bluuebunny/crossref_metadata_2025 huggingface dataset:
Thickened Flame Model Extension for Dual Gas GT Combustion: Validation Against Single Cup Atmospheric Test
Authors: Meloni Roberto , Babazzi Giulia , Giannini Nicola , Castellani Simone , Nassini Pier Carlo , Picchi Alessio , Galeotti Sofia , Becchi Riccardo , Andreini Antonio
Published: August 2024

The development of predictive combustion models is more and more strategic in the design definition of gas turbine combustor. The Thickened Flame Model (TFM), despite its high computational cost, is one of the most accurate approach available in literature since it can naturally take into account the non-equilibrium effects into the flame brush (i.e., strain and heat losses) as well as preferential diffusion when hydrogen is employed. Conversely, the original formulation of this combustion model needs several adjustments to accommodate the properties of the mixture when different streams of fuels and/or oxidizers are present in the system.

The present work represents a first step in the extension of this combustion model to handle multiple streams of fuels and oxidizers. More specifically, an industrial burner fed with two different fuel streams and air as oxidizer is considered. The pilot fuel line is fed with micro hydrogen injections with the aim to enhance the lean blow-out margin, while the main one with pure methane. Dedicated tests are performed at the THT laboratory (University of Florence) to retrieve the main information characterizing the burner (emissions, temperature and pressure pulsations) as well as OH* chemiluminescence for the flame shape and position at the same operating conditions.

The comparison between the numerical results and the experimental data will provide highlights about the ability of the extended-TFM to capture the main features of the flame stabilization mechanisms.
Impacts of Material and Machine on the Variation of Additively Manufactured Cooling Channels
Authors: Altland Abbigail Y. , Corbett Thomas M. , Thole Karen A.
Published: August 2024

While additive manufacturing (AM) can reduce component development time and create unique internal cooling designs, the AM process also introduces several sources of variability, such as the selection of machine, material, and print parameters. Because of these sources, wide variations in a part’s geometrical accuracy and surface roughness levels can occur, especially for small internal cooling features that are difficult to post-process. This study investigates how the selection of machine and material in the AM process influences variations in surface quality and deviations from design intent. Two micro-scale cooling geometries were tested: wavy channels and diamond-shaped pin fins. Test coupons were fabricated with five different additive machines and four materials using process parameters recommended by the manufacturers. The as-built geometry was measured non-destructively with computed tomography (CT) scans. To evaluate surface roughness, the coupons were cut-open and examined using a laser microscope. Three distinct roughness profiles on the coupon surfaces were captured including up-facing, down-facing, and channel walls built at 90 degrees to the build plate. Results indicated that both material and machine contribute to producing different roughness levels and very different surface morphologies. The roughness levels on the down-facing surfaces are significantly greater than on the up-facing or sidewall surfaces. Geometric analysis revealed that while the hydraulic diameter of all coupons was well captured, the pin cross section varied considerably. Along with characterizing the coupon surfaces, cooling performance was investigated by experimentally measuring friction factor and heat transfer. The variations in surface morphology as a function of material and machine resulted in heat transfer fluctuating by up to 50% between coupons featuring wavy channels and 26% for coupons with pin fin arrays. Increased arithmetic mean surface roughness led to increased heat transfer and pressure drop; however, a secondary driver in the performance of the wavy channels was found to be the roughness morphology, which could be described using the surface skewness and kurtosis.
Investigating the Unsteady Dynamics of a Multi-Jet Impingement Cooling Flow Using Large Eddy Simulation
Authors: Morsbach Christian , Matha Marcel , Brakmann Robin G. , Tabassum Sadiya , Bergmann Michael , Schroll Michael , Willert Christian , Kügeler Edmund
Published: August 2024

