bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Characteristic-Based 1D Axial Compressor Model for Stall and Surge Simulations
Authors: Kissoon Sajal , Righi Mauro , Pawsey Lucas , Pachidis Vassilios , Tunstall Richard , Roumeliotis Ioannis 
Published: September 2023

Abstract
A low-order unsteady one-dimensional axial compressor and combustor model has been developed at Cranfield University as part of a larger unsteady gas turbine engine model, with the ability to simulate compressor stall and surge. The flow is resolved using the 1D unsteady Euler equations and source terms are used to model bleed extraction (and addition), pressure losses, and heat and work exchange. Species tracking is used in the combustor part of the model, using a semi-coupled approach, to keep track of the combustion products and unburnt fuel in the main gas path. The equations are solved using a Roe Approximate Riemann Solver, modified to handle the high magnitude, transient source terms necessary for this simulation. The performance of the compressor during the transient surge event is described by a set of compressor characteristics, including reverse flow and rotating stall regions, obtained from a validated 3D throughflow code, ACRoSS. To replicate the exact response of multi-stage compressors, stage-by-stage characteristics are used during reverse flow.
The low-order method presented is successfully verified against ACRoSS for a high-power surge event of a coupled IPC and HPC configuration. The rate at which the total pressure at the outlet of the HPC collapses was calculated to be within 1%. This approach presents a faster alternative to high-fidelity CFD and can be used to investigate the compressor stall behaviour within minutes during the early design phase.
Surrogate Models for 3D Finite Element Creep Analysis Acceleration
Authors: Abdallah Jason , Depeweg Stefan , Kuznetsova Maria , Nouri Behnam 
Published: September 2023

Abstract
A gas turbine and especially its blades is at the heart of any gas and oil fired power station and thus it is critical to maximize the length of their design life as a key component for successful utilization. Blades weaknesses could affect the whole process of the energy generation, contractual penalty shall be paid in this case and company reputation can be affected. Therefore, it is important to find out the weakness of blades as quickly as possible. One of the central causes of blades’ weaknesses is creep, that is the permanent deformation of material under the influence of mechanical stresses and temperature. Experience gained from real field issues show that high fidelity creep routines and FEA models must be used since the early stages of component design and by field incident investigations. Using high fidelity models in the FEA creep analysis required for turbine blade design and Lifing (Creep Capability, TMF and HCF), requires a run time of 1–8 days for one analysis with one setting of boundary conditions. To exploit the design space based on boundary condition uncertainties, lot of design iteration are needed. To accelerate the computation time of non-linear calculations (TMF, Creep & HCF), we investigate in this paper the integration of machine learning algorithms in lifing (stress, creep strain & displacement) prediction of an internally cooled turbine blade of a large gas turbine.
Roughness Investigations on In-Service High-Pressure Compressor Blades – Part I: An Automated Process for High-Fidelity Roughness Measurements
Authors: Vasilopoulos Ilias , Rostamian Mirco , Voigt Matthias , Meyer Marcus , Mailach Ronald 
Published: September 2023

Abstract
The two-part publication deals with roughness investigations on in-service high-pressure compressor (HPC) blades, both in terms of measurements and simulations. In this paper (Part I), an automated process for performing detailed surface roughness measurements of the blades has been developed. Specifically, a highly accurate Alicona sensor (20x lens; capable of capturing roughness values down to 0.1 μm) was combined with a pick-and-place robotic arm, and the system was trained to conduct roughness measurements on all the different rotor blades of a 10-stage HPC. First, the Alicona measuring device is validated against a NanoFocus device of similar accuracy. Then, a detailed measurement of the roughness on the suction and pressure side of Rotor 2 is demonstrated, using a 100-point grid. This process is further accelerated by using a reduced number of measuring points. The location of those points has been determined by numerical optimization that aims at minimizing the error between an RBF-based approximation model and the detailed measured roughness distribution. Finally, a summary of the roughness measurements through the entire HPC is given (rotors only; before and after cleaning of the blades at an ultrasonic bath) and the paper ends with a discussion of the results.
Diffuser Stall Inception in a High-Pressure Ratio Centrifugal Compressor With Fishtail Pipe Diffuser
Authors: Ogino Atsushi , Nakayama Ryo , Kitamura Eijiro , Fujisawa Nobumichi , Aoyama Satoshi , Ohta Yutaka 
Published: September 2023

