bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanoindentation study of human fingernail for determining its structural elasticity
Authors: Tohmyoh Hironori , Abukawa Masaru
Published: September 2023

Background

Human nails play an important role in transmitting force to the fingertips, and their mechanical properties are important indices. The nail has a three‐layered structure consisting of top dorsal, middle intermediate, and under ventral plates, and its internal structure is believed to affect its mechanical properties. However, this has not been investigated in previous studies.

Methods

The Young's moduli of the top, middle, and under plates were measured using nanoindentation, and a theoretical model was developed to estimate the structural elasticity for the bending deformation of human nails, which is an index describing the deformability of the nail without depending on its external dimensions. The structural elasticity of human nails was compared with that of human hair collected from the same person. The effect of the softening treatment on the nails was also evaluated.

Results

The Young's moduli of the top, middle, and under plates measured using nanoindentation were 2.9, 3.1, and 2.8 GPa, respectively. The structural elasticity of the nail was estimated to be 2.9 GPa, approximately 75% that of hair. Moreover, softening treatment with a urea cream reduced the structural elasticity of the nail to 70%.

Conclusion

This paper proposed a method for estimating the structural elasticity of a human nail with a three‐layered structure. This index is a mechanical property with “Pa” as a unit, and is useful for comparing deformability with the Young's modulus of other homogeneous materials or for investigating the effect of various treatments quantitatively.
Physically Based Rendering of Animated Point Clouds for EXtended Reality
Authors: Rossoni Marco , Pozzi Matteo , Colombo Giorgio , Gribaudo Marco , Piazzolla Pietro
Published: September 2023

Point cloud 3D models are gaining increasing popularity due to the proliferation of scanning systems in various fields, including autonomous vehicles and robotics. When employed for rendering purposes, point clouds are typically depicted with their original colors acquired during the acquisition, often without taking into account the lighting conditions of the scene in which the model is situated. This can result in a lack of realism in numerous contexts, especially when dealing with animated point clouds used in eXtended reality applications, where it is desirable for the model to respond to incoming light and seamlessly blend with the surrounding environment. This paper proposes the application of physically based rendering (PBR), a rendering technique widely used in real-time computer graphics applications, to animated point cloud models for reproducing specular reflections, and achieving a photo-realistic and physically accurate look under any lighting condition. To achieve this, we first explore the extension of commonly used animated point cloud formats to incorporate normal vectors and PBR parameters, like roughness and metalness. Additionally, the encoding of the animated environment maps necessary for the PBR technique is investigated. Then, an animated point cloud model is rendered with a shader implementing the proposed PBR method. Finally, we compare the outcomes of this PBR pipeline with traditional renderings of the same point cloud produced using commonly used shaders, taking into account different lighting conditions and environments. Through these comparisons, we demonstrate how the proposed PBR method enhances the visual integration of the point cloud with its surroundings. Furthermore, it will be shown that using this rendering technique, it is possible to render different materials, by exploiting the features of PBR and the encoding of the surrounding environment.
Stochastic Multi-Objective Optimization of a Residential Microturbine-Driven CHP System Considering Probabilistic Reliability Constraint
Authors: Teymoori H. Fatemeh , Safari Amir , Kamalinasab Mostafa
Published: September 2023

Recently, micro combined heat and power (M-CHP) systems have been increasingly used worldwide. M-CHP is supposed to play a meaningful role in reducing carbon dioxide emission, increasing energy resource efficiency, and economic saving in the future. This article suggests a new multi-objective optimization approach for optimal planning of microturbine-based CHP systems by considering the uncertainty of equipment availability. The proposed model consists of three competing objective functions: full investment/operation cost, exergy efficiency, and gaseous emissions. To model the uncertainty source, a scenario-based method, using the forced outages of the electrical grid components, auxiliary boiler, and M-CHP, is incorporated into the proposed model. Furthermore, a new achievement function-based directed search domain (AF-DSD) method is proposed to effectively extract the Pareto frontier of this multi-objective problem. The proposed model and solution method are tested on a real-world M-CHP system. The results have shown that, using the AF-DSD method, both sides of the utopia hyper-plane are covered, and all Pareto-optimal solutions can be found for both convex and non-convex problems. The numerical results show that minimizing total cost, primary exergy, and emission promotes an efficient energy supply system where all energy resources are utilized effectively.
Parametric Cycle Studies of the Water-Enhanced Turbofan Concept
Authors: Ziegler Paul , Kaiser Sascha , Gümmer Volker
Published: September 2023