We investigate the unsteady behavior of an in-line jet impingement array of nine jets at a Reynolds number of 10 000 in a narrow channel subjected to a developing cross flow of up to 25% of the bulk jet velocity. To this end, we present an improved version of a previously published large eddy simulation (LES) now with resolved turbulence at the inflow boundaries. After a careful analysis of the transient behavior and statistical convergence of the LES, we discuss the time-averaged heat transfer characteristics of the configuration compared to numerical references of similar configurations. We then show how the large-scale unsteadiness increases from jet to jet. Both space-only and spectral proper orthogonal decompositions (POD and SPOD) are used to discuss the large-scale organization of single jets and multiple jets in combination. The latter shows a qualitative change in the unsteady behavior of the temperature footprint on the impingement wall with increasing cross flow.
High Speed H2 Centrifugal Compressor: a General Review of Journal Bearing Design and Experimental Validation
Authors: Vannini Giuseppe , Giannelli Carolina , Matina Dario , Cangioli Filippo
Published: August 2024

Hydrogen (H2) service is an emerging trend of Energy Transition, and centrifugal compressors will be effectively used to support the H2 production and transport chain. From a Turbomachinery design viewpoint, H2 compression yields many technical challenges spanning almost all the engineering disciplines involved (e.g., thermodynamics and materials, to name but a few) and this paper is focusing on the rotordynamic aspects and bearing design.

For this compression service, stacked rotor technology is used, which allows a higher impeller tip speed, and thus a higher compressor head, to be achieved with the same machine size and mechanical limitations of the rotor material compared to a conventional shrink fit assembly. From a rotordynamic and bearing design perspective, the main implications of achieving a high rotor peripheral speed are:

• Increased rotor flexibility: the rotor transitions through many rotor modes before reaching the operating speed, and they must be adequately damped.

• High journal surface peripheral speed: this must be managed from both thermal and rotordynamic viewpoint.

To meet the applicable design requirements based on API 617, the Authors adopted Flexure Pivot journal bearings with Integral Squeeze Film Dampers.

This paper shows, through a dedicated rotordynamic study, how the Flexure Pivot journal bearing with Integral Squeeze Film Dampers enable a rotodynamic design that fully complies with the requirements and moreover offers some new experimental data to confirm the validity of the design.

Finally, the paper shows how this bearing technology is ready to support even the next generation of H2 compressors, in which the peripheral speed of the rotor will be further increased using new higher strength materials.
A Literature Review on Data Sources and Methodologies for Enriching Gas Path Analysis With Earth Observation Data
Authors: Seume Erik , Göing Jan , Friedrichs Jens
Published: August 2024

Aero engine performance and condition deterioration are a function of operational severity. Operational severity is determined by various aspects such as airborne contaminants, derates, ambient temperature, humidity, and precipitation. More severe operating environments induce cost, which should be managed by using earth observation (EO) data in engine health monitoring. This paper presents an analytical approach that incorporates a broad set of EO data into engine health management and subsequent maintenance planning. Current approaches to gas path analysis are extended by incorporating EO data. The analytical approach is presented in combination with a literature review. The literature review covers the following topics: flight trajectory modeling, EO/environmental condition data, as well as engine performance, condition, and deterioration modeling. Methods and data sources in these different areas are reviewed while simultaneously presenting the currently researched analytical approach. The researched analytical approach creates high-resolution contamination profiles for a flight trajectory on a global scale. Weather conditions and the ingestion of aerosols and sand are monitored and correlated with aero engine condition and performance. A wide range of data sources are presented, which however only partly cater to the needs of the Maintenance, Repair and Overhaul community.
Lattice-Boltzmann Modelling of Internal Compressible Flows: Application to the Transonic LS89 Cascade
Authors: Tsetoglou Iason , Zhao Song , Jacob Jérôme , Boivin Pierre
Published: August 2024