Abstract
This paper presents the stall inception of fishtail pipe diffuser investigated by both unsteady and steady numerical analyses. Fishtail pipe diffuser decelerates the air flow from impeller and induces the flow to the combustor by changing the flow direction from radial to axial. Each unsteady numerical simulation with full annulus model and steady simulation with 1 passage model was performed to investigate the stall inception of the fishtail pipe diffuser attached on the transonic centrifugal compressor stage by commercial code for the design speed, where the flow at the diffuser inlet is supersonic. The numerical simulations were well validated by experimental results. The characteristics of speed-lines and stall points by the numerical simulations matched the surge line of the experimental result. In near stall condition, the separation flow was observed on the suction side wall at the bend section of diffuser. The separation extended upstream by further increase of back pressure of diffuser. When the separation affected the boundary layer on throat wall, diffuser stall occurred. To confirm the effect of the bend, the numerical analysis of the straight shape diffuser was also performed. Straight diffuser was confirmed more stable than the diffuser with bend. From these observations, it was concluded that stall inception was the suction side boundary layer separation promoted by the secondary flow due to the bend.
Creep Degradation of Ferritic/Martensitic and Austenitic Steels in CO2 Environment
Authors: Rozman Kyle A. , Oleksak Richard P. , Doğan Ömer N. 
Published: September 2023

Abstract
Current technology uses steam as the medium to transfer gaseous thermal energy to kinetic energy in turbines. The next generation of power generation will use a higher efficiency medium, supercritical CO2 (sCO2) to facilitate the transfer of energy. Steels have a proven track record of resisting creep and corrosion in steam environments, making them a cost-effective choice for structural components of steam turbines. Alternatively, the creep and corrosion response in sCO2 is more uncertain. This research aggregates and compiles the authors’ research in martensitic/ferritic 9% Cr steel and commercially available alloys 309H and 347H stainless steels. These steels were short-term to medium-term creep tested (&gt; 200 but &lt; 1000 h) in flowing atmospheric pressure CO2 at 650°C for screening of mechanical degradation in CO2 environments. Results are compared to creep tests run in laboratory air. Additionally, the effect of specimen thickness was explored for the austenitic steels. The 9% Cr ferritic steels were degraded in CO2 as evidenced by significant reduction in creep life and ductility (elongation at failure). The austenitic steels showed a more complex pattern of behavior, where some thicknesses exhibited shorter, and others longer, creep life in CO2 relative to air. However, all austenitic steels showed reduced ductility in CO2.
Novel Combustion Instability Diagnosis Method With Upstream Pulsation of Repetitive Laser-Induced Plasmas
Authors: Rubiella Clémence , Byun Hosung , Park Youchan , Do Hyungrok 
Published: September 2023

Abstract
In this experimental study, we are presenting the ability of laser-induced plasmas with successive pulsation to identify combustion instabilities (CI) of a premixed lab-scale combustor. An acoustic disturbance equivalent to a shockwave perturbation is generated in the main air supply line of a swirled injector prior to the fuel addition by focusing nanosecond laser pulses of 1.6 W average power at 10 Hz. The shockwaves are attenuated to be strong pressure waves when reaching the combustor and impact the pressure field for short periods. After plasma breakdowns, the system returns back to its original state after 4 ms once the added acoustic energy has been fully dissipated. Given a set geometry, it is observed that the laser-induced breakdown amplifies the characteristic frequency peaks of the combustor system when actuated in cold flow. Furthermore, when applied to reacting flows, the pulsating acoustic perturbations impact the pressure fluctuation in the combustor, e.g., reducing the amplitude of the primary characteristic frequency peak at certain conditions. The identification of the main instability modes thanks to the plasma shockwave provides proof of the potential use of this novel diagnosis strategy in various and complex combustion systems.
Green CAES With Hydrogen
Authors: Gülen S. Can , Taher Matt 
Published: September 2023

