bluuebunny/crossref_metadata_2025 huggingface dataset:
Ceramic and Metal Additive Manufacturing of Monolithic Rotors From SiAlON and Inconel and Comparison of Aerodynamic Performance for 300W Scale Microturbines
Authors: Badum Lukas , Prochaska Thomas , Schwentenwein Martin , Cukurel Beni
Published: September 2023

The gas turbine industry is continuously developing and testing new materials and manufacturing methods to improve the performance and durability of hot section components, which are subjected to extreme conditions. SiAlON and Inconel 718 are especially desirable for turbomachinery applications due to their high strength and high temperature capabilities. To demonstrate the viability of additive manufacturing for small scale turbomachinery for 300W scale microturbines, a monolithic rotor with a design speed of 450,000 RPM containing radial turbine and compressor was developed considering additive manufacturing constraints. The geometry was manufactured from SiAlON and Inconel 718 using lithographic ceramic manufacturing and selective laser melting, respectively. The additive manufacturing and thermal process parameters as well as material characterization are described in detail. Surface and computerized tomography scans were conducted for both rotors. While the metallic rotor showed undesirable printing artefacts and a large number of defects, the ceramic part achieved a level of relative precision and surface quality similar to large-scale production via casting. To compare turbomachinery performance, an aerodynamic test facility was developed allowing to measure pressure ratios and efficiency of small compressors. The rotors were tested in engine realistic speeds, achieving a compressor rotor pressure ratio of 2.2. The ceramic part showed superior efficiency and pressure ratio compared to the Inconel rotor. This can be explained with lower profile and incidence losses due to a higher fidelity physical representation of the model geometry and better surface finish.
Thermochemical/Thermomechanical Synergies in High-Temperature Solid Particle Erosion of CMAS-Exposed EBCs
Authors: Stokes Jamesa L. , Presby Michael J. , Webster Rebekah I. , Setlock John , Harder Bryan J.
Published: September 2023

Environmental barrier coatings (EBCs) are an enabling technology for the use of SiC-based ceramic matrix composites in next generation gas turbine engines. In the extreme engine environment, EBCs must be able to withstand a variety of individual damage mechanisms and their interactions with each other. Ingested particulates/debris can cause both thermochemical and thermomechanical degradation of EBCs. Siliceous debris primarily based on calcium magnesium aluminosilicates (CMAS) can melt and infiltrate and/or react with EBCs above 1200°C. Similarly, ingested debris can lead to mechanical damage and recession of coatings due to particulate erosion. Both modes of degradation can occur simultaneously during engine operation, and it is crucial to comprehensively understand the mechanisms of coating failure due to high-temperature particulate interactions. This study assesses the erosion durability of Yb2Si2O7-based EBCs exposed to CMAS of various loads in NASA Glenn’s Erosion Burner Rig Facility. CMAS exposures and erosion testing were carried out at 1316°C. The effects of CMAS loading and exposure time on EBC erosion durability were evaluated using Al2O3 as an erodent material.
Modelling of Two-Phase Water Ejector in Rankine Cycle High Temperature Heat Pumps
Authors: Abu Khass Omar , Tran Anh Phong , Klöppel Steffen , Stathopoulos Panagiotis
Published: September 2023

Industrial high temperature heat pumps (HTHPs) can provide carbon-free process heat when operated with renewable energy sources. Using water as the working medium greatly increases the possible range of operation without the detrimental effects of traditional working fluids. One main challenge with this type of heat pump is the high compression ratio required to achieve a given temperature lift. As a result, water based heat pumps need several compression stages. Furthermore, the steam leaving the compressor is highly superheated. Ejectors driven by high pressure condensate allow to de-superheat the steam from the compressor outlet while simultaneously increasing its pressure. Thereby, the required power for compression as well as the number of compression stages can be reduced. This paper studies how the implementation of the two-phase water ejector influences the thermodynamic performance of Rankine cycle HTHP using a thermodynamic model of the ejector. Several cycle architectures are developed to study the ejector integration in the heat pump cycle, including traditional single-stage and multi-stage cycles. The cycles studies are conducted in the Modelica language, in the Modelon Impact environment. The study aims at informing about new developments in two-phase water ejectors and their application potential in Rankine cycle HTHPs. First simulations suggest an efficiency improvement of about 10% through the use of an ejector in the heat pump cycle.
Investigation of the Aerodynamic Interaction Between Rotor and Second Stator in the Large Scale Turbine Rig
Authors: Linne Marius , Ade Dominik , Eitenmüller Johannes , Leichtfuß Sebastian , Schiffer Heinz-Peter , Lyko Christoph , Schmid Gregor
Published: September 2023