In this work the D3Q19 Hybrid Recursive Regularized Pressure based Lattice Boltzmann Method presented by Farag et al. (2021) is assessed for the simulation of complex transonic internal flows. A Lattice Boltzmann solver presented by Jacob et al. (2018) treating the mass and momentum conservation equations is coupled with a finite volume scheme for the resolution of the conservative form of the total energy equation as shown by Zhao et al. (2020), leading to a fully numerically conservative scheme. The well documented case of the high-pressure turbine guide vane cascade with the VKI LS89 profile is examined. To the authors’ knowledge, this is the first numerical aero-thermal investigation of this configuration using a Lattice Boltzmann approach. An appropriate numerical domain along with a grid refinement technique are used to accommodate a Cartesian grid while ensuring flow periodicity downstream of the cascade in the pitch-wise direction. This is verified thanks to the time-averaged profiles of the exit isentropic Mach number and exit isentropic Reynolds number. The solid boundary is introduced in the Cartesian grid with a cut-cell immersed boundary technique where the boundary nodes of the domain are outside of the solid. An efficient treatment for these nodes is used to accurately represent the near wall flow dynamics. An explicit power-law velocity wall model is used to accurately predict the near wall velocities. A logarithmic temperature wall function is also added to this method to improve the convective heat transfer estimation on the blade surface. The results of this study are compared to experimental and numerical results found in literature, proving the LBM to be a viable approach for compressible internal flows.
Phase Prediction Methodologies for Rapid Screening of High Entropy Alloys
Authors: Mohammadi Aron , Tsang Jonathan , Huang Xiao , Kearsey Richard
Published: August 2024

Increasing gas turbine hot section temperatures is a venue to improve fuel efficiency, thus pushing the need for new, higher temperature resistant materials. Experimental results show that high entropy alloys (HEAs), consisting of near equiatomic amounts of various metallic elements with no clear solvent, exhibit excellent high temperature mechanical properties, corrosion resistance, and good strength to weight ratios. This has resulted in significantly increased interest in studying HEAs for potential gas turbine application over the past decade. The properties of HEAs tend to be highly sensitive to phase composition; however, pre-existing phase prediction methodologies used for traditional alloy compositions, with a clearly defined solvent, are generally not well suited to HEAs. Additionally, the combination of the vast design space and complex elemental interactions render experimental exploration of new HEAs unfeasible at scale, necessitating higher throughput methods. Computer aided calculation of phase diagrams and first principal calculations are well established methods for predicting the phase structure of hypothetical alloy compositions, however they tend to be very computationally intensive and thus their speed is highly limited by available hardware. Two prediction methods capable of rapidly screening candidate composition are empirically developed design parameters based on values derived from the elemental composition of the alloys and machine learning models trained using available experimental HEA phase compositions. This simplifies the calculations and the input parameters required for both methodologies are readily available. This work compares the effectiveness of a variety of empirical design parameters and a pre-trained machine learning model, based on a convolutional neural network architecture, at predicting the resultant phases in various HEA compositions, including the W-Nb-Mo-Ta-Ti-Zr alloy system.
Development of a Novel Hydrogen Burner Using Additive Manufacturing
Authors: Kim Shaun , Kim Jupyoung , Byun Hosung , Ku Jae Won , Do Hyungrok , Kwak Sanghyeok , Han Dongsik , Jung Seungchai , Park Heeho
Published: August 2024