The Water-Enhanced Turbofan is a promising revolutionary concept which addresses the most climate-relevant emissions of aviation: carbon dioxide, nitrogen oxides as well as water vapor and particulate matter which form contrail cirrus. The concept combines the traditional Joule/Brayton cycle with a Clausius-Rankine steam cycle to a dual-fluid cycle also known as the Cheng cycle. While previous publications cover the basic thermodynamics of the concept and give an overview of the potential climate impact reduction, this paper aims to give an overview of important design parameters and their impact on the cycle. In addition, the fuel burn on aircraft system level is assessed with exchange factors for thrust specific fuel consumption and propulsion system weight.

A cooling air model for conceptual design which covers the main effects of steam injection on the required cooling air mass flow is employed. For the heat exchangers a substitute model is used. The substitute model is based on a one-dimensional, discretized tool, using a predefined sizing rule and a linearization for changing inlet condition.

After the main design parameters are identified, parameter studies are performed using a multi-design-point approach. It is shown, that the vaporization process is a major design driver. Furthermore, the water injection mass flow rate is an important parameter both for design and for the operation of the engine as an additional degree of freedom.
Fluid Dynamic Loss Model With Wide Applicability for Aeroengine Transmission Gears
Authors: Arisawa Hidenori , Tanaka Mitsuaki , Hashimoto Hironori , Goi Tatsuhiko , Banno Takahiko , Akahori Hirofumi
Published: September 2023

In high-speed gear systems for aeroengines, it is important to reduce the fluid dynamic loss, which accounts for the majority of power loss, to improve the fuel efficiency. For reasonable loss-reduction and the standardization of low-power-loss designs, a fluid dynamic loss model with wide applicability is needed. However, there are few reports of loss models considering the gear shroud effect on the oil dynamic loss.

This study developed a loss model based on fluid dynamic loss phenomena. Specifically, fluid dynamic loss models were developed for the “air side-flow loss,” “air pumping loss,” “oil-jet acceleration loss,” and “oil re-acceleration loss” in the gear meshing part, and “air vortex loss” and “oil churning loss” in the gear peripheral part, with consideration to the shrouding effect. Moreover, an experimental method and a numerical method for loss classification are proposed.

The fluid dynamic loss models were validated by experiments or experimentally validated numerical simulations. To demonstrate the effectiveness of the loss model for low-power-loss design, the influence of the design parameters was investigated, and the typical parameters were optimized.
An Estimation of Wetness Losses for Nuclear Steam Turbines Using Simplified 1D-2D Models
Authors: Stanciu Mugurel
Published: September 2023

This paper presents a methodology to estimate wetness losses for steam turbines using simplified models. Several 1D solvers are used to evaluate the steam flow field and the droplet nucleation and growth. The results are used as input data for another 2D solver to calculate droplet trajectories, liquid films on blades and wetness losses. These losses are decomposed in several types and modeled according to the classical approaches of Gyarmathy and Laali: thermodynamic, collected water, centrifuged water, drag of fine and coarse droplets, impact, additional friction and exit kinetic energy losses. All HP and LP nuclear steam turbines currently in operation in the EDF’s nuclear fleet are analyzed using this methodology. Several sensitivity studies are also performed to assess the importance of the various physical laws governing the condensation models, the input data used for wetness losses estimation and the values of the parameters involved in the wetness models. The results show that the wetness losses decomposition is strongly dependent on the type of turbine and that the equivalent Baumann coefficients vary depending on the average wetness mass fraction in each stage. The most important factors influencing the wetness losses evaluation are the droplet size and the deposition rate, all other variations of parameters and models playing a less significant role.
Improved Strain-Energy Based Mistuning Models Part I: Motivation, Approach, and Understanding
Authors: Hegde Shreyas , Madden Andrew , Kielb Robert
Published: September 2023

