bluuebunny/crossref_metadata_2025_split huggingface dataset:
Full Rejuvenation Heat Treatment of MGA 1400DS
Authors: van Esch Hans , Pietersen Stijn , Greaves Wayne , Bridges Alex , Scheibel John 
Published: September 2023

Abstract
Directionally Solidified (DS) nickel-base superalloys have been extensively used for power generation turbine blades. These blades are exposed to high stresses and temperatures for extended periods of time and aging the microstructural and reducing the mechanical properties. After an operational cycle a repair is typically performed to restore dimensional and coating integrity as well as restore metallurgical and mechanical properties of the base material to extend the life of components manufactured from DS alloys. These repair methods can include heat treatments for stress relieving weldment, application of braze, coatings and rejuvenation of the aged base material. Industry standard heat treatments (ISHT) for these DS alloys do not always provide a (full) rejuvenation. Therefore TEServices, Sulzer and EPRI improved ISHT for DS alloys, such as MGA 1400DS and GTD 111DS, for obtaining a full rejuvenation these base materials and obtaining metallurgical and mechanical properties that, in some cases, exceeds the new material properties [1].
The study in this paper focuses on modifying MGA 1400DS ISHT to obtain a full rejuvenation (solutioning the gamma prime during solution heat treatment in the dendritic and inter-dendritic regions) without negatively impacting the metallurgical structure (such as incipient melting) and mechanical properties. This study was performed using optical and scanning electron microscopy evaluating the microstructure of MGA 1400DS in as new, artificially aged and heat treated condition to establish the impact of full rejuvenation heat treatment (FRHT). Mechanical testing was performed on new, aged and FRHT MGA 1400DS to establish the impact of aging and FRHT compared to new material. For this, creep and stress rupture, fatigue, and combination of stress rupture and fatigue testing was performed.
The findings in this study show that FRHT provides superior metallurgical and mechanical properties of MGA 1400DS when compared to new and aged material.
Damping and Stiffness Mistuning Effects in a Bladed Disk With Varied Disk Coupling
Authors: Krizak Troy , Kurstak Eric , D’Souza Kiran 
Published: September 2023

Abstract
Component mode mistuning (CMM) is a well-known, well documented reduced order modeling technique that effectively models small variations in blade-to-blade stiffness for bladed disks. In practice, bladed disks always have variations, referred to as mistuning, and are a focus of a large amount of research. One element that is commonly ignored from small mistuning implementations is the variation within the blade-to-blade damping values. This work seeks to better understand the effects of damping mistuning by utilizing both structural and proportional damping formulations. This work builds from previous work that implemented structural damping mistuning reduced order models formulated based on CMM. A similar derivation was used to create reduced order models with a proportional damping formulation. The damping and stiffness mistuning values investigated in this study were derived using measured blade natural frequencies and damping ratios from high-speed rotating experiments on freestanding blades. The two separate damping formulations that are presented give very similar results, enabling the user to select their preferred method for a given application. A key parameter investigated in this work is the significance of blade-to-blade coupling. The blade-to-blade coupling study investigates how the level of coupling impacts damping mistuning effects versus applying average damping to the bladed disk model. Also, the interaction of stiffness and damping mistuning is studied. Monte Carlo simulations were carried out to determine the amplification factors, the ratio of mistuned blade responses to tuned blade responses, for various mistuning levels and patterns. The baseline parameters were chosen to match an actual bladed disk tested in a rotating experimental rig.
Reduced-Order Model of Aero-Thermal-Mechanical Interactions in Ultra High-Speed Micro Gas Turbines
Authors: Tiralap Aniwat , Tan Choon S. 
Published: September 2023

