bluuebunny/crossref_metadata_2025_split huggingface dataset:
High-Fidelity Investigation of Vortex Shedding From a Highly-Loaded Turbine Blade
Authors: Gloerfelt Xavier , Cinnella Paola 
Published: August 2024

Abstract
High-fidelity numerical simulations based on wall-resolved large-eddy simulations (LES) are used to investigate the vortex shedding dynamics in a linear turbine cascade. The profile geometry is the well-documented LS59 highly-loaded rotor blade. The simulation campaign covered several outlet Mach numbers (subsonic and transonic) and several experimental configurations to shed light on the relations between vortex shedding frequency, the laminar or turbulent states of boundary layers and the resulting cascade losses. A first major result concerned experiments for transonic outlet Mach number. LES without inlet turbulence and without tripping the suction side boundary layer are unable to match the experimental flow field. In the untripped case, the recirculation bubble is shorter leading to a vortex shedding Strouhal number of 0.17, whereas in simulations with trip wire or inlet turbulence the bubble was longer, with a Strouhal of 0.24. A second finding is that the inlet turbulence intensity is able to drive the switching between two regimes for subsonic outlet Mach numbers: a so-called ‘detached vortex shedding’ (long bubble, St ∼0.24) or a ‘transonic vortex shedding’ (short bubble, St ∼0.19). The appearance of shock waves and very coherent rolls in the wake for the ‘transonic’ regime can lead to a doubling of the cascade losses due to the drastic pressure drop near the trailing edge. Such a change in the flow regime, due solely to an increase in freestream turbulence, has not been reported before.
Aerodynamic Shape Optimization of a Stator
Authors: Dehpanah Payam , Doolittle C. J. , Fuetterer Carsten , Brenner Mattia 
Published: August 2024

Abstract
In this paper, a numerical study conducted on a compressor stator is presented. The results are compared with existing literature and experimental data. For this purpose, a grid refinement study for the baseline geometry at the design condition with an unstructured mesh family is performed. The total pressure loss coefficient and the exit flow angle are compared against the experimental data. Moreover, the corner separation on the suction side is compared against the experimental data. Subsequently, a multi-objective optimization is performed on the baseline geometry to improve two objectives: flow deviation angle and total pressure loss coefficient at the stator exit. For the CAD-based optimization, a parametric model with 55 design variables is built in the parametric design platform CAESES. This parametric model is fitted to the baseline geometry to start the optimization process. The Flow360 compressible flow solver is employed for the steady RANS analysis, utilizing the Spalart-Allmaras turbulence model. The surrogate-assisted multi-objective genetic algorithm (MOGA) is employed for the optimization. Non-uniform profile boundary conditions, obtained from experimental tests, are applied at the inlet. The results for the baseline simulation at the design condition demonstrate strong agreement with both experimental and numerical findings. In the optimal Pareto front solutions, both objectives exhibit improvement. The optimal solution is compared with previously published results in literature.
Reversionary Control Modes for the Mitigation of Failures in a Partially Turboelectric Aircraft Propulsion System
Authors: Simon Donald L. , Chicatelli Amy K. , Bianco Santino J. , Horning Marcus A. , Saus Joseph R. 
Published: August 2024

Abstract
In support of emission and fuel burn reduction goals, the aviation industry is actively pursuing the advancement of electrified aircraft propulsion (EAP) technology. This includes turboelectric and hybrid electric propulsion designs that combine gas turbine engine and electrical system hardware. Such architectures exhibit a high degree of coupling between subsystems. This drives the need for system-level control strategies to ensure the safe, coordinated, and efficient operation of all subsystems. The design and certification of any aircraft propulsion system requires that all potential subsystem failures are identified, and the hazards posed by these failures are appropriately mitigated. This requirement is particularly challenging for EAP systems due to their integrated nature. One approach to assist in EAP failure mitigation is the inclusion of automated reconfiguration capabilities within the propulsion control system. Such control modes, referred to as reversionary control modes, are designed to automatically detect failures and activate backup control modes upon failure detection. This paper covers the design and evaluation of reversionary control mode logic developed for a partially turboelectric propulsion concept. Test results from a real-time hardware-in-the-loop evaluation of the concept are also presented and discussed. The results show that the developed reversionary control logic can successfully detect and mitigate subsystem failures in a representative environment that includes actual electrical system hardware.
Natural Gas Overhung Pipeline Compressor Rotordynamic Design, Test Validation, and Consideration of Morton Effect
Authors: Li Wei , Braman Christopher , Hatori Hiroki , Thorat Manish , Pettinato Brian 
Published: August 2024