One of the grand challenges in turbomachinery forced response is accurately predicting individual blade responses in a system. This paper helps address these challenges and describes an improved FMM model for computing the mistuned forced response of an embedded compressor rotor. Specifically, the paper concentrates on coupling aerodynamic and structural dynamics into the mistuning model and incorporating a strain energy parameter that can help improve the accuracy of the mistuned prediction, especially in the “veering” region. Previously, the authors published results highlighting a wide range of mistuned predictions and the impact of multi-row interaction on these responses. One gap in the literature is the absence of a robust strain energy-based model, which can help improve the accuracy, particularly for cases in which the system mode family is not isolated, i.e., the mode family lies in the veering region, which in turn leads to a significant amount of strain energy in the disk. The current paper starts from an existing mistuning formulation under the FMM framework and describes two approaches to incorporating the strain energy parameter. The key conclusions are: 1) the non-dimensional mistuning parameters significantly improve prediction by including this strain energy-based parameter. 2) the improved strain energy formulations lead to a significant improvement in the mistuning amplification factor for a non-isolated mode family and help couple the physics better in addition to better predictions for a non-isolated family of modes, 3) The coefficient based mistuning model shows promising results with the calibrated coefficient value being the same at multiple resonant crossings for this configuration.
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

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

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

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

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

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 (> 200 but < 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

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

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

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

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

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

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

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

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

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

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.
Numerical Investigations of Flows and Heat Transfer in Turbine Disc Cavities
Authors: Beaux Jean-Hugues , Girardeau Julian , Khelladi Sofiane , Deligant Michael , Perilhon Christelle
Published: September 2023

In gas turbines, the stator wells play a key role in the efficiency of the turbomachine. The research for performance gains requires a good understanding and an accurate modelling of the flows and heat transfers occurring in these areas. Indeed, engineers try to maintain sustainable temperatures of the turbine components while minimizing the amount of cooling required to do so. Within the framework of the European program MAGPI WP1, a two-stage axial turbine test rig provided an experimental database used to validate the CFD models.

The aim of the current study is to set up a numerical methodology using the CFD solver ANSYS Fluent to accurately predict the conjugate heat transfer in the stator well area. The validation of the methodology relies on thorough comparison of the results with the MAGPI WP1 experimental temperature / pressure measurements. A geometry with axial cooling injection through lock plate slot was chosen. A RANS 3D sectorized CFD model of the turbine with conjugate heat transfer was used. It includes main gas path, cavities with labyrinths, discs rotor, the casing and the Nozzle Guide Vanes (NGV). Mixing planes are placed between the static and rotating frames. Different influences (mesh, turbulence model, thermal boundary conditions, radial labyrinths clearances) were studied and compared with experimental data.

As a baseline, the first calculations were performed with a cooling flow rate chosen so that hot gas ingresses from the main stream into the stator well cavity. Good agreements between predicted and measured temperatures / pressures were observed, especially in the vicinity of the stator well. Discrepancies were spotted at the first rotor hub endwall and at the upstream wheelspace and will be discussed. Finally, a configuration with a different cooling flow rate was conducted where cooling air egresses from the disc rim cavity to the main gas path.
Numerical Investigation of a Thermally Perfect Gas Model for a Centrifugal Compressor Design With Water Vapor as Working Medium
Authors: Kajasa Bojan , Nicke Eberhard , Kügeler Edmund
Published: September 2023