Abstract
Increased deployment of intermittent renewable energy resources such as wind and solar PV requires long duration energy storage (LDES) to maximize their utilization.
In this paper, using rigorous process simulation models, it will be demonstrated that CAES technology, when combined with co-located manufacturing and storage of green hydrogen (H2) manufactured by excess renewable energy resources, provides the most efficient option for LDES. Specifically, it will be shown quantitatively that CAES plus green H2, or “green CAES”, is the most sensible approach to H2 storage when the limited amounts that can be generated via electrolysis (requiring exorbitant amounts of excess energy) are considered.
HERMES: A Novel Test Facility for Investigating Structural Dynamics of Aeroengines
Authors: Xu Y. , Szydlowski M. , Muscutt L. , Rix A. , Patsias S. , Ondra V. , Schwingshackl C. W. 
Published: September 2023

Abstract
One of the main challenges when designing aero engines is their high sensitivity to vibration, which can lead to a loss of performance, increased maintenance requirements and in the worst case a catastrophic failure of the engine. The Holistic Engine Rotor MEasurement System (HERMES) was designed and installed in the Dynamics Lab at Imperial College London under the EPSRC Prosperity Partnership - CORNERSTONE to provide experimental insight into how a fully assembled engine under rotating conditions responds to a well-controlled excitation. It will enable research into the different sources of excitation, the transfer path of the vibration energy across the engine, the identification of the locations where energy is being absorbed, and the best measurement methods to quantify vibration levels, and novel analytic tools for the evaluation of vibration events. The test facility allows exploration of the dynamic responses of a fully assembled but non-operational GNOME helicopter engine under rotating conditions. The engine itself is heavily instrumented to measure vibration on both the rotating and static components and is housed in a low-pressure environment to isolate the mechanical vibration from any aeroelastic effects. The commissioning tests have shown that the HERMES test facility is able to generate high quality vibration measurement data providing a full picture of the dynamic response of such a complex system.
Beneficial Effects of Guide Fins on Corner Separation
Authors: Mondin Gabriel , Riéra William , Duquesne Pierre , Ottavy Xavier 
Published: September 2023

Abstract
Corner separation is a major phenomenon limiting the operability of aeronautical compressors. Passive control devices such as guide fins are envisioned to reduce its deleterious effects. In this paper, guide fins are optimized to reduce the total pressure losses downstream of a subsonic compressor cascade (M = 0.11, Re = 3.2 105, modern stator blades) at design and near-stall incidences. Guide fins shapes are defined using 15 parameters. An optimization strategy relying on the iterative refinement of surrogate model with Reynolds-Averaged Navier-Stokes (RANS) computations is carried out. A database of 1033 guide fins is obtained, a large number of which strongly reduces the near-stall losses. Three guide fins are thoroughly investigated and referred to as Short Fence (short and straight guide fin), Long Fence (long and straight guide fin) and 3D (long guide fin with a strong pyramidal aspect). Their effect on the downstream measurement plane is validated experimentally, as well as their integrated performances. Large reductions of total pressure losses at near-stall incidence are obtained (−2.4 pt to −2.9 pt, or a relative reduction of −50% to −60%) without degrading neither the nominal losses nor the stator deflection. These guide fins are used to highlight three beneficial mechanisms that alter the corner separation development within the blade passage a) Tip Vortex (energizes the passage flow) b) Fence (induces 2 passage vortices) c) Guide (induces a local favourable pressure gradient). The role of these mechanisms in the generation of total pressure losses are analyzed in depth with streamlines visualisations and with a topological analysis. Kriging surrogate models reveal that three parameters drive the guide fins performances : the axial position, height, and thickness value at hub. The performances of the investigated guide fins are robust to significant variations of these parameters, as well as small variation of the inlet boundary layer thickness.
A Method of Pseudo-Steady State CFD Calculation to Predict Turbomachine Characteristics
Authors: Goldenberg Vlad , Conser Benjamin , Vorobyova Anna 
Published: September 2023

