bluuebunny/crossref_metadata_2025_split huggingface dataset:
Aerodynamic Design, Study, and Performance Mapping of a Radial-Axial Machine for Geothermal Power Plants in Energy Transition Applications
Authors: Lottini Fabrizio , Marconcini Michele , Arnone Andrea , Biliotti Davide , Foschini Alice 
Published: September 2023

Abstract
Energy transition has become one of the most discussed topics of the current times. Turbomachinery still plays a key role in the power generation field, but the machines must meet very high standards in terms of performance levels, compactness, and cost reduction. In this perspective, new design configurations need to be explored. This paper presents a procedure for the aerodynamic design of a radial-axial stage turbine for geothermal applications. Based on a real set of possible power plant conditions, a dedicated CFD campaign has been carried out to assess the performance of the radial-axial machine — at design and off-design conditions. The main goal of the presented work is to exploit the benefit of combining radial and axial stage architectures, providing a compact, flexible, and efficient machine, capable to maintain high performance levels even at off-design conditions, which is a crucial requirement for renewable energy applications. Since organic fluids with high molecular weight are used in these applications, in addition to the common design procedure based on RANS CFD analyses, real-gas calculations are mandatory to correctly predict the behavior of the machine. All the CFD analyses are performed using the TRAF code, while the design of the radial-axial stages is carried out based both on in-house and commercial tools as per Baker Hughes best practice. The paper highlights the feasibility of the unusual radial-axial architecture as an effective way to combine the benefits of both the radial and the axial configurations, resulting in an efficient, robust, and compact machine.
A CFD-Based Throughflow Solver Using Cascade Potential Theory for Axial Compressor Flow Modeling
Authors: Kravtsoff Florent , Schvallinger Michaël , Ottavy Xavier 
Published: September 2023

Abstract
This paper describes the use of the Hess & Smith cascade potential method as an additional feature for throughflow modeling. This method is incorporated inside ASTEC, a CFD-based throughflow solver developed by Safran Tech providing local blade loading information for blade force and loss modeling. The test cases are all subsonic, composed of two compressors cascades and a low speed compressor. The two profile families for the cascades are a classical NACA 65 009 and a controlled diffusion cascade designed by the Whittle Laboratory. The compressor is the well studied CME2, a research single stage designed by Safran Aircraft Engines. From the potential calculation, boundary layers and wakes are calculated on the blades providing deviation angles and profile losses. The tip leakage losses are also estimated from blade loading at the tip of a rotor. The results are compared to MISES code predictions, RANS simulations, experimental data and classic Lieblein empirical correlations. This work aims to model compressors flow with geometry-based classic analytical methodologies for a minimal use of empiricism. The predictions are good on bi-dimensional cascades cases compared to several other methodologies and at mid-span for the multiple incidences considered compared to experimental cascade results. For the compressor case, the blade loading near mid-span of the rotor blades show good agreement compared to RANS results leading to an overall good capture of the performance characteristic trends near design point. There is still room for improvements near the end-walls, mostly due to the lack of hub boundary layer model in the actual methodology. These results still build a step on which the enrichment of the flow model can be pursued.
Structure and NOx Emissions of Stratified Hydrogen-Air Flames Stabilized on a Coaxial Injector
Authors: Leroy Maxime , Mirat Clément , Renaud Antoine , Puggelli Stefano , Zurbach Stephan , Vicquelin Ronan 
Published: September 2023

Abstract
In recent years, the need for low-carbon power has seen hydrogen emerge as a potential fuel to replace conventional hydrocarbons in combustion to limit CO2 emissions in several sectors, including aeronautics. The challenges posed by hydrogen combustion are similar to the issues of kerosene flames but more challenging, like nitrogen oxide (NOx) emissions and flame flashback. One potential solution to address these problems is to burn a rich mixture of hydrogen and air in globally lean conditions on a coaxial injector to obtain a stable and staged combustion and attempt to reduce emissions. In this article, the evolution of NOx production as more air is mixed into the fuel is studied, as well as the changes in flame size and structure. In particular, the appearance of a secondary flame front is observed and increasing the proportion of air in the fuel mixture both shortens the flame and reduces the NOx emission index. Additionally, the effect of the global equivalence ratio and flame thermal power are studied. Finally, existing models for NOx emission of hydrogen flames on a coaxial injector based on average flame residence time and strain rate are tested and shown to have promising results.
Conjugate Modelling of a Closed Co-Rotating Compressor Cavity
Authors: Parry James , Tang Hui , Scobie James A. , Lock Gary D. , Carnevale Mauro 
Published: September 2023