Abstract
Ultra high-speed micro gas turbine engines developed for high performance could experience substantial thermal-induced effects on engine operation due to high temperature gradients relative to those in conventional large gas turbine engines. A reduced-order model for quantifying thermal-induced differential expansion of the shaft-bearing housing system is developed based on insights obtained from unsteady computations. The key controlling non-dimensional parameters characterizing the aerothermal-mechanical interaction and response are identified using the reduced-order model that yields thermal-induced mechanical deformation in agreement with the computed results. For geometrically similar engine systems, the controlling non-dimensional thermal and structural parameters consist of: (1) shaft fin parameter, (2) housing fin parameter, (3) ratio of heat diffusivity of housing to that of shaft, (4) 3 cooling flow parameters, and (5) ratio of coefficient of thermal expansion of the housing to that of shaft. These non-dimensional parameters serve as a guideline for developing strategies for controlling bearing clearance variation within the acceptable margin, including selecting shaft and housing materials with appropriate properties as well as tailoring the cooling flow. An approximate scaling rule for thermal-induced shaft-bearing housing clearance variation in engines of various sizing is formulated; specifically, the rule provides a direct means for estimating the time instant and the design attributes under which a specific value of minimum shaft-bearing clearance would occur during the engine start-up process to steady-state operation. A design example is provided to illustrate that adjustment of thermal and structural characteristics through thermal conductivity and coefficient of thermal expansion of the housing material is adequate to mitigate the thermal expansion mismatch issue without engine structure redesign.
Aerodynamic Impact of Secondary Air Injection Flowrates on the Main Annulus Flow Field and Performance for a Transonic High-Pressure Turbine Stage
Authors: Okita Yoji , Kazawa Junichi , Fuchigami Kazutaka , Yamane Takashi , Tanaka Nozomi , Sato Hiroki , Hamabe Masaaki , Tanimitsu Haruyuki 
Published: September 2023

Abstract
In this study, the influence of secondary air blowing on the main annulus flow field and performance of a transonic high-pressure turbine (HPT) was investigated experimentally and numerically.
The experimental setup was a single-stage, unshrouded turbine with a blading consistent with modern HPTs. The entire testing campaign was conducted in a full annular, rotating, continuous turbine test rig at the Japan Aerospace Exploration Agency (JAXA), which realized the most faithful matching unrivalled of both the primary and secondary stream similarity parameters to reality. An elaborate secondary air system implemented in the hardware enabled it to mimic all the dominant coolant/purge streams representative of advanced hot sections: the full coverage film-cooling on stator and rotor airfoils, disk wheelspace purge air blown forward and aft of the rotor, and coolant injection through the over-tip casing. Detailed three-dimensional flow field and efficiency measurements for various secondary air flowrates were performed by traversing a pneumatic thermometric combination probe downstream of the rotor.
A complete set of numerical simulations was run concurrently with the testing to determine how well they captured the flow physics, particularly the interaction of the ejected secondary streams with the primary flow. The JAXA in-house code, UPACS, and its best practice settings, based on past verification and validation efforts, were employed and not intentionally tuned to better fit the data. The investigation applied both steady and unsteady approaches. Given the study’s primary goal, important features such as coolant holes, internal plenums, and wheelspace cavities that affect the interactions were all directly resolved in the calculation rather than simplified by the boundary conditions and/or source-term modeling.
The rotor exit survey in the experiment suggested that the disk forward hub purge and the blowing from the over-tip casing both intensified the passage vortex in the cascade. In contrast, it was indicated that a positive effect also resulted from ejection from the tip casing, diminishing the tip leakage vortex. The stage performance evaluation implies that the resulting gain may offset or outweigh the negative effects of injection. Additionally, the data suggested that coolant blown off the airfoil has an impact also on the near-endwall zone in particular and can boost (by vane coolant) or weaken (by blade coolant) the secondary flow.
Experimental Investigation of Mode-Frequency Scattering at Fan Stages
Authors: Behn Maximilian , Tapken Ulf 
Published: September 2023