This paper presents the results of an investigation of two different interface modeling approaches for Computational Fluid Dynamics in turbomachinery and their influence on the second stator aerodynamics in the 1.5-stage Large Scale Turbine Rig. Highly accurate five-hole probe data as well as oil flow visualizations are used to investigate the aerodynamics within the second stator passage and to validate the numerical results. While unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations appear to be a better qualitative representation of the second stator aerodynamic experiments, the steady-state (RANS) simulation predicts a turbine efficiency that is closer to the experimental data. In both approaches, the boundary conditions, computational domain and turbulence parameters are kept the same. The key difference between the two simulations is the resolution of time and hence unsteady effects. The RANS approach uses a Mixing-Plane interface between stationary and rotating reference frames. Here, unsteady effects of blade row interaction are neglected by mixing flow quantities in the circumferential direction. This affects the development and propagation of the vortex system in the downstream blade row. To account for effects of rotor-stator-interaction and reduce modeling errors, more expensive unsteady simulations are used. In the rotor exit plane, the URANS simulation shows a better match with experimental data, which theoretically should be the more accurate inlet condition for the downstream second stator. Here, unsteady interactions between the vortex systems of the rotor and the second stator lead to an overprediction of the losses in the second stator passage in the URANS compared to the RANS case. Therefore, the overall efficiency is more accurately predicted by RANS.
Combustion Diagnostics and Emissions Measurements of a Novel Low NOx Burner for Industrial Gas Turbine Operated With CO2 Diluted Methane/Air Mixtures
Authors: Babazzi G. , Galeotti S. , Picchi A. , Becchi R. , Cerutti M. , Andreini A.
Published: September 2023

While the employment of Exhaust Gas Recirculation (EGR) is a well-established technique in Internal Combustion Engines to limit NOx emissions, its adoption in Gas Turbine engines hasn’t yet found a practical application due to its expensive and complex installation that doesn’t justify the emissions reduction when compared to already established DLN combustion technologies. EGR becomes an interesting option in GT engines considering the possibility of increasing the CO2 content of the exhaust gases to improve the efficiency of Carbon Capture and Storage (CCS) units. However, the decrease in oxygen content of the combustion air is extremely challenging in terms of combustion stability and therefore of engine operability.

In the present work, a low NOx burner was studied at ambient pressure in a reactive single burner test rig. The burner was fed with methane and characterised in terms of emissions and stability limits at different operating conditions. In addition, the flame position and shape were studied through OH* chemiluminescence imaging together with the flow field thanks to PIV measurements. The effects of CO2 addition on the flame were then investigated at different EGR increasing levels, highlighting the impact of the oxygen content on the combustion reaction intensity. Variations in emissions and burner stability limits in terms of maximum sustainable CO2 content were also studied, to detail the burner operating window. Data have been thoroughly analysed to gather information on the burner behaviour to support the design of new technical solutions capable of ensuring both proper flame stability and low CO and NOx emissions.
Optical Based Emission Monitoring Systems for Combustion Turbine SCR Process Control and CEM Applications
Authors: Himes Richard
Published: September 2023

In parallel with the trend of increasing gas generation, regulatory scrutiny of utility gas turbine emissions is projected to increase as utilities operate their gas turbine fleets dynamically in response to the variability of wind and solar generation resources. While SCR systems have historically provided significant incremental NOx control capability beyond dry low NOx combustor emission levels, associated ammonia injection process control systems are still reliant on extractive based sampling approaches, with up to several minute response time delays. These response time delays in ammonia injection control can lead to time periods of over, or under injection of SCR ammonia during load cycling. In-situ, optical based monitoring systems have the potential to improve SCR process control time response, while also reducing lifecycle operating and maintenance costs associated with NOx/diluent monitoring systems used for SCR process control.

The current paper assesses the accuracy associated with several in-situ optical monitors applied on the stack of a gas turbine combined cycle unit. Moreover, the demonstration explores novel optical monitor configurations for multi-specie measurements that could ultimately reduce the number of measurement paths required for typical continuous emission monitoring (CEM) purposes (e.g., NO, NO2, CO, NH3, CO2, O2 and H2O).

In regard to potential CEM applications, the current paper also examines in-situ optical monitor calibration approaches required under the current CEM regulatory framework, associated issues and measurement configurations that could potentially comply with current CEM quality assurance requirements.
Increased Productivity for Film Cooling Simulations Using Solution-Based Mesh Adaption
Authors: Norman Adam , Arguinzoni Carlo , Pons David , Zori Laith
Published: September 2023

High-pressure turbine blades in a gas turbine experience extreme thermal stress due to the high-temperature flow coming from the combustion chamber. To minimize thermal fatigue and increase durability, the blades can be cooled with an internal and external cooling system. These systems consist of intricate passages that feed a large number of small holes, creating a film on the blade surface. Hole parameters such as the location, pattern, size, and shape must be determined to maximize the cooling effectiveness requiring a large number of design variations.

In the design phase, numerical tools, such as CFD, are employed to quickly simulate design variations and reduce the overall product design phase timeline. The generation of a high-quality mesh for complex blade cooling geometries can be extremely cumbersome and time-consuming. Additionally, knowing precisely where the hot streaks will occur, a priori, is difficult if not impossible. As a consequence, a general over-refinement of the mesh in non-key areas can occur to ensure the flow is properly resolved. This requires extended timelines to mesh and solve cases with large cell counts.