In the aerospace industry, hydrogen has been embraced as a gas turbine fuel. Hydrogen combustion holds significant promise for enabling zero CO2 emissions. However, the transition from hydrocarbon to hydrogen fuel presents new challenges. Designing hydrogen combustors with low NOx emissions across a wide operability range, spanning flashback to lean blowout, requires intensive work, both numerically and experimentally. In this study, a design for an expandable micromixer-type hydrogen combustor is presented. The core design features square fuel rods, each equipped with four orifices for injecting gaseous hydrogen streams, which are rapidly mixed by crossflow to form microflames. Within each fuel rod, a triply periodic minimal surface structure is designed to serve as both a support material and a heat sink for transferring heat from anchored microflames. To achieve a wide operability range, two sets of fuel rods, namely pilot and main burners, are separately controlled with different fuel splits. To maximize the number of flames while preventing flame interaction, these burners were arranged in a staggered grid pattern, with a 45° offset in their orientation. Large eddy simulation (LES) with finite-rate hydrogen-air chemistry was implemented, and the numerical methods were validated by comparing their results with experimental results. The results of LES with the reduced Mevel mechanism were consistent with the test results. The use of additive manufacturing with Ni-based alloy powder significantly reduced the lead times for variant tests, enabling the rapid development and iteration of burner designs. Single-burner tests were conducted under atmospheric conditions, and each configuration was tested with and without confinement using quartz tubes. The presence of an outer recirculation zone improved the resilience of the burner to lean blowout. The LES exhibited good performance in predicting combustion instability under selected conditions. Future works will consider optimizing burner designs and conducting multiburner test under elevated conditions.
Remaining Useful Life Prediction of Aircraft Engine Based on Bi-LSTM Network Integrated With Attention Mechanism
Authors: Qu Guixian , Qiu Tian , Ding Shuiting , Ma Long , Yuan Qiyu , Ma Qinglin , Si Yang
Published: August 2024

Predicting the remaining useful life (RUL) of an aircraft engine is crucial for ensuring the reliability and safety of an aircraft. This study has developed a novel data-driven hybrid network combining a Bidirectional Long Short-Term Memory (BiLSTM) with an attention mechanism to predict the RUL in aircraft engines. The model introduces an innovative approach by incorporating the feature-capture attention mechanism before the BiLSTM layer, which enhances the model’s focus on relevant sensor data segments to enable more effective feature extraction from multi-sensor data. This integration significantly enhances prediction accuracy compared to traditional shallow and deep learning models by leveraging the BiLSTM’s capability to analyze time-series data in both forward and backward directions. The proposed model demonstrates superior accuracy through comparative experiments conducted on the NASA C-MAPSS dataset, underscoring its potential to advance malfunction prediction and health management in aircraft engines.
Experimental and Numerical Study on the Effect of OGV Clocking on ICD Performance
Authors: Jonsson Isak , Capitao Patrao Alexandre , Miltén Petter , Xisto Carlos , Lejon Marcus
Published: August 2024

This paper presents a numerical and experimental investigation into the effects of compressor clocking and stage interaction on the performance of multi-stage axial compressors. The study focuses on the aerodynamic impact of the interaction between the intermediate compressor duct (ICD) and low-pressure compressor (LPC) outlet guide vanes (OGV). Experiments were conducted in Chalmers 2.5 stage low-pressure compressor facility, and numerical simulations were performed using a commercial CFD solver with a Reynolds-averaged Navier-Stokes (RANS) turbulence model. The results show that the clocking position can impact the OGV-ICD performance up to 3% compared to baseline with the dominant effects in the ICD where wake interaction impact transition and the secondary flow structures such as the radial traverse of the hub corner separation. This research provides valuable insights into the role of clocking in ICD design and performance, highlighting its importance as a design parameter. The study is the first to implement IR-thermography for flow visualization in a ICD under engine representative operational conditions.
Numerical Investigation for a Rotating Cavity With Axial Throughflow With Both Axial Heating and Radial Heating
Authors: Zhao Yu , Ding Shuiting , Qiu Tian , Xu Yang , Liu Peng
Published: August 2024