Due to the use of fossil energy sources in the industry sector for which process heat is needed, the footprint on the global climate has increased significantly. The Implementation of High-Temperature Heat-Pumps (HTHP) into industry processes can make a significant contribution to reducing the consumption of fossil energy and thus to reduce the CO2 emissions. In order to realize a high Coefficient of Performance (COP) using natural refrigerants/working medium the application of Rankine thermodynamic cycle is favored. The operation of turbomachinery with a reasonable efficiency within HTHP provides high COPs and the design of the centrifugal compressor geometry considering superheated water vapor as working medium is required. Since a calorically perfect gas model is predominantly used in Computational Fluid Dynamics (CFD) for example for air as working medium with a heat capacity independent from pressure and temperature. Deviations in the evaluated performance can occur when this model is used for designing the centrifugal compressor geometry with superheated water vapor, where the heat capacity coefficients (Cv and Cp) are highly dependent on the temperature. For the numerical investigation of superheated water vapor within the CFD the influence of a thermally perfect gas model is compared to a calorically perfect ideal gas model. The influence on the operating range with respect to the design point is studied and the compressor map trend is investigated. The results of the thermally perfect gas model in the design process on the performance parameters like pressure ratio and efficiency are discussed.
Development of Near-Wall Treatment to Improve Flame Flashback Prediction for Hydrogen Flames
Authors: Choi Minjun , Gu Inyeong , Shin Youngjun , Cho Eun-Seong , Hwang Jeongjae , Kim Min Kuk , Shin Dong-Hyuk
Published: September 2023

Numerical investigations on prediction of flashback of a lean premixed hydrogen flame in an industrial gas turbine combustor were conducted. Three combustion models were tested for prediction capabilities: (i) the flamelet-generated manifold-finite rate (FGM-FR) model, (ii) the flamelet-generated manifold-turbulent flame speed (FGM-ST) model, and (iii) the eddy dissipation concept (EDC) model. Without an additional wall damping model, the three models are unable to predict the flame flashback limit correctly. A wall damping model was applied to modify the reaction rate near the wall. With certain values of the wall damping coefficient, the FGM-FR and FGM-ST models successfully predict the flame flashback limit.
Robust Tip Gap Measurements: A Universal In-Situ Dynamic Calibration & Demonstration in a Two-Stage High-Speed Turbine
Authors: Castillo Sauca Antonio , Paniagua Perez Guillermo
Published: September 2023

Tip clearance monitoring is essential for the active health monitoring of turbomachinery and their development towards more efficient systems. Proper sensor calibration is paramount to this purpose, frequently being a time-consuming process. This paper introduces a novel in-situ dynamic calibration routine for high-frequency capacitance sensor measurements for tip clearance. The method predicts the calibration curve based on a single clearance measurement, the evolution of the acquired signal through various operational conditions, and the dimensional features of the multi-rim squealer-tip passing blades. The experimental data was obtained at 2MHz in a state-of-the-art two-stage high-speed turbine operated by the Purdue Experimental Turbine Aerothermal Lab. A description of the empirical setup is provided, emphasizing the capacitance probes, the conditioning and acquisition systems, the metrology instruments used, and other ancillary instrumentation relevant to the calibration procedure. The prior filtering and data identification from the raw signal is detailed. The step-by-step development of the algorithm is presented, including justification of the curves imposed by the method. The resulting calibrations are provided, achieving accuracies of a few microns. The results are compared against previously used calibration techniques, emphasizing the potential advantages of the presented routine. Finally, the time-resolved tip clearance is analyzed against high-frequency aerothermal data within the gap region, identifying relationships between the tip gap, unsteady pressure, and heat flux on the shroud.
Numerical Analysis of Reversible Radial-Flow Turbomachinery for Energy Storage Applications
Authors: Parisi Simone , Haglind Fredrik
Published: September 2023

Decarbonization of energy systems is expected to require significant amounts of energy storage. Among the different technologies studied, thermo-mechanical storage is being considered for long duration storage due to its low cost and limited usage of critical materials. Based on the experience of pumped hydro plants, significant cost savings can be achieved if a single stage reversible compressor-turbine is used for both the charging and discharging of the storage. Due to the modest (< 4.5) pressure ratio involved, low temperature adiabatic compressed air energy storage and pumped thermal energy storage are considered as candidate applications for reversible turbomachinery.