In this work, a methodology is presented that avoids the issue of mesh over-refinement without sacrificing the solution’s accuracy. Solution-based mesh adaption is employed to dynamically add mesh refinement to capture the necessary physics for film cooling simulations. Initially, the methodology is verified on a single-hole configuration cooling a flat plate. This adaption framework is then applied to a standard gas turbine vane to demonstrate the flexibility of the solution-based adaption for any film-cooled geometry. These two cases are compared to mesh-independent solutions to show a reduced time to the solution while maintaining solution accuracy.
Experimental Investigation on Microsecond Pulsed Plasma Supported Biogas Combustion
Authors: Ghabi Ahlem , Boushaki Toufik , Escot Bocanegra Pablo , Robert Eric
Published: September 2023

This paper evaluates the effect of a microsecond pulsed plasma (MPP) on the stabilization and emission characteristics of non-premixed biogas/air flames with various CO2 contents. The MPP is generated by a unique DC-pulsed power generator providing high voltage (HV) pulses over a wide range of pulse repetition frequencies. The burner configuration is made up of two concentric tubes in which a swirler is placed inside the annular part, ensuring the oxidizer’s rotation. The central tube delivers the fuel through an injector placed close to the burner exit. Electrical diagnostics, including voltage, were performed. OH* chemiluminescence measurements were done to describe the structure and stability of the flame. Results showed that plasma generated by microsecond HV pulses can improve flame stability. In this regard, the distribution of key active species in the burner was studied via optical emission spectroscopy (OES). The results revealed that the pulsed plasma generates chemically active species such as excited N2*, CH*, OH* molecules, and H* and O* atoms, thereby improving flame stability. The dependence of the emitted species intensities on plasma parameters was investigated in detail. It is demonstrated that MPP can drastically enhance the dynamic flame stability of swirling non-premixed biogas flames, especially at lean operating conditions. In addition, NOx and CO emissions were studied over a wide range of pulse repetition frequencies. It is seen that the pulsed plasma increases NOx emission slightly and significantly reduces CO concentration in the flue gases.
Reynolds Number Calibration Coefficient for Multi-Hole Pneumatic Probes
Authors: Bachner Johannes , Pahs Andreas
Published: September 2023

The calibration of an additively manufactured cone-shaped five-hole probe is presented for subsonic and transonic flow. The probe has a thermocouple and an additional base pressure hole for transonic measurements. The Reynolds number is varied independently of the Mach number by adjusting the pressure level in a closed test section in three steps. Overall, a Reynolds number range from 3,000 to 20,000 is covered. A significant Reynolds number effect is observed for the pressure coefficients. More than 1,100 test points not contained in the calibration data are evaluated and measurement deviations calculated. The points are distributed over six pressure levels and four Mach numbers. Measurement deviations increase with increasing Reynolds number differences between the calibration and the test points. The Mach number measurement in transonic flow using the base pressure hole is particularly sensitive to the Reynolds number. The root mean square error of the Mach number increases by up to factor of 15 if Reynolds number similarity is not maintained. This demonstrates the importance of Reynolds number similarity when calibrating probes with a base pressure hole. The effect on the flow angles is relatively low with the exception of the radial flow angle in transonic flow. Here, the Reynolds number effect reaches a maximum of 1 deg. A calibration coefficient is proposed that decreases measurement deviations by allowing interpolation between calibration data at different Reynolds numbers and can easily be introduced to most evaluation schemes.
Development and Validation of an Accurate, Minimal-Input Mean-Line Method for the Off-Design Performance Prediction of an Axial Compressor Stage, Using a Compressor-Diffuser Analogy
Authors: Barlin Daniel , Fuls Wim
Published: September 2023

The analysis and performance prediction of gas turbines benefits greatly from the use of one-dimensional mean line modelling, as it can provide reasonably accurate results while requiring fewer geometric inputs and significantly lower computational expenses when compared to higher order methods such as CFD. However, even mean line codes may be limited by the amount of geometric and operational data available, often restricted by Original Equipment Manufacturers for proprietary reasons. This often results in a greater number of assumptions and tuning factors required in order to achieve accurate results. This paper documents the progress in development of a one-dimensional modelling method which requires minimal geometric inputs and tuning factors for analysing the performance of a transonic axial compressor stage, for use in a gas turbine. The minimal input model is achieved through an analogous modelling methodology, whereby the stage’s rotor and stator rows are modelled as simple diffusers with flow areas approximately equal to those in the compressor stage. A design point calibration operation is performed to estimate all diffuser flow path areas using a set of industry-knowledge-based assumptions, and blade angles are estimated using widely adopted correlations from open literature. The estimated geometries are then used as inputs for an off-design numerical model. An area correction factor calibration is required to better match the pressure ratio performance map. The model was validated against four well documented NASA axial compressor stages with good agreement. The modelling methodology presented an efficient means of predicting compressor stage pressure ratio performance with acceptable accuracy while requiring minimal inputs. Further work is still required to improve the loss characteristics such that the work and efficiency prediction accuracy is improved.
Effect of Fuel Reactivity and Operating Conditions on Flame Anchoring in the Premixing Zone of a Swirl Stabilized Gas Turbine Combustor
Authors: Tartsch Simon , Flebbe Saskia , Marques de Sousa Ponte Germano J. , Sattelmayer Thomas
Published: September 2023