Abstract
Robust methods to predict heat transfer are vital to accurately control the blade-tip clearance in compressors and the radial growth of the discs to which these blades are attached. Fundamentally, the flow in the cavity between the co-rotating discs is a conjugate problem: the temperature gradient across this cavity drives large-scale buoyant structures in the core that rotate asynchronously to the discs, which in turn governs the heat transfer and temperature distributions in the discs. The practical engine designer requires expedient computational methods and low-order modelling. A conjugate heat transfer methodology that can be used as a predictive tool is introduced here. Most simulations for rotating cavities only consider the fluid domain in isolation and typically require known disc temperature distributions as the boundary condition for the solution.
This paper presents a novel coupling strategy for the conjugate problem, where unsteady Reynolds Averaged Navier-Stokes (URANS) simulations for the fluid are combined with a series of steady simulations for the solid domain in an iterative approach. This strategy overcomes the limitations due to the difference in thermal inertia between fluid and solid; the method retains the unsteady flow features but allows a prediction of the disc temperature distributions, rather than using them as a boundary condition. This approach has been validated on the fundamental flow configuration of a closed co-rotating cavity. Metal temperatures and heat transfer correlations predicted by the simulation are compared to those measured experimentally for a range of engine-relevant conditions.
Improvement and Validation of an Autonomous Experimental System to Identify BLISK Mistuning
Authors: Denis Sophie , Hoffait Sébastien , Ligot Jérôme , de Cazenove Jean , Salles Loïc 
Published: September 2023

Abstract
This paper presents an autonomous mistuning identification method for single BLISKs. The proposed methodology relies on the ICMM identification methodology. The required inputs are obtained thanks to measurements of the system mode shapes and natural frequencies carried out with a dedicated test rig. The BLISK is excited by an electrodynamic shaker. An infrared Laser Doppler Vibrometer attached to a robotic arm is used to perform the measurements on the blades. The use of a robotic arm enables the reduction of human interventions and significantly limits the positioning error which increases the accuracy of the identification. The proposed setup thus permits to perform repeated characterization campaign, to increase the number of measurements with low human resources cost, and to perform 3D modal analysis. This opportunity makes the test bench suitable for next generation of engines which are composed of one-piece multi-stages compressor, the Bladed druM (BluM). Indeed, the overlay of the blades could reduce the accessibility of vertical measurement.
In this work, the proposed method is firstly presented. The robust experimental input data selection procedure which has been developed and which allows for the optimization of the mis-tuning identification is then described. This procedure reduces the sensitivity of the result with respect to bad experimental content. At last, the usefulness of the method is demonstrated on the 1B and 1T mistuning evaluation of an industrial BLISK.
Integrated Hybrid Air Foil-Magnetic Thrust Bearing (i-HFMTB) Part II: Possibility of Rigid Mode Control for 250HP Air Compressor System
Authors: Lee Yongbok , Ha Yunseok , Kim Jungwan , Jeong Keonwoo 
Published: September 2023