Abstract
For the development of low-noise fan designs the sound generation must be reduced at the source, but also sound transmission effects through the rotor can be exploited to reduce the noise emitted to the far-field. Rotor shielding has been identified as a means of noise abatement, where rotor counter-rotating modes are blocked by the rotor and transmit poorly to the inlet. An effect that is rarely considered in this context is mode-frequency scattering at the rotor, which can circumvent the blockage effect by shifting the sound energy in frequency and mode order, typically to a rotor co-rotating mode order that transmits efficiently to the inlet. An experimental investigation is presented, where the transmission, reflection and scattering of individually generated modes through a fan stage is measured by means of a loudspeaker array and microphone arrays, upstream and downstream. The highly resolved measured data comprise the variation of mode order, frequency, rotor speed and aerodynamic operating conditions. In this study the focus is on mode-frequency scattering, for which results are presented for high and low rotor speed.
Boundary Layer Analysis of a Transonic High-Pressure Turbine Vane Using Ultra-Fast-Response Temperature-Sensitive Paint
Authors: Petersen Anna , Hilfer Michael 
Published: September 2023

Abstract
The focus of this paper is the impact of surface roughness on the boundary layer caused by a 7YSZ thermal barrier coating (TBC). Experimental investigations are conducted on a NGV installed inside the Wind Tunnel for Straight Cascades Göttingen (EGG). The shape of the vane has been altered in a way that eliminates the influence of the TBC’s thickness. Therefore it is expected that only the surface roughness is influencing the location of the separation and boundary layer transition. The transition next to the roughness can also be affected by positive and negative pressure gradients, separation, and interacting shocks.
The impact of TBC on the turbulent wedges’ appearance, separation bubble’s position and length, and transition location is examined in this study. This research, combined with prior investigations, provides comprehensive understanding of a turbine vane’s aerothermodynamics. To investigate unsteady flow phenomena on a TBC coated NGV, ultra-fast-response temperature-sensitive paint (iTSP) is utilized. This dataset will serve as a reference point for developing new turbine vane designs that include TBC and extensive cooling. Furthermore, the findings will be employed as a benchmark for improving numerical models.
A CFD-Assisted Throughflow Approach for the Map Calculation of Centrifugal Compressors
Authors: Labat Casajust Sandra , Möller Daniel , Jeschke Peter 
Published: September 2023

Abstract
In this paper we describe the development of a CFD-assisted throughflow approach for the map calculation of centrifugal compressors with an unshrouded impeller. We focus on the modeling of slip factor, impeller outlet aerodynamic blockage, and entropy loss coefficient as a means of controlling our performance prediction of pressure ratio and efficiency, and study two compressors of similar nominal characteristics. Firstly, we build a baseline calculation with a unified combination of literature models. To address the discrepancies between the baseline solution and CFD results, we define a calibration approach which is based on parameters that can be extracted from a throughflow method and that are representative of secondary flows and flow separation. This approach leads to an improved efficiency prediction for both of our test cases, especially for the lowest and highest rotational speeds. As regards the pressure ratio, an accuracy improvement of 12.9% is achieved for the 100% speed line of one of our compressors. To summarize, we present here a methodology that is able to successfully correct the performance prediction of throughflow calculations for centrifugal compressors. Although the number of machines under consideration in this paper is relatively low to establish general correlations, the approach can be potentially generalized to cover other similar compressors, thus allowing continuous improvement of the models with new data.
On the Effect of Purge Air on the Aerodynamic Performance of a State-of-the-Art Turbine-Rear-Frame Guide Vane
Authors: Schien Malte , Wakelam Christian , Graiff Mattia , Göttlich Emil , Marn Andreas 
Published: September 2023