Flashback with subsequent flame anchoring (FA) is an inherent risk of lean premixed gas turbine combustors operated with highly reactive fuel. The present study has been performed to characterize flame stabilization in the premixing zone of a lean premixed swirl stabilized burner and to identify critical combustion characteristics. An optically accessible burner was used for experimental investigations under atmospheric pressure and elevated preheat temperatures. The air mass flow rate, global equivalence ratio and preheat temperature were systematically varied to identify critical operating parameters. Hydrogen-natural gas mixtures with hydrogen mass fractions from 15 to 100 % were studied to evaluate the impact of fuel reactivity. The air-fuel mixture was ignited with a focused single laser pulse to trigger FA in the premixing zone during steady operation. High speed imaging with OH*-chemiluminescence were applied to observe flame characteristics and evaluate flame anchoring propensity. Flame anchoring limits (FAL) are reported in terms of the minimum global equivalence ratio at which the flame was blown out of the premixing zone within a critical time period. A comparison of characteristic time scales at FAL shows that the main impact during flame anchoring is given by the fuel reactivity and to some ex tent by preheat temperature. A Damköhler criterion is derived from the FAL that allows prediction of FA propensity based on operating conditions and 1-D reacting simulations.
Influence of Turbulence Modeling on the Simulation of Miniaturized Levitating Centrifugal Pumps for Cardiac Assistance
Authors: Gil Antonio , García-Tíscar Jorge , Quintero Pedro , Mares Andrea
Published: September 2023

Due to the limited availability of compatible heart donors, one of the most promising treatments for patients suffering from cardiac insufficiency is Mechanical Circulatory Support using Left Ventricular Assist Devices (LVAD). The main device in the market, HeartMate3, is a low size centrifugal pump incorporating a magnetic levitation system. This device assists the ventricle in generating the needed pressure head to provide the required cardiac output of blood flow through the circulatory system. However, the blood within an LVAD experiences a wide range of non-physiological phenomena such as high shear stresses and device-induced turbulence. Although there are multiple references approaching the behavior of these devices both experimentally and numerically, hardly any of them has analyzed the influence of turbulence modeling on the quantification of performance variables. Furthermore, the performance of LVAD must be evaluated through all possible working conditions. Therefore, the current work presents a set of Unsteady Reynolds-Averaged Navier Stokes and Large Eddy Simulations of the HeartMate3 operating under various conditions. Both the hemodynamic performance and the hemocompatibility of the device are considered. In addition, a 0D Windkessel model is imposed at the outlet to account for the resistance and compliance of the vascular system downstream of the device.
Experimental Investigation of High Frequency Flame Response on Injector Coupling in a Perfectly Premixed Multi-Jet Combustor
Authors: Rosenkranz Jan-Andre , Sattelmayer Thomas
Published: September 2023

High frequency injector-coupled thermoacoustic instabilities are a major threat to multi-jet combustors in rocket and gas turbine engines. The complex three-dimensional acoustic coupling between the combustion chamber and injector acoustics cause local fluctuations in heat release. In turn, multiple thermoacoustic feedback mechanisms close the thermoacoustic loop and serve as a source of the thermoacoustic instability. Except for the flame deformation and flame displacement mechanism, the underlying feedback mechanisms for high frequency instabilities are to a large extent unknown. The paper at hand gives new insights into the injector-coupled convective driving mechanisms that are present in multi-jet combustors at perfectly premixed conditions. The forced flame response to the first transverse combustor mode is investigated for two distinct injector tube lengths: one with an axial acoustic velocity node and one with a velocity anti-node coupling at the injector-combustor interface. Phase locked OH* images reveal convectively transported coherent vortex structures as the main source of the flame response. The origin of the flame response can be linked to the axial acoustic velocity at the injector-combustor interface using numerical simulations. Both configurations show a positive Rayleigh Integral and a clear oscillation of the heat release fluctuations in-phase with the acoustic pressure fluctuations over the full period. In similarity to time delay models in low frequency thermoacoustics, a wave number model is proposed to estimate the local flame response due to feed flow modulations and validated with the experimental results.
Effects of the Seal Wire on the Nonlinear Dynamics of the Aircraft Engine Turbine Blades
Authors: Tüfekci Mertol , El Haddad Fadi , Salles Loïc , Setchfield Richard , Renson Ludovic
Published: September 2023