Abstract
This study examines a natural gas pipeline compressor design and its potential for “Morton effect” instability. The compressor is designed to utilize a rotor with two tandem stages arranged in an overhung configuration. An overhung rotor design allows for increased compressor efficiency by lowering the inlet losses in the compressor, eliminating a balance piston, and minimizing leakage by having only one dry gas seal. Comprehensive rotordynamic analysis was performed on the rotor-bearing system accompanied by an iterative design optimization. The rotordynamic unbalance response and stability characteristics were good and met the API requirements. Another important aspect “Morton effect” for overhung rotor was also carefully examined because the rotor design has large overhung weight, long overhung length and high bearing surface speed making it subject to a high Morton effect (ME) risk. Bearing optimization, for example, using offset pivot tilting pad bearing and adjusting bearing clearance was performed to minimize the ME risk through the ME analysis. Eventually a test rotor was built to experimentally validate the rotordynamic performance of the worst cases rotor-bearing design, which had minimum clearance at the bearings. The rotor was operated up through its trip speed. Testing was performed to validate that the rotor design is rotordynamically sound and there is no ME within the operating speed range of the rotor.
An attempt was then made to induce ME by altering the bearing configuration from the intended design to one where ME would be more likely. Larger amounts of unbalance were applied. Some additional amplitude and phase change was observed; however, this did not become the classic ME instability.
Understanding EBC Lifetimes and Performance for Industrial Gas Turbines
Authors: Ridley Mackenzie J. , Lance Michael J. , Aguirre Trevor G. , Kane Kenneth A. , Pint Bruce A. 
Published: August 2024

Abstract
Hydrogen or hydrogen blend fuels are expected to replace natural gas in land-based industrial gas turbines (IGTs) to support a greener power economy. Silicon carbide (SiC) base ceramic matrix composites (CMCs) are considered for replacement of Ni-based superalloys to facilitate future efficiency improvements. SiC CMCs require environmental barrier coatings (EBCs) to mitigate volatilization from high-temperature steam, thus making the EBC lifetime critical information for identifying CMC component lifetimes. The goal of this project is to determine the maximum bond coating temperature underneath the EBC for achieving an IGT component lifetime goal of 25,000 h, which is far greater than current CMC component lifetime requirements for aero-turbine applications. To provide data for the lifetime model, laboratory testing used plasma-sprayed rare-earth silicate EBCs on monolithic SiC substrates with an intermediate Si bond coating. Specimens exposed to 1-h thermal cycles in flowing air-steam environments and reaction kinetics were assessed from 700°-1350°C by measuring the thickness of the thermally grown silica scales. The silica growth and phase transformation appear critical in predicting EBC lifetime and several strategies have been explored to reduce the oxide growth rate and improve EBC durability at elevated temperatures. Advanced characterization using Raman spectroscopy has helped clarify this system.
Experimental Investigation on the Effect of Inlet Temperature on Thermoacoustic Oscillation in a Centrally-Staged Combustor
Authors: Ma Jinglong , Han Xiao , Yang Zhipeng , Hui Xin 
Published: August 2024