This paper investigates the flow and heat transfer mechanisms of the rotating compressor cavity with axial throughflow under the thermal boundary superimposed by axial and radial heating. In contrast to previous studies, which mainly focused on radial heating, the axial temperature difference increases with the increase of the single-stage compression ratio and is therefore considered in this paper. Verified numerical simulations were used for the study, and the similarities and differences caused by superimposed axial heating were analyzed by comparing situations involving both radial and axial heating, radial heating with a small temperature difference, radial heating with a medium temperature difference, and radial heating with a large temperature difference. The effect of superimposed axial heating on the flow and heat transfer in the cavity was studied under three different Rossby numbers and three different axial temperature differences. The results indicate that the superimposed axial temperature gradient alters the flow field and temperature field in the disk cavity, resulting in different Nusselt numbers for the disk and shroud compared to the case of radial heating only. At low Ro, the buoyancy driven flow is more sensitive to the thermal boundary, so the flow field variation is dominant, and the heat transfer of the high and low radius of the disk varies with different axial temperature differences. At high Ro, the pressure driven flow field is insensitive to the thermal boundary, so the temperature field variation dominates, and the heat transfer of the high and low radius of the disk changes uniformly with different axial temperature differences.
Design and Performance Analysis of a Fuel Cell Propulsion System Driven by a Hydrogen-Fired Micro Gas-Turbine
Authors: Lück Sebastian , Göing Jan , Nachtigal Philipp , Mimic Dajan , Friedrichs Jens
Published: August 2024

A novel design for the cathode air supply system of a fuel cell-based aircraft propulsion system is presented in this study. Herein, the state-of-the-art Electrically driven Cathode air Supply system (ECS) is replaced by a H2-fuelled micro gas turbine (GTCS) with the main goals of 1) decreased total fuel cell power demand and, therefore, 2) reduced low temperature waste heat. Therefore, no parasitic power is required to drive the cathode air supply. The proposed system design is simulated for a regional, distributed propulsion aircraft. Adaptation to other aircraft layouts is easily possible. The operating characteristics of both systems are compared and advantages of the novel architecture are quantified. The advantages are, among others, a substantial reduction of the fuel cell waste heat as well as the reduction of the overall component size within the air supply system. For the most demanding operating point take-off, fuel cell waste heat can be reduced by 25% at maximum operating pressure while heat exchanger size is decreased by up to 16% and humidifier size by up to 20%. Further synergies from the novel architecture are the possibility to use up to 45% of hydrogen from the anode exhaust in the combustor instead of recirculating or venting it. This may lead to a substantial size reduction in the anode side recirculation cycle. Considering the overall system weight, the novel system can achieve a 26% lower weight than the state-of-the-art ECS system. The fuel consumption however is up 9.6% above the ECS system due to poor thermal efficiency of the core. However, it remains to be evaluated in the context of overall aircraft design whether the advantages in component size and weight due to reduced waste heat rejection requirements can outweigh the drawbacks in fuel consumption.
Numerical Prediction of Inlet Geometry Influence on the In-Duct Acoustics of Small Centrifugal Compressors
Authors: Broatch Alberto , Navarro Roberto , García-Tíscar Jorge , Roig Ferran
Published: August 2024

Small centrifugal compressors are employed to boost automotive internal combustion engines or hydrogen fuel cells, amongst other applications. In many scopes, the overall intensity and quality of noise emission is a major concern, so many researchers develop and assess numerical models to predict acoustic spectra. In this work, Detached Eddy Simulations (DES) of a vaneless centrifugal compressor are conducted to assess the impact of intake geometries on its aeroacoustic performance. Experimental measurements are employed as a means of validation. Flow field analysis and Dynamic Mode Decomposition allow us to analyze the underlying mechanisms of the most relevant acoustic features. This work provides insight into the implications for noise generation of employing tight elbows due to packaging constraints.
Analysis of Complex Total Pressure Distortion Screens Using 1-Dimensional Loss Data
Authors: Gillespie John , Hayden Andrew , Lowe Todd , Untaroiu Alexandrina , Nessler Chase
Published: August 2024