Complicated systems made of multiple components are known to be difficult to model, considering their solutions can change dramatically even with the slightest variations in conditions. Aircraft engines contain such complicated systems, and some components in aircraft engines’ turbines can cause significant changes in the system’s overall response. Hence, this study is focused on investigating the behaviour of a turbine blade of an aircraft engine and the effects of the contact between the blade and the seal wire on the dynamics of the blade-disc system. The investigation is performed via various numerical simulations in time and frequency-domains. One sector of the bladed disc is modelled using the finite element method with the lock plate and the seal wire imposing cyclic symmetry boundary conditions in the static, modal, and frequency-domain forced response analyses. In time-domain analyses, the cyclic symmetry is replaced with simplified displacement restricting boundary conditions. The time-domain analysis contains steady-state forced responses of the system. The results show that contact with the seal wire is not a major source of nonlinearity and damping. The contacts with the lock plate contribute more to the vibration damping than the seal wire. However, compared to the contacts at the root of the blade, both components remain less significant with regard to frictional damping and nonlinearity.
A New Concept for Improving the Efficiency of Gas Turbines for Power Plant Operation
Authors: Sunkler Rupert , Stalder Jean-Pierre
Published: September 2023

A method for enhancing the efficiency and power output of gas turbines is presented here. The concept relies on increasing the machine’s pressure ratio without modification to the existing baseline Brayton cycle by adding independent topping gas generators in parallel. The mass flow through the compressors of the topping gas generators is higher than the baseline cycle. This additional mass flow is bled off from the topping compressors to do work through an external air expander. The conditions in the baseline cycle turbine remain unaffected.

These topping gas generators are envisioned as being installed in place of the existing combustor(s), acting as high-pressure compressor and turbine, with the original GT compressor and turbine acting as their low-pressure counterparts. The air mass flow after the low-pressure compressor is divided into several parallel partial flows, which are fed to the gas generators. The gas generators consist of a compressor (in most cases a 1-stage centrifugal compressor will suffice), combustion chamber and turbine. They are, as a matter of fact, dimensionally small high-speed gas turbines that are free-running, like turbochargers or like the HP-section of aero engines.

The concept can be applied to both new gas turbine designs and retrofits, resulting in increased power output and thermal efficiency. The paper describes the concept and presents sample calculations with various gas turbine types, indicating the possible achievable benefits under various assumptions.
GPU-Accelerated High-Fidelity Rotating Detonation Engine Simulations Using an Extended Flamelet Progress Variable Approach
Authors: Shunn L. , Ham F. , Elasrag H. A. , Hoke J. , Schumaker S. Alexander
Published: September 2023

A fast approach is introduced to aid the evaluation and design of rotating detonation engines (RDEs) using large eddy simulation (LES). The new approach implements an extended flamelet progress variable model in the GPU-accelerated charLES CFD solver from Cascade Technologies. In the extended flamelet approach, tabulated reaction rates from unstretched laminar premixed flames are parameterized and scaled to describe the high-pressure detonation conditions in RDEs. The reaction rate scaling parameters are trained using Zeldovich-von Neumann-Döring (ZND) detonation solutions over a wide range of operating conditions. Sensitivity analysis is performed to assess the impact of the regression algorithm and best-fit scaling parameters on the reconstructed reaction rates. The method is applied to LES of the AFRL 6-inch rotating detonation engine with non-premixed injection of hydrogen in air. The GPU-resident charLES solver demonstrates speedup of almost two orders of magnitude compared to conventional CPU-based solvers and achieves turnaround of high-fidelity RDE simulations in less than one day on modest GPU resources — a critical threshold to enable the use of LES within a design cycle. The combination of reduced-order flamelet modeling and efficient GPU acceleration makes the overall approach a viable candidate for design exploration and optimization of practical RDEs.
Complete Engine Soak-Back Using Coupled Lattice-Boltzmann and Nodal Network Simulations
Authors: Popescu Stefan , Burkia Alessandro , Mech Thomas , Zapata Alexandre , Combébias Sebastien
Published: September 2023

Numerical methodologies have been developed for a number of years, in order to predict engine soak-back in earlier design stages. This current paper is the second phase of a methodology development using coupled lattice-Boltzmann and nodal network simulations for the prediction of soak-back of a helicopter engine and its engine bay. The previous phase of the study (see GT2020-16096) focused on the engine bay, simulated with lattice-Boltzmann methods, whereas the core flow was simply modeled with imposed Heat Transfer Coefficients (HTC) and temperatures. Conduction and radiation within the solid parts are solved by a thermal solver, coupled with the CFD solver calculating convective heat transfers.

The current phase presented here extends the previous methodology by increasing the complexity of the core flow modeling. Two additional numerical approaches are considered: (1) a full simulation of the engine core flows and engine bay using lattice-Boltzmann simulations, and (2) a coupled methodology between lattice-Boltzmann simulations (for the engine bay) and 3D nodal network (for the core flows).