Abstract
This study aims to verify the effectiveness of the 250 HP class compressor system to which the integrated hybrid air foil magnetic thrust bearing (i-HFMTB) proposed in part I is applied, and the vibration and instability problems of air foil journal bearing (AFJB) occurring in the rigid mode are controlled by i-HFMTB. The compressor rotor is supported by two AFJB (journal diameter = 60mm) and an i-HFMTB, and the length and mass of the rotor are 550mm and 15.24kg, respectively. i-HFMTB has a structure in which air foil thrust bearing (AFTB) pads are inserted into eight slotted active magnetic thrust bearings (AMTB), and PD control (proportional gain: 4,000 /differential gain: 10) is applied. The operating area was identified through AFJB’s dynamic coefficients and rotordynamic analysis. As a result with the experiment of the 250 HP compressor system supported only by two AFJB, sub- and super-synchronous vibrations were generated owing to the AFJB’s insufficient load capacity and damping in the rigid mode (7,000rpm) region, and this instability did not disappear even upon increasing the speed to 15,000rpm. However, when i-HFMTB was turned on in rigid mode, it was confirmed that the sub- and super-synchronous vibrations were significantly reduced. The thrust collar tilt angle was calculated through orbit trajectory analysis of the impeller and cooling side, and it was confirmed that the tilt angle of the thrust collar was reduced during i-HFMTB operation. Thus, the coupled moment acting on AFJB could be reduced, this can not only affect the load distribution of AFJB, and but also improve the performance degradation problem of AFTB caused by thrust collar tilt.
sCO2 Bottoming Cycle for Off-Shore Applications – An Optimization Study
Authors: Persico Giacomo , Sanchez David T. , Alfani Dario , Silva Paolo , Vijgen Rene , Ruggiero Marco , Glos Stefan , Le Pierres Renaud , Schmitz Ulrich , Rubycz Rasmus , Cagnac Albannie , Macadam Scott , Orhon Dominique H. 
Published: September 2023

Abstract
Closed Joule-Brayton thermodynamic cycles working with CO2 in supercritical conditions (sCO2) are presently receiving great attention, for their multiple attractive aspects: high energy conversion efficiency, compact size, flexibility of operation, integration with energy storage systems. These features make the sCO2 technology interesting for several energy and industrial sectors, including renewable sources and waste heat recovery.
A further promising area of application of sCO2 systems is bottoming gas turbines in combined cycles, replacing steam. The use of steam implies large-scale components and demands for large space availability for the plant installation. In some relevant applications, such as in off-shore platforms, the lack of space complicates the implementation of steam combined cycles, unless accepting a significant efficiency penalty, along with operation issues related to the necessary use of saltwater as cooling medium as well as the need of continuous supervision by dedicated personnel. In such a context, the combination of gas turbines with sCO2 cycles could open the way for developing new efficient, compact, and flexible combined cycles, potentially suitable for off-shore systems but also attractive for several other sectors which might take advantage from the footprint savings, the enhanced flexibility, and the fast dynamics of sCO2 systems.
In this work we investigate the thermodynamic potential of combining sCO2 cycles with an existing gas turbine for off-shore applications. In particular, we consider a mid-size (25 MW) gas turbine available on the market, and perform a series of thermodynamic optimizations of the sCO2 bottoming cycle in order to maximize the exploitation of the heat discharged by the gas turbine. Systematic optimization strategies are applied to the sCO2 cycle, considering four alternative configurations and including realistic technical constraints, evaluated by leveraging on the most recent technical outcomes from ongoing sCO2 research projects. A comparison is also proposed with a state-of-the-art steam Rankine cycle, in terms of system efficiency and footprint of the main components. The study clarifies the advantages and challenges of applying sCO2 in combination with gas turbines. The comparison with steam technology clearly indicates the relevance of sCO2 systems for off-shore applications and calls for further technical studies in the field.
Entropy Loss Breakdown Comparison for LES and RANS of a Transonic Compressor Stage Midspan Section
Authors: Borcherding Till , Bode Christoph , Rosenzweig Marco , Przytarski Pawel J. , Leggett John , Sandberg Richard D. 
Published: September 2023