Abstract
A method for performance-characteristic creation of a turbomachine has been developed to enable smooth characterization across various operating points without the need to simulate these points individually. The method itself involves the initial steady state CFD simulation of a turbomachinery flow path as is standard practice in the industry. This typically involves single blade row RANS analysis. The method involves adjusting the boundary condition(s) to sweep across a characteristic during simulation execution. The change in boundary conditions occurs at every iteration, however the change at each iteration is deliberately made sufficiently small so as not to significantly impact convergence characteristics such as equation residuals. Therefore, even though steady-state is never truly achieved during mapping of the characteristic, the rate of change is small enough that the method can be called a pseudo-steady state result.
In addition to generating a continuous characteristic, the method also enables the extraction and amplification of effects that are not otherwise easily predicted from steady-state CFD methods, and whose prediction and analysis using other methods, such as transient CFD computation, may be significantly more computationally costly. A specific example is the detection of stall/surge phenomena. A mathematical method has also been developed to evaluate stall behavior by applying a gaussian window filter on the convergence history and amplification of the resulting filtered convergence data. The method is most similar to experimental-based methods of stall and surge detection in that they rely on the detection of symptomatic phenomena such as vibration or acoustics rather than evaluation of underlying physics. Here, the detection of relatively small aggregate changes in steady-state simulation behavior is indicative of instability. The method is applied to three sample cases encompassing a broad sampling of turbomachinery: A multistage radial blower, a two-stage NASA transonic compressors, and an inducer pump.
A Multi-Level Design Workflow for Radial Turbocompressors to Create the Database for an Enhanced Cordier Diagram: Development and Proof-of-Concept
Authors: Lattner Yannick , Geller Marius 
Published: September 2023

Abstract
We present the concept of an enhanced Cordier diagram as a digital tool. The enhanced Cordier diagram is designed to replace the original Cordier diagram by significantly extending its functions. The parameters, which must be considered by the enhanced Cordier diagram, are identified. To include all required parameters, a multi-level design workflow for radial turbocompressors is created. It employs computer simulations to analyze the structural load and speed line for various compressor designs and respective geometry variations. Using the multi-level design workflow, 50 geometry variants are created for each of 50 compressor designs. Thus, a database containing the properties of 2,500 compressor variants is obtained. Sensitivity studies are performed to assess the database’s suitability to be used in the enhanced Cordier diagram. The selected input parameters are found able to describe the desired compressor properties. Surrogate models are successfully trained, validating the presented concept of the enhanced Cordier diagram.
Identification of Compressor Vibration Aerodynamic Forcing Mechanisms by Spectral Characteristics
Authors: Hernley Valerie , Kang Jeongseek , Montgomery Matthew , Chung Jae Hoon , Jemcov Aleksandar , Morris Scott C. 
Published: September 2023

Abstract
Non-synchronous vibration (NSV) in axial compressors can be caused either by 1) unsteady aerodynamic forces that are not related to motion of the blades or 2) motion-dependent aerodynamic forcing (e.g., flutter). Aerodynamic forcing mechanisms can be challenging to identify in experimental observations of NSV because the temporal vibration characteristics for both forcing mechanisms can appear similar. This work proposes a method for distinguishing between the two mechanisms using spectral characteristics. The method provides an interpretation of experimental data explicitly consistent with the analytical models used to differentiate between forced response and flutter. Two cases of NSV were observed in a 1.5-stage axial compressor at near-stall conditions. The circumferential wavenumber-dependent unsteady pressure spectra and non-intrusive stress measurement system (NSMS) spectra were observed to have distinct characteristics for the two NSV cases. Based on these distinct spectral characteristics, the first case was identified as blade-row aerodynamic forcing, while the second was identified as motion-dependent (flutter). Numerical simulations confirmed low aerodynamic damping at the conditions where flutter was observed.
Reduced Order Model of Nonlinear Structures for Turbomachinery Aeroelasticity
Authors: Flament Theo , Deü Jean-François , Placzek Antoine , Balmaseda Mikel , Tran Duc-Minh 
Published: September 2023

