the meantime other technical advantages such as water-free operation.
ICME Computational Framework for Ceramic APS Coatings
Authors: Abdi Frank , Achanta Surekha , Baid Harsh , Harik Vasyl , Yaghmaie Reza , Morscher Gregory N. , Balint Daniel , Zawada Larry , Jefferson George
Published: October 2022

Integrated Computational Material Engineering (ICME) framework for Air Plasma Spray (APS) process for ceramic coatings is developed for optimizing multifunctional coatings and APS process for Thermal Barrier Coating (TBC) system. ICME simulations of APS process for TBC, the burner rig test and furnace test of TBC have been performed along with the test validation of ICME predictions for Yttria-stabilized-zirconia (YSZ) TBC with APS 8YSZ top coating with / NiCoCrAlY bond over Waspaloy substrate. ICME predictions for residual deflection of TBC due to thermal loads after APS process, burner rig test and furnace test are in close agreement with the test results. Both test and ICME predictions show the as-manufactured TBC specimens exhibit bending after APS process and bending after Burner Rig and Furnace testing. Finite element model for TBC specimens shows bending induced by APS process, its thermal gradients and residual thermal stress. Microscale thermal models for APS process, burner rig test and furnace test have been used to predict thermal processes, porosity and stresses. Rumpling analysis of TBC predicts rumpling amplitude due to thermal stresses and thermal oxidation growth (TGO) in TBC, thickness of TGO, bond stress during rumpling and stresses in TGO layer. Predictions for the thickness of TGO compares well with experimental data. Progressive damage analysis revealed that failure is due to tension and out of plane shear, delamination growth due to oxidation penetrating YSZ TBC from the bond.
Near Critical Point Testing and Performance Results of a sCO2 Compressor for a 10MWe Brayton Cycle
Authors: Pelton Robert , Bygrave Jon , Wygant Karl , Wilkes Jason , Revak Thomas , Kim Kilyoung
Published: October 2022

Development and commercial acceptance of sCO2 Brayton cycles for power generation applications are growing rapidly as they offer performance advantages over other cycles. To maximize the cycle performance, the compressors are designed to operate near the critical point of the working fluid. At the critical point the fluid properties change rapidly with variations in inlet conditions. This makes it challenging to both accurately predict the performance and guarantee the operability of the compressor, as the behavior is affected by these slight variations in inlet conditions. A full scale 1st stage main compressor for a 10MWe-Class recompression Brayton cycle was built and tested to validate performance and operability in this unique operating range.

The compressor was tested in a laboratory environment with additional instrumentation, beyond what is required by PTC-10, to minimize the uncertainty in the measured performance. Complete constant speed characteristics were collected at multiple supercritical points, operating at constant inlet conditions for each speed line covering a range of compressor inlet densities from 400 to 600 kg/m3. Variations in the compressor stage efficiency and choke margin were observed, and the overall operability and stability of the compressor in response to changes in operating condition were also monitored. The compressor was shown to have excellent performance that closely matched the original design prediction. The performance at various inlet conditions showed minimal change in isentropic head coefficient at the design flow, but did show some variation in efficiency and choke margin across the map. These changes in performance were observed to be minimal, and did not affect the stable operation of the compressor. The results demonstrate that a commercial scale sCO2 compressor can operate near the critical point and achieve the high levels of performance and stability required for power generation applications.
Experimental Investigation of Flame-Film Cooling Interactions With an Academic Test Rig and Optical Laser Diagnostics
Authors: Petit Sylvain , Quevreux Benjamin , Morin Romain , Guillot Romain , Grisch Frédéric , Xavier Pradip
Published: October 2022

The development of lighter low-carbon technologies in the aviation sector raises a technological challenge regarding material durability and wall thermal management. This study aims to introduce a new optically accessible test rig to investigate the interaction between a premixed CH4/air turbulent flame and a parietal cooling air film for various blowing ratios. Laser Doppler velocimetry (LDV) is implemented to measure the cooling air and the mainstream inflow conditions. The impact of the blowing ratio on the mean flame topology is conducted with OH* chemiluminescence. Results show that the flame-wall distance increases with the blowing ratio and eventually reach a plateau, while the flame length constantly decreases. OH Planar-laser induced fluorescence (OH-PLIF) and phosphor thermometry (PT) are performed to assess the near-wall flame structure and the cooling effectiveness. The flame seems to be aerodynamically controlled while the cooled-air momentum has a beneficial impact on the wall temperature.
Numerical Investigation of the Local Thermo-Chemical State in a Thermo-Acoustically Unstable Dual Swirl Gas Turbine Model Combustor
Authors: Karpowski T. Jeremy P. , Ferraro Federica , Steinhausen Matthias , Popp Sebastian , Arndt Christoph M. , Kraus Christian , Bockhorn Henning , Meier Wolfgang , Hasse Christian
Published: October 2022