Abstract
Further improvements in aero-engine efficiencies require accurate prediction of flow physics, such as shock-boundary layer interaction and incurred loss. The current best-practice of using (U)RANS for such predictions in design iterations can lead to inconsistent loss predictions. To assess where RANS-based approaches produce errors, in this paper we perform a detailed entropy loss breakdown of a modern transonic compressor stage under varying inflow conditions, using the high-fidelity flow field data of the midspan section presented at ASME Turbo Expo 2022 (GT2022-81673, GT2022-82474). From the datasets produced by highly resolved large-eddy simulations the results of this paper will show where loss is generated. Following the loss analysis approach introduced by Zhao and Sandberg (TURBO-20-1017), the entropy transport equation is used to decompose the entropy generation process into different physical mechanisms leading to entropy generation as a representation of loss generation. The introduction of inflow disturbances leads to an increase in stage loss by 23%, mainly caused by the shock and SBLI in the rotor domain. A comparison of LES results with URANS predictions shows that URANS adequately predicts the general flow behavior. However, significant deficits are identifiable in predicting the shock and boundary layer flow near the shock location on the rotor suction side.
Experimental Characterization of a Two Stage Brush Seals: Leakage and Torque Measurements
Authors: Jolly Pascal , Arghir Mihai , Bonneau Olivier , Coirier Rémi , Fiore Giuseppe 
Published: September 2023

Abstract
Two-stage brush seals were experimentally investigated in the present work. The test rig was originally developed to operate with pressurized hot water but was recently adapted also for pressurized air. The brush seals were designed to seal high pressure differences. The bristles are made of Haynes 25 and the rotor is coated with a layer of chromium carbide. Brush seals had identical back and front plates inner diameters, a small fence height and a bristle pack/rotor interference (negative clearance). They were tested for both water and air. The inlet mass flowrates were measured for centered operating conditions while the supply pressure was modified for constant discharge pressure. Water tests were performed for various rotation speeds. The resistive torque, the water temperatures and pressures along the housing were measured. Results are discussed in order to highlight the impact of rotor speed, supply pressure and wear on brush seals performance. In the second part of this work, the results obtained for air are compared to data from the literature, using the equivalent effective clearance. Then, another approach is used for estimating the leakage rate of brush seals by considering the brush as a porous medium. The identified values of the permeability in the Darcy law for air and water are very close. The calibration of the porous medium is then independent of the incompressible or compressible character of the fluid because the velocities through the bristle pack are very small. Moreover, the identified permeability is in agreement with theoretical values. Thus, an accurate estimation of the leakage flow rate of brush seals of similar design can be easily made.
Leveraging Additive Manufacturing to Fabricate High Temperature Alloys With Co-Designed Mechanical Properties and Environmental Resistance
Authors: Pillai Rishi , Ren Q. Q. , Su Yi-Feng , Kurfess Rebecca , Feldhausen Thomas , Nag Soumya 
Published: September 2023

Abstract
A paradigm shift in the traditional sequential design approaches is critically essential to create application-specific hierarchical and multifunctional materials with superior long-term performance for next-generation energy technologies involving extreme environments. In the current work, we aim to leverage the flexibility and geometric/compositional complexity offered by additive manufacturing to demonstrate this new approach by co-designing a compositionally graded Ni-based alloy for molten salts\sCO2 heat exchangers to enable mitigation of environmental degradation of surfaces exposed to molten halide salts, while simultaneously suppressing the consequent deterioration in mechanical stability. Thermokinetic modeling describing the underlying physics of thermally- and environmentally induced spatiotemporal compositional and microstructural evolution will be employed to predict the parameter space of material deposition processes and precisely identify the required composition gradient. Preliminary corrosion and mechanical testing of the dual material demonstrated the potential of the material to replace existing solid solution strengthened materials for this application.
Numerical and Experimental Investigation of Riblet-Coating Impact on Centrifugal Compressor Stage Performance
Authors: Jörg Sophia , Wirsum Manfred , García De Albéniz Mikel Lucas , Leitl Peter , Flanschger Andreas , Kowalik Yvonne , Jenny Philipp 
Published: September 2023