Abstract
It is well known that the total pressure ratio and the turbine inlet temperature need to be increased to raise the thermal efficiency of a turbine stage. Therefore, a high exit gas temperature of the combustion chamber is essential to increase the thermal efficiency of aero engines. Consequently, the fluid temperature at the inlet of the Turbine Rear Frame (TRF) rises, too. Without any countermeasures, too hot fluid can enter the cavities between stationary and rotating parts through axial gaps causing damage to structural parts. To prevent such ingression of hot fluid, cold purge air is blown out of the cavities and hence interacts with the main flow of the low-pressure turbine.
The present paper investigates the effect of purge air on the aerodynamic performance of a state-of-the-art Turbine Exit Guide-Vane (TEGV) design. For this purpose, five-hole-probe data for three different purge-air flow rates are compared at the inlet and the exit plane of a scaled full annular TEGV cascade. It was found that purge air migrates along the hub end wall toward one TEGV suction side, corresponding to the cross-flow pressure gradient, where it accumulates. The accumulated purge air curls into one vortex. The influence of three TEGV incidence angles, high-negative and high-positive values, is discussed for the nominal purge condition. The investigation was conducted at the Institute of Thermal Turbomachinery and Machine Dynamics of the Graz University of Technology.
Self-Organization of Unsteady Full-Annulus Flows in a Gas Turbine Compressor Under Operating Conditions
Authors: Hagita Yasuharu , Hayakawa Riku , Miyazawa Hironori , Furusawa Takashi , Yamamoto Satoru 
Published: September 2023

Abstract
In Japan, gas turbine combined cycle (GTCC) power plants are currently operated under rapid start-up, shutdown, and partial-load conditions to maintain a stable power supply, suppressing the fluctuation of electric power due to renewable energy sources such as solar and wind power. The off-design condition may cause unsteady and unstable flows in the compressor stage, increasing mechanical stresses on the blades. To reveal the critical flow behavior and avoid blade failure, an innovative method that can clarify the flow physics in these systems is urgently required.
This study proposes a classification method for time-series big data obtained from full-annulus flow computations under various flow conditions assisted by the self-organizing map (SOM) method, which is a popular machine-learning technique. First, full-annulus unsteady flow computations under various flow conditions were conducted for an actual compressor in an industrial gas turbine at a GTCC power plant. The inlet guide vane (IGV) angle was set to various values that corresponded to the full-load operation and transitional flow rate conditions during partial-load operation. The time-series data of the load on the blades in the various cases were obtained from the computations. All time-series data were converted into frequency data using fast Fourier transform (FFT) and classified by the SOM. As a result, the proposed classification method could appropriately classify the critical flow conditions in which large and unstable pressure fluctuations are observed. This method may be used to avoid critical operating conditions that lead to blade failure.
Realtime CFD Based Shape Optimization Using Geometric Deep Learning for Families of Turbomachinery Applications
Authors: Gouttiere Alexandre , Alessi Giacomo , Wunsch Dirk , Zampieri Luca , Hirsch Charles 
Published: September 2023

Abstract
A Machine Learning approach is applied to the open domain test case Rotor 37 to predict the performance of a family of turbomachinery. A deep learning approach implemented in the form of a geometric convolutional neural network is used. A first low geometrical variability parametric representation of the Rotor 37 is created to build training dataset from which the machine learning model is trained. After the training, the model predicts machine performance parameters in a few seconds. Then, this AI model is used in an optimization process to improve Rotor 37 performance and an increase in isentropic efficiency of 2.86% is obtained. A CFD validation is performed to confirm the improvement with an increase of 1.81% in isentropic efficiency. However, the achievable performance increase is limited by the parametric representation generated, given its low degree of freedom. Therefore, a new parametric representation is generated allowing more complex variations of the Rotor 37 design. It is demonstrated that a continuous learning approach, which is used to extend the model can successfully be applied to extend the trained AI model to the larger geometrical variability at significantly reduced model training costs. Then the optimization procedure is repeated and an increase of isentropic efficiency of 3.25% is obtained. A CFD simulation confirms an improvement of the performance of 2.35% in isentropic efficiency.
Rotor Clearance Flow Measurements Employing a Novel Miniature Sensor
Authors: Eck Mario , Peitsch Dieter 
Published: September 2023