Abstract
Self-excited thermoacoustic oscillations frequently manifest in lean premixed prevaporized (LPP) centrally-staged combustors, impacting the dynamic characteristics of flames and potentially causing damage to combustor components. Due to the susceptibility of thermoacoustic oscillations to passive control factors, this study explores the influences of the combustor inlet air temperature on these oscillations. The two investigated schemes in this study exhibit thermoacoustic oscillations at 400 K, and as the inlet temperature increases, the overall oscillation amplitude of the system decreases, reaching approximately 50 Pa at 600 K. A noteworthy observation is that at 450 K, the oscillation amplitude of the counter-swirl (CNS) scheme exceeds that observed at 400 K. Furthermore, the shapes and CH* chemiluminescence intensities of the flame are determined through time-averaged and Abel-inverted transform methods, allowing for the characterization of the dynamic features of the flame. By combining insights from the local Rayleigh map, it is found that the driving thermoacoustic oscillation occurs at the inner/out shear layer and the region where the main and pilot flames intersect. A stronger thermoacoustic oscillation in a region indicates a more pronounced coupling between pressure and heat release fluctuations. Hence, exploring the mechanism through which the inlet temperature influences thermoacoustic oscillations is beneficial for the design and optimization of the combustor.
Mechanical Properties of the Support Structure With Recoverable Stiffness
Authors: Sun He , Zhang Dayi , Zhang Qicheng , Yang Cheng 
Published: August 2024

Abstract
The Fan Blade-Off event can have a significant impact on the rotor, and fuse structures are commonly employed to absorb the resulting energy. However, fused structures often lead to excessive loads on other bearings. In this paper, we propose a support structure with recoverable stiffness, integrating a chiral structure using shape memory alloy and a folding squirrel cage. The mechanical properties of chiral unit-cells with various configurations are analyzed. An analytical model of the support structure is established to examine mechanical properties, and the findings are validated through experiments. The support structure can effectively absorb impact energy through the phase transition of materials. The support stiffness rapidly decreases, reaching negative stiffness, and can be restored through heating. Experimental results indicate that the support stiffness aligns with the analytical model, with a stiffness reduction ratio of up to 61.81%. The support stiffness can be fully restored, and the loss factor of the support structure is 0.32. The proposed support structure proves to be effective in absorbing impact energy and achieving stiffness recovery. This, in turn, reduces rotor amplitude and enhances rotor working stability. It stands as a secure and efficient support structure capable of handling impact loads.
Comprehensive Understanding of TGO Morphology Effect on the Thermal Barrier Coatings Failure Under Free Edges
Authors: Qiao Da , Zeng Wu 
Published: August 2024

Abstract
The growth stresses induced by the thermally grown oxide (TGO) will be amplified at the free-edge site, making the free-edge site a weak part of the thermal barrier coatings (TBCs). In this study, the TBCs failure behavior is investigated based on different TGO morphologies under free edges. The thermo-mechanical model is established by creating straight lines and simplified sinusoidal curves, respectively. Dynamic TGO growth is realized by the secondary development of the subroutine. The cohesive element is inserted at the TC/TGO interface to simulate the delamination. The stress evolution near different TGO morphologies under the influence of the free edge are examined. In addition, the interfacial cracking behavior near the free edge is also explored. The results show that the appearance of the free edge will deteriorate the stress condition in the nearby area, change the preferred cracking area, and induce the earlier failure behavior. The straight line morphology has the most “friendly” stress distribution. The sinusoidal curves have peaks and valleys, and different areas of the TGO shape are different under the influence of the free edge, but all of them have the effect of stress “convergence”. These results can provide significant guidance to develop the next-generation advanced TBCs.
Revisiting Dimensionless Parameters Quantifying Film Cooling
Authors: Lee Chien-Shing , Shih Tom I-. P. , Straub Douglas , Weber Justin 
Published: August 2024