Abstract
Rising energy costs and increasing efforts to reduce greenhouse gas emissions strengthen the demand for highly efficient operation of centrifugal compressors. This applies both to new machines as well as to compressor units with long operation times. One possible measure to reduce drag in flow channels and thus increase compressor efficiency are microstructured riblet-surfaces. Riblets imitate the structure of shark skin and are streamwise aligned grooved surfaces which diminish the viscous drag in turbulent boundary layers.
This paper presents the results of a numerical and experimental investigation regarding the application of riblet structures in centrifugal compressor stages focusing on the aerodynamic performance. Steady-state computational fluid dynamics (CFD) calculations were used for the riblet design in dependence on the design operating conditions. Two different riblet sizes were identified for the application in diffuser and volute. The expected impact resulting from these riblet structures was calculated for compressor design and off-design operation.
Subsequently, the riblet structure was applied on the compressor volute by a dual-cure coating-system consisting of a clear coat, which combines UV-curable resins with aliphatic polyurethanes. To allow for a sufficient accessibility for the manual coating process, the volute was manufactured featuring a vertically split geometrical design.
A closed-loop centrifugal compressor test rig was utilized to investigate the stage performance characteristics at three different tip speed Mach numbers while accounting for tip speed Reynolds similarity. In the scale-model compressor stage, consisting of a shrouded impeller, vaned diffuser and a circular volute, static and total pressures as well as temperatures were measured to quantify the riblet impact. As a main result, the experimental data show an increase in polytropic efficiency of up to 0.5–1.4 %-points for selected operating points based on the riblet coating of the outlet volute. A drag reduction in the volute is indicated leading to lower total pressure losses.
Numerical and Experimental Approaches for Inertial Particle Separator Design
Authors: Saat Ahmet , Işık Halime Esra , Arslan Ahmet , Erdem Erinç , Kaptan Yalın 
Published: September 2023

Abstract
Gas turbine engines, especially turboshaft engines, can be exposed to the unfavourable environmental conditions including ingested sand, dust, rain and salt spray etc. that can cause significant deterioration in engine life and affect its performance. Engine Air Particle Separators (EAPS) fitted to intakes are used for protection of engine parts from the ingestion of foreign particles. Since integrated inertial particle separators (IPS), one of the EAPS’s, have more advantageous characteristics compared with other solutions they are widely preferred. The main aim of this article is to provide insight into the aerodynamic design and performance characteristics of the IPS system using both numerical and experimental approaches. Aerodynamic assessment and particle trajectories have been evaluated through two-way coupled CFD analysis. In addition, the effects of different design such as split area factor, ramp angle, and flow rate on IPS system performance have been investigated. Current study also includes experimental investigation of IPS system test facility based on a sectoral geometry with initial measurement results to validate numerical methodology. During the test campaign, detailed aerodynamic measurements have been conducted and global IPS separation efficiencies have been deduced with different sand types. Results have shown that a very good agreement is observed between the numerical approaches and the test results. Proposed methodology can be considered as an initial part of a well-rounded study to achieve robust IPS system design.
Fluid Dynamic Behaviour of Conventional and Pressure Relieving Brush Seals
Authors: Bowen Joshua P. , Bird Joshua J. , Cross Harry , Jenkins Matthew R. , Bowsher Aaron A. , Crudgington Peter F. , Sangan Carl M. , Scobie James A. 
Published: September 2023

Abstract
Brush seals consist of a static ring of densely packed, flexible, fine wire bristles that provide resistance to the flow. Pressure relieving brush seals can be employed to overcome issues such as hysteresis that affect seal durability by reducing friction between the bristle pack and back plate surface. The impact of such designs on the fluid dynamic behaviour of brush seals was studied following a concomitant methodology that exploited the benefits of both engine representative and large-scale testing facilities. Leakage data were fitted using a porous medium model found in the literature to quantify viscous and inertial resistance coefficients.
Shaft rotation was shown to cause a reduction in seal leakage and an increase in static pressure on the back plate surface. The pressure relieving back plates also resulted in increased static pressures at this location, causing a reduction in flow resistance that increased leakage through the porous bristle pack. Interrogation of the large-scale inter-bristle pressure field for the two back plate designs revealed the distributions of axial pressure diverged towards the rear of the bristle pack. The detail gathered using the large-scale study has been shown to be representative, hence the insight is generically applicable to brush seals.