Abstract
This work concerns the numerical modeling of geometric nonlinear vibrations of slender structures in rotation using an original reduced order model based on the use of dual modes along with the implicit condensation method. This approach is an improvement of the classical ICE method in the sense that the membrane stretching effect is taken into account in the dynamic resolution. The dynamics equations are firstly presented and the construction of the reduced order model (ROM) is then proposed. The second part of the paper deals with numerical applications using the finite element method, first for a 3D cantilever beam, then for an Ultra High Bypass Ratio (UHBR) fan blade. In the applications considered, the proposed method predicts more accurately the geometrically nonlinear behavior than the ICE method.
Numerical Characterization of Prestall Disturbances in a Compressor Stage
Authors: Bicalho Civinelli de Almeida Victor , Tüzüner Ergin , Eck Mario , Peitsch Dieter 
Published: September 2023

Abstract
Compared to the subject of rotating stall, less attention has been given to prestall flow disturbances in turbomachinery. This is mostly due to the fact that these phenomena, often referred to as Rotating Instabilities, do not necessarily or distinctly occur in every compressor and usually last for a long period without posing serious threats to stable operation. The present study aims at numerically characterizing prestall disturbances in detail in a compressor stage in which they have been experimentally observed. Full-annulus CFD computations employing a hybrid scale-resolving turbulence model are performed and compared against unsteady experimental data. Assessment of specific prestall disturbance metrics, including power spectral density, coherence and circumferential mode distribution at the rotor clearance, show that the numerical model is successful in reproducing the unsteady phenomena close to stall inception. Moreover, dynamic mode decomposition is employed to directly link each peak of the unique prestall disturbance spectral signature to spatial structures with different circumferential order. This procedure is done for both 1D circumferential modes, based on flush-mounted pressure probes, and for 2D surfaces exposing the tip clearance dynamics. The high-resolution numerical model, supplemented with vortex identification criteria and data-driven decompositions, enhances the understanding of prestall disturbances and their associated coherent flow structures.
Impacts of Alternative Aviation Fuels on Engine Cycle Design and Aircraft Mission Capability
Authors: Sasi Sarath , Mourouzidis Christos , Roumeliotis Ioannis , Nikolaidis Theoklis , Pachidis Vassilios , Norman Justin 
Published: September 2023

Abstract
Recent 2050 net zero targets for aviation have sparked interest among the industry players to seek alternative aviation fuels as a pathway for the immediate alleviation of its carbon footprint. This paper aims to shed light on the opportunities and challenges that zero & low-carbon alternative fuels can provide from a technical standpoint. To address this aim, candidate fuels for aviation were selected from five broad classes of fuels. Then, a preliminary thermodynamic engine cycle design space exploration of a modern three spool turbofan is conducted to identify the fuel impact on cycle performance. Following that, an integrated Engine-Aircraft mission assessment for a Boeing 787 style aircraft with a three spool turbofan is conducted to assess performance at the mission level and explore opportunities and challenges for both powerplant and aircraft, accounting for fuel storage. Finally, an investigation of the opportunities available for the proposed fuels to be used as a heat sink is presented. The results indicate that zero-carbon fuels expand the design space for the powerplant cycle, allow for higher BPR, lower energy specific fuel consumption, lower peak cycle temperatures compared to the rest of the fuels, and provide significant cycle redesign opportunities. On a mission level, cryogenic fuels are penalized for block energy consumption due to the significant weight and size of the fuel storage system, while liquid alternative fuels are comparable to kerosene in terms of emissions and block energy consumption. Concerning Hydrogen, Methane, and Ammonia, the thermal power requirement for fuel conditioning (pressure and temperature rise) is calculated to be 2.2MW, 1.3MW, and 1MW respectively for a 240kN SLS thrust class engine during take-off.