On one side, this study compares numerical predictions to tests data when available. On the other side, the numerical methodologies are compared using more detailed flow analysis and solid temperature evolutions, together with simulation turnaround times. All methodologies show promising results that could improve current industrial development processes.
Experimental Investigation of a Large Tilting-Pad Journal Bearing With a Direct-Bonded Sub-Millimeter PEEK Lining
Authors: Stottrop Michael , Engels Alexander , Weißbacher Christoph , Bender Beate
Published: September 2023

A novel coating technique allows direct bonding of polymer material to large plain bearings, enabling lower-cost manufacturing, more flexible running layer design and thin-layer coatings. In this publication, experimental results for a 500 mm tilting-pad journal bearing (TPJB) with a direct bonded sub-millimeter polyether ether ketone (PEEK) lining are presented. The five-pad TPJB in a non-flooded design is investigated on a test rig for original sized turbine bearings over a speed range of 1000 rpm – 3600 rpm. With the test rig, fluid film pressure and the distance between the shaft and the pads backing are measured from the rotating and axially shiftable shaft. By knowing the permittivity of the PEEK material and the thickness of the liner, the fluid film thickness is calculated from the data of a capacitive distance sensor. The experimental data are compared with those obtained with an identical bearing with Babbitt as lining material.

The results show markedly lower pad backing temperatures for the PEEK lined pads than for the Babbitt-lined pads and a reduction in their axial deflection is detected with the PEEK lined pads. Therefore, the test bearing can be loaded up to 4.75 MPa (at 3000rpm) in the experiments.
Numerical Investigation of the Interaction of a Circumferential Groove Casing Treatment and Near-Tip Modifications for a Highly-Loaded Low-Speed Rotor Under the Influence of Double Leakage
Authors: Reisinger Lukas , Eckel Jannik , von Jeinsen Philipp , Gümmer Volker
Published: September 2023

In [1], Eckel et al. proposed using a convex-profiled pressure side region close to the tip, known as belly, as an effective method of extending the operating range of low-speed axial compressor rotors. In the literature, circumferential grooves are another well-described technique for improving the stable working range of a compressor rotor. No research has been conducted to date to determine which modification is more effective and how they interact when used together.

This paper numerically investigates the influence of circumferential casing grooves and near tip modifications on the flow field in the tip region of a highly-loaded, low-speed axial compressor rotor. The simulated rotor consists of a hybrid blade configuration with a tandem profile in the mid-span region and single blade profiles near the endwalls. The single blade profile close to the tip features three different convex-profiled elements, which differ in their respective thicknesses. The aim of the numerical analysis is to explain the interaction of the secondary flow phenomena when applying the circumferential grooves and the belly geometries. For this purpose, eight different axial positions of the circumferential groove are investigated for each of the three belly configurations. These are arranged in 10 % increments from −7 % to 63 % along the axial rotor tip chord. The potential of the concept is evaluated by a numerical investigation in the 1.5-stage setup with an inlet guide vane and tandem stator.

It is shown that a circumferential groove can further increase the operating range for all belly configurations when positioned axially correctly. In this respect, equalization of the near-casing deceleration in the circumferential direction leads to an extension of the stall margin with both modifications. Concentrated regions of low momentum fluid with a large extent in radial direction should be avoided consequently. A tip vortex stability factor is introduced to quantitatively evaluate this effect. The operating range can thus already be estimated in a first approximation at the design point.

In general, the groove and belly should be positioned where the tip leakage vortex meets the pressure side of the adjacent blade. If the groove is used together with the belly, the leading edge of the former should be situated at the location of maximum thickness of the near tip modification. The effects of the circumferential groove and the belly are then superimposed. If using only one modification, the belly appears better suited for ensuring an extension of the operating range while maintaining high efficiencies.
Dynamic Modeling and Degradation Study of a Hybrid Electric Power System for Urban Air Mobility
Authors: Donateo Teresa , Ficarella Antonio , Spada Chiodo Ludovica
Published: September 2023

This investigation presents a model-based degradation study of a Hybrid Electric Propulsive System in parallel configuration for Urban Air Mobility. Literature studies on hybrid-electric aircraft are mainly devoted to the sizing and the management of hybrid systems and the energy flows are usually analyzed with a steady-state model applied to each flight phase while the role of hybridization in supporting the engine during transients has been only hinted at. In fact, the faster response of the electric drive can be used to stabilize the rotor shaft so that the dynamic response of a hybrid electric powertrain is quite different from a conventional configuration. To this scope, a complete model of the power system including the coaxial rotors, the mechanical connection, the turboshaft engine, the electric motors, and the battery is used in the present investigation. The inputs of the model are the pilot commands and the speed components of the rotorcraft. The model is used to highlight the degradation of the dynamic response as a consequence of component deterioration, with different degradation criteria, both on the thermal and the electric path. The results obtained in this work revealed how the torque contribution of the electric machine not only reduces fuel consumption and improves the dynamic response of the powertrain as already known in literature but also reduces the effect of engine deterioration on the performance of the power system. The outcome of the investigation is a dataset useful to train machine learning algorithms for the diagnostics and prediction of the state of health, especially considering the lack of experimental data in this field.
Optimized Casing Treatment to Improve Stall Margin Under Circumferential Pressure Distortion in a High-Speed Axial Flow Fan
Authors: Li Yihan , Li Jichao , Du Juan , Liu Yang , Zhang Min , Zhang Hongwu
Published: September 2023