This paper presents a numerical analysis of an existing high efficiency centrifugal compressor operating both as a compressor and a turbine using mean-line analysis and steady-state simulations with Reynolds-Averaged Navier-Stokes equations in ANSYS CFX. After validation against experimental data in compressor operating mode, the turbine mode was tested by changing only the inlet and outlet boundary conditions and reversing the direction of rotation. Subsequently, a new stage was designed using conventional procedures developed for compressors and evaluated using computational fluid dynamics simulations.

The results indicate that for an up-scaled version of the existing compressor it is possible to reach total-to-total polytropic efficiencies exceeding 86.7% as a compressor and 92.1% as a turbine, which is comparable with the efficiencies of dedicated machines. The new design reaches a polytropic efficiency of 89.4% as compressor and 90.4% as turbine. In both cases the numbers obtained do not include a volute or diffuser cone. Furthermore, the results indicate that there is a compromise between the optimal design for the compressor and turbine mode.
Real-Time Parameter Inference of Nonlinear Bluff-Body-Stabilized Flame Models Using Bayesian Neural Network Ensembles
Authors: Croci Maximilian L. , Sengupta Ushnish , Ekici Ekrem , Juniper Matthew P.
Published: September 2023

We assimilate the parameters of a low order physics-based model of a bluff-body-stabilized premixed flame by observing OH PLIF and PIV images of a 1.1 MW flame. The model is a five parameter level set (G-equation) solver with a prescribed velocity field. A Bayesian ensemble of neural networks (BayNNE) is trained on numerical simulations of the model at 2400 different parameter combinations. Once trained, the BayNNE observes the experimental data and outputs the expected values and uncertainties of the parameters of the model that best fits the experimental data. Using this model, we extrapolate the heat release rate field in physical space beyond the observed window in the experiments, and in parameter space to smaller perturbation amplitudes. We then convert the periodic heat release rate field into a distributed n-τ model, which we enter into a thermoacoustic Helmholtz solver. We find that the thermoacoustic eigenvalue drift is small but measurable, is stabilizing, and does not vary significantly during the experimental run or with the velocity amplitude. This is primarily because the time delay field τ, which is determined by the convection speed, is similar for all cases. This is consistent with the experimental images, which exhibit intermittent bouts of thermoacoustic oscillations that die away. Although this paper’s conclusions for thermoacoustic behaviour are unsurprising, the method it describes is a potentially cheap way to combine sparse experimental measurements with copious low order simulations.
Convergence of Dynamic Mode Decomposition As an Assessment Criteria for Completion of Internal, Unsteady Flow Simulations
Authors: George Amelia , Defoe Jeff
Published: September 2023

The length of simulation time for unsteady computational fluid dynamics (CFD) is often based on intuition or best practices, as there is no established convergence criteria to guarantee the computations have generated enough flow to resolve all spatio-temporal content. Thus, these simulations are often run longer than necessary, but this increases the run time and computational resources required. This is often the case for unsteady CFD for turbomachines. This paper introduces an algorithm, based on dynamic mode decomposition (DMD), that can determine when continuing an unsteady CFD computation no longer yields additional spatio-temporal information. The algorithm is shown to correctly determine the modal content for an analytical dataset with a start-up transient with 44% less data than by only using data from after the start-up transient. The algorithm is then applied to 2D CFD of a fully turbulent flow over a cylinder with periodic boundaries, where the amount of flow time required is just sufficient for the size of fluctuations in cylinder lift coefficient to stop growing. The algorithm is also applied to a 2D periodic flow over a rotor airfoil, with an empty stationary duct downstream. The algorithm determines the point at which the statio-temporal content of the flow stops changing meaningfully greatly in advance of using conventional methods.