In this work, the thermo-acoustic instabilities of a gas turbine model combustor, the so-called SFB606 combustor, are numerically investigated using Large Eddy Simulation (LES) combined with tabulated chemistry and Artificial Thickened Flame (ATF) approach. The main focus is a detailed analysis of the thermo-acoustic cycle and the accompanied equivalence ratio oscillations and their associated convective time delay. In particular, the variations of the thermo-chemical state and flame characteristics over the thermo-acoustic cycle are investigated. For the operating point flame B (Pth = 25kW, Φ = 0.7), the burner exhibits thermo-acoustic instabilities with a dominant frequency of 392 Hz, the acoustic eigenmode of the inner air inlet duct. These oscillations are accompanied by an equivalence ratio oscillation, which exhibits a convective time delay between the injection in the inner swirler and the flame zone. Two LES, one adiabatic and one accounting for heat losses at the walls by prescribing the wall temperatures from experimental data and Conjugated Heat Transfer (CHT) simulations, are conducted. Results with the enthalpy-dependent table are found to predict the time-averaged flow field in terms of velocity, major species, and temperature with higher accuracy than in the adiabatic case. Further, they indicate, that heat losses should be accounted for to correctly predict the flame position. Subsequently, the thermo-chemical state variations over the thermo-acoustic cycle for the enthalpy-dependant case are analyzed in detail and compared with experimental data in terms of phase-conditioned averaged profiles and conditional averages. An overall good prediction is observed, although an overestimation of the oscillation amplitude yields a slight over-prediction of the velocity field in the low-pressure phases. The results provide a detailed quantitative analysis of the thermo-acoustic feedback mechanism of this burner.
Power Flow Optimization for a Hybrid-Electric Propulsion System
Authors: Papadopoulos Konstantinos I. , Nasoulis Christos P. , Ntouvelos Elissaios G. , Gkoutzamanis Vasilis G. , Kalfas Anestis I.
Published: October 2022

The present study deals with the optimization of performance for a hybrid-electric propulsion system. It focuses on the modeling and power management frameworks, while evaluation is done on a single flight basis. The main objective is to extract the maximum out of the novel powertrain archetype. Two hybridization factors are considered. The pair helps to describe the degree of hybridization at the power supply and power consumption levels. Their revised mathematical definition facilitates a unique method of hybrid-electric propulsion system modeling, that maximizes the conveyed amount of information. An in-house computational tool is developed. It employs a genetic algorithm optimizer in the interest of managing power usage during flight. Energy consumption is set as the objective function. The operation of a 19-seater, commuter aircraft is investigated. Turbo-electric, series-hybrid, parallel-hybrid and series-parallel variants are derived from a generic composition. An analysis on their optimized performance, with different technological readiness levels for 2020 and 2035, is aimed at identifying where each system performs best. Considering 2020 technology, it does not yield a viable hybrid-electric configuration, without suffering significant payload penalties. Architectures relying on mechanical propulsors show promise of 15% reduction to energy consumption, accounting for 2035 readiness levels. The concepts of Boundary Layer Ingestion and Distributed Propulsion display the potential to boost electrified propulsion. The series-hybrid and series-parallel configurations are the primary beneficiaries of these concepts, displaying up to 30% reduction in fuel and 20% reduction in energy consumption.
Impacts of the Additive Manufacturing Process on the Roughness of Engine Scale Vanes and Cooling Channels
Authors: Wildgoose Alexander J. , Thole Karen A. , Subramanian Ramesh , Kersting Lisa , Kulkarni Anand
Published: October 2022

By leveraging the additive manufacturing platform, development time and costs for turbine component testing can be reduced relative to traditional investment casting. Surface roughness is a key characteristic of the additive manufacturing process that can impact flow, heat transfer, and mechanical integrity of printed components. There are multiple design and build considerations that result in variability in surface roughness especially when additively fabricating complicated three-dimensional vanes and internal cooling passages. This study characterizes the surface roughness of internal cooling passages, vanes, and flat external surface samples made using additive manufacturing, specifically the direct metal laser sintering process. The samples were manufactured with various wall thicknesses, layer thicknesses, build locations, build directions, and on different AM machines. A combination of computed tomography scanning and optical profilometry were used to evaluate surface roughness levels. The data indicates that the dominate factors in roughness for a given layer thickness are a function of wall thickness, build location, and build direction.