Aviation fans often suffer from the negative effect of distorted inflow on the stall margin. An effective way to solve the aforementioned problem is to apply casing treatment for extending the stall margin. However, previously, it was observed that casing treatments often increase the stability but with reduced efficiency. Therefore, an optimized axial slot casing treatment (OPCT) was designed that improves the stall margin by 7.31% with 1.97% efficiency gain at a design speed of 100% in a high-speed axial flow fan. The stability-enhancing effect of the OPCT under distorted inflow was further evaluated. Based on the airworthiness standard, the distorted inflow with 9% of composite distortion index was tested with OPCT. At 100% design speed, the OPCT can still improve the stall margin by 6.19% with an improvement in efficiency by 1.63%. The stall margin improvement due to the OPCT at 80% design speed can be up to 13.31% with an improvement in efficiency by 0.87%. The unsteady measurement results under distorted inflow indicate that the location of the shock wave obviously moves forward towards the blade tip leading edge as the rotor blade rotates out of the distorted region. This in turn leads to an earlier stall of the fan compared to that at uniform inflow. When the OPCT is applied, although the fluctuation of the tip leakage vortex in the slot region is stronger than that in smooth casing, the strength of the interaction between the shock wave and tip leakage flow can be suppressed, and the location of the shock wave at the distorted region is pushed back towards the blade passage by the OPCT. Consequently, the transition from the disturbance downstream of the distortion region to the stall inception is postponed. It was experimentally discovered that the casing treatment does not alter the instability mode of the fan, and the fan eventually surges, which is consistent with B parameter value of 2.942. However, under the distorted inflow, B parameter can be reduced from 2.942 to 0.863, and thereby, the instability mode of the fan is changed from surge under uniform inflow to stall under distorted inflow. The aforementioned phenomena can guide the instability prediction when the fan encounters distortion or casing treatment is applied in future studies.
Non-linear Regression Model for Fitting Experimental Emissions Data
Authors: Ahrens Denise , Traub Sebastian
Published: September 2023

The measurement and reporting of non-volatile Particulate Matter (nvPM) emissions is now integral to aircraft engine emission certification. Akin to other gaseous emissions, CAEP11 sets a new LTO based standard. So far, the question how nvPM emission can be corrected for ambient conditions has to remain open. Addressing this, combustor rig tests may be consulted, where performance parameter such as Air-to-fuel ratio, pressure and temperature can be varied independently. However, results from selected tests may be misleading as nvPM emissions may show measurement uncertainties within actual sensitivities. The paper provides a novel approach utilising experimental data to investigate the prevailing sensitivities at different operation conditions and derive applicable correction factors. This methodology makes use of the fundamental assumption that each change measured in nvPM emissions is explainable with the relative change in combustor AFR, the combustion chamber inlet pressure P3, and combustor inlet temperature T3, for a given combustor design running on the same fuel. Computing the relative changes between all measurements of the same test for all performance and emission parameters enables the fitting of a nonlinear regression model to the experimental data. The fitted function consists of the product of the relative change of the performance parameters to the power of polynomial exponents. The methodology has the potential to be applied to a wide variation of emissions data obtained from different sources as combustor rig tests as well as from engine emission tests. The paper concludes with a first application of the methodology to experimental engine emissions data and a short discussion on AFR sensitivity. In order to set-up a more broadly applicable model nvPM pathways and mechanisms and their dependencies must be better understood helping to identify relevant parameters, e.g. characteristic AFR in the nearfield of the fuel spray nozzle.
Historical Developments in Fan Technologies for Aeroengines
Authors: Benini Ernesto , Mistry Chetankumar , Wadia Aspi R.
Published: September 2023

This paper reports on the evolution of fan aerodynamics starting with turbofan engines featuring moderate by-pass ratios (between 4 and 6) up to Ultra-High-By-pass-Ratio (UHBR) configurations which are currently being developed. The implementation of key enabling technologies for fan blades are discussed from a historical perspective, spanning from high-aspect ratio fan blades with part span shrouds (or snubber) to wide chord fan blades, from un-ducted (UDF) and propfan open rotors to highly swept blades. With continuous requirements for higher thrust and lower fuel consumption, bypass ratio demand has also increased leading to UHBR configurations (by-pass ratios higher than 13). Almost all engine companies have responded to these challenges by reducing the number of fan blades. To meet future performance and stability requirements of lower fan pressure ratios, new fan architectures are discussed.
Annular Liquid-Film Fragmentation Process Sheared by Developed Turbulent Gas Flow
Authors: Kamada Yoshiaki , Inoue Takuya , Wang Zhenying , Inoue Chihiro , Senoo Shigeki
Published: September 2023