Abstract
Effectiveness of film cooling (η) has been characterized by the density (DRh) and blowing (BRh) ratios. In this study, a dimensional analysis and a computational study, based on steady RANS with and without conjugate heat transfer, were performed to identify and examine parameters needed to quantify η, where film cooling is crossflow fed instead of plenum fed. The test problem studied is film cooling of a flat plate, where the cooling air, issuing through 30-degree inclined circular holes, is fed from a cooling channel with a flow direction that is perpendicular to the direction of the hot-gas flow. For this test problem, dimensional analysis shows an additional blowing ratio is needed, denoted as BRc, to quantify η, and BRc is the ratio of the mass flux through the film-cooling hole to the mass flux in the cooling channel upstream of the film-cooling hole. CFD results obtained by varying the mass-flow rate in the cooling channel, while keeping the DRh and BRh constant (DRh = 1.9 and BRh = 0.75 or 1.0), show reducing the mass-flow rate in the cooling channel by one half, which doubles BRc (from 2.6 to 5.2) to slightly affect the discharge coefficient (&lt; 5%) but up to 25% on overall cooling effectiveness and up to 85% on laterally-averaged adiabatic effectiveness. Results are presented that show the flow mechanisms induced by BRc. This computational study was validated by comparing with experimental data generated at the National Energy Technology Laboratory.
A Wide-Bandwidth and High-Resolution Identification Method for the Dynamic Characteristics of Annular Gas Seals Using Hilbert Transform
Authors: Wang Tianhao , Li Zhigang , Li Jun 
Published: August 2024

Abstract
Efficient and accurate parameter identification methods are urgently needed to develop high-performance sealing devices. Although the existing prediction methods have been widely validated, researchers are still grappling with the trade-off between frequency resolution and computational cost. This paper proposed a Hilbert-transform-based time-frequency analysis method to identify the dynamic characteristics of annular gas seals. The frequency-sweep whirling orbit model (FSM) was adopted as the excitation signal of rotor whirling motion. The transient flow field within the seal clearance was numerically simulated by the computational fluid dynamic (CFD) solution combined with the mesh deformation technique. The empirical amplitude-modulated (AM) and frequency-modulated (FM) decomposition and the direct quadrature method were utilized to approximate the analytic signals of the monitored response forces. High-resolution and frequency-dependent dynamic coefficients were determined by the Hilbert transform (HT) of the linear response-force/rotor-motion model. To validate the present method and determine the frequency-sweep mode, the dynamic coefficients of three typical annular gas seals, including a labyrinth seal (LABY), a fully-partitioned pocket damper seal (FPDS), and a hole-pattern seal (HPS), were evaluated by the linear and quadratic frequency-sweep modes, respectively. The results indicate that the dynamic coefficients obtained by the quadratic FSM are all in good agreement with the experimental data, and have almost the same accuracy as the well-known multi-frequency whirling orbit model (MFM). Combined with the proposed adaptive timestep scheme, the present method can obtain the high-frequency-resolution dynamic coefficients of annular gas seals with a 48.6% reduction in the computational time compared to the MFM. Furthermore, the application of the present method in wide-bandwidth cases was also illustrated.
An Aero Engine Disk Sizing and Weight Estimation Approach With Improved Temperature Profiles
Authors: Zaimis Ioannis , Carpentari Elias , Begiebing Tim , Gümmer Volker 
Published: August 2024

Abstract
During the predesign phase of an aero engine, interdisciplinary parametric studies are crucial for identifying an optimum engine. As innovative engine concepts emerge, it is essential to study trends aiming to minimize climate impact and one of its key contributors, fuel burn. The comparatively heavy disks, subjected to high thermal and mechanical loads, are central to this analysis due to their high impact on the overall module mass. This paper proposes an approach to achieve a first lightweight mechanical design of disks in the predesign phase.
Based on a performance and aerodynamic baseline, the design space and physical boundary conditions are set. Firstly, an initial mass optimized disk is derived using simplified temperature profiles and stress calculations under the Mechanical Design Point conditions. Subsequently, all the module disks are considered and an estimation for each bore temperature is achieved through a novel loop over the entire module and all available operating points. By evaluating the temperature and stress profiles across various operating conditions, the low cycle fatigue life of each disk can be studied. As part of a highly modular engine predesign framework, this method allows for zooming capabilities of single disk calculations by prescribing individual boundary conditions. The proposed approach already yields an initial assessment of the rotors within a short runtime, facilitating simple iterations with the succeeding design phases due to method and tool commonalities. While the primary focus of the current work is on compressor design, the principles presented are adaptable and expandable to turbine disk applications as well.
Experimental Investigation and System Simulation Analysis for the Aerodynamic Performance of a Two-Stage Axial Compressor With Inlet Dynamic Distortion
Authors: He Rong , Wang Tong , Liu Yongwen 
Published: August 2024