Producing a screen for use in generating an accurate, complex total pressure distortion, involves solving two distinct problems. First, the basic loss characteristics of wire mesh screens must be established. Second, the interaction between multiple regions with different loss coefficients (as seen in a complex screen) must be accurately accounted for. Both tasks must be solved effectively to design an accurate screen. For the first goal, we present a comprehensive data set of correlations for the losses generated by a wire mesh, stacked on top of a “backer” support screen. While some publicly available data exists for the losses induced by a single mesh on its own, the losses in a real total pressure loss screen are dependent on the interaction between the backer and the loss meshes. As a result, the data presented here includes the effects of the backer. For the second task, as flow encounters a screen composed of many meshes, it redistributes itself such that the flow rate is higher through the low-loss regions and lower through the high-loss regions. A simple parallel flow model, with appropriate physically-justified assumptions, can accurately predict this redistribution, and we demonstrate its effectiveness via comparison with CFD and experiment.
Influence of Shape and Size of Casting Defects on the LCF Performance of MAR-M247 – A Path Towards a Probabilistic Model
Authors: Radners Jan , Schweizer Christoph , Schlesinger Michael , Eckmann Stefan , Al-Ameri Malek , Amann Christian , Gumbsch Peter , Kadau Kai
Published: August 2024

Addressing anthropogenic climate change is a great challenge that requires integrating renewable energy resources into the grid. The intermittent nature of renewables creates a demand for more flexible gas turbine operation conditions. This increases the number of startup and shutdown cycles and leads to gas turbine components experiencing a significant increase in low cycle fatigue (LCF) loading. This study examines the LCF performance of a widely used rotor blade material to support flexible power plant operation. The study is part of a multi-year government-funded project developing a probabilistic fatigue lifetime model for cast material, including defects like cast porosity. The present work is the second contribution in an ongoing series of studies [1]. The focus of this work is the investigation of the influence of defect size and shape on LCF performance. Because defects introduce a variety of uncertainties, understanding their influence is required for developing a probabilistic approach. Additional model input parameters subject to uncertainties, such as grain sizes and orientations that significantly depend on blade location and design, are also investigated.
Biot Number Error in Low Temperature Inconel Overall Effectiveness Experiments
Authors: Hopkins Bailey W. , Hughes Jacob A. , Bryant Carol E. , Rutledge James L.
Published: August 2024

To predict the performance of turbine materials at engine conditions, experiments are often performed at lower temperature laboratory conditions. In order to ensure the low-temperature, laboratory results accurately predict the nondimensionalized surface temperature at engine conditions, several non-dimensional parameters must be matched in the experiment, including the Biot number. Matching the Biot number requires that the ratio of the thermal conductivity of the material to the thermal conductivity of the air must be matched between laboratory experiments and engine conditions. With traditional nickel alloys such as Inconel, it is sometimes assumed that the Biot number is matched since Inconel’s thermal conductivity variation with temperature scales relatively closely with that of air. However, the thermal conductivity ratio does not scale perfectly and therefore some Biot number error does indeed exist, with the problem exacerbated at lower testing temperatures. To date, there has been no experimentally verified quantification of the error in the overall effectiveness, ϕ, that might be caused by this Biot number error. Based on published thermal conductivity data, Ti-6Al-4V is predicted to allow for a better Biot number match, thereby better simulating Inconel at engine conditions in a typical low temperature experiment. In this research, we utilized geometrically identical models constructed of Ti-6Al-4V and Inconel 718 to evaluate the error in overall effectiveness that might occur through simply using an actual engine nickel alloy part at experimental conditions. While the Ti-6Al-4V model has a nearly perfectly matched Biot number, the Inconel model’s Biot number was 73% higher than appropriate. The overall effectiveness experiments were conducted at a range of advective capacity ratios and the overall effectiveness distributions were compared. The results demonstrate that ϕ measured in low temperature tests performed on an Inconel turbine component do not suffer markedly from Biot number error. The theoretically more Biot number appropriate Ti-6Al-4V model produced area averaged overall effectiveness values that differed by only 0.01 from its Inconel counterpart, within experimental uncertainty, and would only represent a roughly 10 K error in surface temperature prediction at engine conditions. These results suggest that typical nickel superalloys used in turbine components may be tested at low temperature without the use of a surrogate material to better match Biot number.
An Experimental Investigation of the Non-Axisymmetric Casing Treatment for a Low-Speed Axial-Flow Compressor Under Circumferential Inflow Distortion
Authors: Zhao Pan , Zhang Min , Li Yihan , Xu Xiaobin , Ba Dun , Du Juan
Published: August 2024