Erosion by water droplets is a critical issue in steam turbines, but the detailed process is still unclear. In the present study, we investigate experimentally the sequential steps of liquid sheet instability when subjected to a developed turbulent gas stream, followed by droplet fragmentation. To control the boundary-layer thickness of the turbulent gas flow that determines the thin water-film instability, we employ a pipe flow. The liquid sheet slowly propagates along the inner wall and the gas flows at speeds of up to 100 m/s in the center. The liquid sheet sheared by the turbulent gas flow destabilizes intensely owing to both Kelvin-Helmholtz (KH) and Rayleigh-Taylor (RT) instabilities. At the trailing edge of the pipe, of thickness of 2 mm, the sheet stagnates. Liquid ligaments then elongate in the axial direction, which eventually disintegrate into droplets.

We construct a theoretical model describing the liquid-film instability, the properties of the ligaments, and the droplet size dispersed downstream. The circumferential wavelength at the trailing edge is determined by the RT instability, which is accelerated by the shear force of the gas flow and gravity. The ligament diameter is determined by the conservation of flow rate. We show that the droplet size dispersed downstream can be predicted from the diameter of the ligament. We also indicate the validity of this theory based on our experimental results and demonstrate its application to a practical condition.
Film Cooling Effectiveness and Flow Structures of Butterfly-Shaped Film Cooling Hole Configuration
Authors: Jeong Jin Young , Jo Ye Rim , Kang Min Seok , Kang Young Jun , Kwak Jae Su
Published: September 2023

Film cooling is applied to various high-temperature components of a gas turbine and greatly affected by the shape of the injection hole. Numerous studies have been conducted to investigate various film cooling structures to increase the film cooling effectiveness by inducing coolants toward the surface. In this study, a butterfly-shaped film cooling hole configuration is proposed, which consists of a pair of asymmetric fan-shaped holes installed adjacently. This novel structure enhances film cooling effectiveness by utilizing the interaction between coolant jets from the asymmetrical film cooling holes.

In this study, the film cooling effectiveness of the butterfly-shaped hole configuration was experimentally characterized under low-speed conditions on a flat plate, and was compared with that of widely used fan-shaped holes. Also, a numerical study was conducted to understand and visualize the flow structures generated by the butterfly-shaped film cooling configuration. As a result, an anti-vortex structure was observed near the hole exit. The film cooling effectiveness of the butterfly-shaped hole configuration was also compared with that of the fan-shaped hole. The film cooling effectiveness of the butterfly-shaped hole configuration was 1.9% higher than that of the optimized fan-shaped film cooling hole at its optimized condition. It was also found that the film cooling effectiveness increased with the blowing ratio for the butterfly-shaped hole configuration. It is expected that the film cooling effectiveness can be further improved by adjusting the shape parameters of the butterfly-shaped hole.
Vibro-Acoustic Responses and Pressure Signal Analysis for Early Surge Detection in a Turbocharger Compressor
Authors: Silvestri Paolo , Niccolini Marmont Du Haut Champ Carlo Alberto , Reggio Federico , Ferrari Mario Luigi , Massardo Aristide Fausto
Published: September 2023

High-speed centrifugal compressors may be exploited to pressurize fuel cell systems. Nonetheless, due to fuel cells significant interposed volumes, compressor behavior can lead to severe vibrations related to fluid-dynamic instabilities during part load operating conditions. In particular, surge strongly limits centrifugal compressors’ stable operating region when moving towards low mass flow rates due to a change in system working point. Therefore, compressor dynamic response must be adequately characterized for early surge detection. To this aim, a dedicated experimental activity was conducted on a vaneless diffuser turbocharger coupled to a solid oxide fuel cell emulator plant; compressor evolution towards surge was investigated. Several signal processing techniques were applied to pressure signals as well as vibro-acoustic responses to better predict compressor behavior and classify its status as stable or unstable.

Cepstrum, cross-correlation and wavelet transform have been identified as suitable techniques to define precursors able to detect incipient surge conditions early. By means of cross-correlation function, propagation phenomena in the ducts can be investigated to assess how they interact near compressor low-mass flow rate unstable conditions. Cepstrum provides a convenient way to determine pressure signal spectrum distortion in terms of further periodic components onset; they may be due to complex system responses generated by transient phenomena; indeed, it allows identification of hidden anomalous contributions in system response which may arise in incipient surge conditions. Wavelet transform was performed on both structural and pressure response signals to observe their dominant energy contents temporal evolution; indeed, such spectral pattern time-dependent variation can detect the rise of unstable conditions.

By doing so, a complete system identification is performed which allows a deeper investigation of the physical phenomena involved; moreover, a more complete set of surge precursors extracted from different probes’ physical signals were defined. The results obtained provide original diagnostic insights for monitoring systems suited to perform early surge detection. Indeed, compressor instability prevention can extend its operating range, performance, and reliability to allow better integration with other plant components. Finally, cepstrum application for compressor instability identification can be regarded as a novel method in the fluid machinery field.