Abstract
The performance and reliability of a compressor can be adversely affected by its inlet conditions. In this paper, the effect of planar wave on a two-stage axial compressor is investigated experimentally with aperiodic inlet dynamic distortions generated by the insertion and extraction of a plate at the compressor inlet. The transient pressure is measured by the high-response static pressure sensors at different axial and circumferential positions in the flow path. It is found that the inlet distortion is attenuated greatly by the IGV cascade, and then behaves as a planar wave at the inlet of the first stage. At the near-stall operating point, the axial compressor gets through the unstable condition with a hysteresis loop in the performance map by the inlet planar pressure ramp. The hysteresis loop, including asymmetric stall development and recovery processes, is discussed. The sudden pressure increase is found at the beginning of the loop and it could be used as a pre-cursor of stall inception. The inertia of the flow in the loop is discussed with the so-called lag parameter. The inertial effect is more evident in the stall development process than in the recovery process. It is believed that the experimental method with the distortion generation way could be applied widely in the study of the unstable operation characteristics of axial compressors.
The Development of Turbulence Quantities in Different Intermediate Turbine Duct Configurations
Authors: Hafizovic Asim , Krajnc Nicolas , Merli Filippo , Staggl Marian , Mangini Francesco , Sterzinger Patrick Zeno , Marn Andreas , Göttlich Emil 
Published: August 2024

Abstract
The experimental investigation examined the influence of high turbulence intensity, large scales, and turbulence anisotropy on turbulence decay within the intermediate turbine duct (ITD). The paper focuses on two different test configurations of the intermediate turbine duct, which is an annular s-shaped channel used in turbofan engines to guide the flow from the high-pressure turbine (HPT) at a smaller radius to the low-pressure turbine (LPT) at a higher radius. Two state-of-the-art intermediate turbine duct concepts are in focus. The most common duct is the turbine center frame (TCF), featuring non-turning struts. The exit-to-inlet area ratio of the TCF is higher than one, leading to a flow deceleration through the duct.—On the other hand, the turbine vane frame (TVF), also known as integrated concept, can be considered as a direct evolution of the diffusive duct. The integrated concept involves integrating the function of the LP turbine’s first vane row into the duct by introducing turning struts and splitters. However, the turning struts and splitters cause an acceleration in the tangential flow direction while deceleration in the meridional direction occurs. The overall Mach number increases from the inlet to the exit within the component.
The present study obtained hot-wire anemometry measurements using a triaxial and a single hot-film probe. The experiments were conducted in a two-stage, two-spool transonic turbine test rig at the Institute of Thermal Turbomachinery and Machine Dynamics at Graz University of Technology, which includes relevant purge and turbine rotor tip leakage flows. The two test setups include the same (HPT) stage, different intermediate turbine ducts, and a low-pressure vane or blade row, respectively. Several methodologies were used to process the data and to obtain the autocorrelation function, integral length scale, and turbulence kinetic energy dissipation rate.
The turbulence quantities at the inlet to the ducts show the same characteristics in both configurations. The acquired measurement data illustrates different turbulent mixing within the intermediate turbine duct. Moreover, the high turbulence quantities at the exit of the TCF duct dominated the shroud region. In contrast, the flow field at the TVF exit is dominated by TVF secondary flow and vane wakes. These results acquired under engine realistic rig flow conditions enable a deeper understanding of the relationship between loss and turbulence quantities for different intermediate turbine duct configurations.