Abstract
A miniature flow sensor has been used to investigate the unsteady over-tip flow field in an axial compressor rotor. Flush mounted on the casing wall, the sensor yields the two-dimensional flow field over the rotor blade tip, both in the absolute and relative frames of reference or the wall shear stress distribution on the casing wall. The velocity vector fields phase-averaged to the rotor have been used to compute streakline patterns providing insights into secondary flows including the clearance vortex dynamics, as if the oil flow visualization had been applied in the rotor frame of reference. Using the velocity vector field, the blockage factor has been determined for each individual rotor passage, indicating noticeable variance over the circumference. The variance also increased non-linearly while throttling of the compressor. The vector patterns additionally served to characterize the shear layer between the clearance and the main flow. For this purpose, 2D contours of the divergence and the shear strain rate have been processed first. In a second step, both quantities were reduced to scalar values for each rotor passage by integrating them along the shear layer. This allowed identifying a clear correlation between blockage, divergence and shear strain rate as a function of mass flow. The results contribute significantly to a better understanding of the clearance flow in axial compressors operating at near stall conditions.
Turn-Down Capability of Ansaldo Energia’s AE94.3A
Authors: Piola Stefano , Bavassano Francesco , Benvenuto Marcello , Canepa Roberto , Garbarino Tiziano , Pestelli Elena 
Published: September 2023

Abstract
At an ever-faster pace, market’s requirements for operational flexibility and turn-down capabilities are becoming the fundamental driver for heavy-duty gas turbine design and upgrade. This enables better compensation of the natural intermittence of renewable energy sources such as wind and solar by effectively compensating for both surpluses and shortages compared to the electric grid power request. Gas turbine-based energy plants require a lowest Minimum Environmental Load (MEL) for times when the power request is mainly covered by renewable sources and, however, need to promptly respond to green energy shortages. Ansaldo Energia has been addressing such requirements overall its gas turbine portfolio for several years, recently including further extension of MEL for GT26, as discussed in GT2021-59457.
The present paper addresses the development project carried out to reduce the MEL for AE94.3A via a modular upgrade package especially intended for the wide existing Service fleet, made of more than 110 units. In order to accomplish the AE94.3A MEL reduction, several features were designed and tested including VIGV extra-closure, air bypass through compressor blow-off lines and extended use of anti-ice air recirculation. None of these require major hardware changes but only upgrades within a normal service outage, together with minor control system adaptations. The wide-ranging technical challenges attached to the MEL reduction features are discussed. Validation on field via special instrumentation focused on compressor, secondary air system and turbine for several engines is also presented. The achieved Minimum Environmental Load reduction is shown and its potential discussed together with some features already in place, such as the use of CO catalyzer or the regulation of control valves put on external cooling lines. The readiness and performance level of this MEL upgrade package, already in operation on several power plants, is here demonstrated. This makes the AE94.3A gas turbine more flexible towards current and future market requirements.
Tail-Integrated Boundary Layer Ingesting Propulsion Systems for Turbo-Electric Aircraft
Authors: Chen Zhibo , Galbraith Marshall C. , Spakovszky Zoltán S. , Greitzer Edward M. , Sabnis Jayant S. 
Published: September 2023

Abstract
This paper presents conceptual design guidelines and results for a tail-integrated propulsion system for a turbo-electric civil transport aircraft with boundary layer ingestion (BLI). The aerodynamic performance goal is separation-free and shock-free operation at cruise with fuel burn reduction, compared with a baseline conventional aircraft for the same mission. The assessment of BLI benefits is based on calculations using CFD and TASOPT software, both to characterize the design challenges and to establish the physical mechanisms for resolving these challenges. The guidelines include a “horseshoe” inlet to accept the non-uniform flow without incurring separation, a nacelle profile similar to supercritical airfoils to reduce shock strength, and an annular nozzle to eliminate flow separation between tail-BLI propulsors. The conceptual design has nine BLI propulsors with electric fans on an axisymmetric tail of a single-aisle aircraft. The fans are powered by twin underwing turbofans. The estimated benefit of the tail-BLI, twin underwing turbofan aircraft is 10.4% in Payload-Range Fuel Consumption (PRFC) at a cruise Mach number of 0.8, compared to a baseline twin underwing turbofan configuration. Sensitivity studies further show that a 1% increase in installed (i.e. with BLI) fan isentropic efficiency translates to 0.8% rise in PRFC benefit.