Aero-engine compressor often suffers from non-axisymmetric total pressure distorted inflow caused by S-duct or BLI inlets. Generally, the distorted inflow can reduce the stall margin (SM) of the compressor. In order to conquer this issue, casing treatment can be adopted for stall margin improvement (SMI). Considering that axisymmetric casing treatment always induces efficiency penalty, this paper conducted an experimental study on non-axisymmetric casing treatment (NACT) for a low-speed single-rotor axial compressor. Two type total pressure distortion inflow conditions including 30° and 60° annular range are involved. Also, various phase differences between NACT and distortion region are investigated. Experimental results indicate a 5.83% and 8.72% decrease in the compressor SM due to the two distorted inflow, respectively. At the near-stall point condition, the self-excited unsteadiness of tip leakage flow gradually intensifies after the rotor rotates into the distortion region, and it has a peak value at the exit of the distortion region where the first spike disturbance occurs. With the change in the phase difference, SMI obtained by NACT initially decreases, then increases, and finally exhibits a slight decrease. The maximum SMI values are 5.61% and 7.86% when the NACT extensively covers the exit of the distortion region for 30° and 60° distortion inflow conditions, respectively. Elaborate test of dynamic pressure and the wavelet analysis demonstrate that NACT can effectively suppress the initial stall disturbance with low-energy at the distortion region’s exit, preventing it from evolving into uncontrollable large-scale and high-energy stall cells. The analysis of the circumferential scale of stall inception indicates that the stall inception will occupy 7–8 blade passages after the application of NACT compared to SC of 2–4 blade passages under distorted inflow, which can provide some insights for future stall warning study.
Dynamical Systems Characterisation and Reduced Order Modelling of Thermoacoustics in a Lean Direct Injection (LDI) Hydrogen Combustor
Authors: Dilip Kumar Ankit , Ezenwajiaku Chinonso , Balachandran Ramanarayanan , Ducci Andrea , Talibi Midhat , Massey James C. , Swaminathan Nedunchezhian
Published: August 2024

Hydrogen is a promising zero-carbon fuel for decarbonised energy and transportation sectors. While carbon emission is not a concern for hydrogen combustion, its higher adiabatic flame temperature poses challenges of mitigating thermal NOx emissions. The wide flammability limits of hydrogen allow a fuel-lean operation, which can reduce NOx emissions. However, lean operation makes the combustion chamber susceptible to thermoacoustic oscillations. In this study, the thermoacoustic instabilities of partially premixed hydrogen flames in a lean direct injection (LDI) multi-cluster combustor are characterised using dynamical systems theory. The combustor was operated at a range of bulk velocities (30–90 m/s) and equivalence ratios (0.2–0.6), and time-resolved pressure oscillations and integrated OH* chemi-luminescence measurements were taken. The thermoacoustic system reveals a variety of dynamical states in pressure such as period-1 Limit Cycle Oscillation (LCO) with a single characteristic frequency, period-2 LCO with two characteristic frequencies, intermittent, quasi-periodic and chaotic states as either bulk velocity or equivalence ratio is varied. At a bulk velocity of 30 m/s, as the equivalence ratio is gradually decreased from 0.6 to 0.2, the dynamical behaviour follows a sequence from an intermittent state to a period-1 LCO, then to a quasi-periodic state, and eventually reaches a chaotic state. As the equivalence ratio is decreased for a bulk velocity of 60 m/s, the pressure oscillations evolve from a period-2 LCO to quasi-periodic state before flame blows off. The emergence of period-2 and quasi-periodic states indicates the presence of strong non-linear interactions among the cavity acoustic modes. These modes and their spatial behaviour are investigated using a reduced order model which solves the 3D inhomogeneous Helmholtz equation with an n-tau flame model. The analyses show that the period-2 and quasi-periodic states can arise due to the interaction between the plenum and combustion chamber modes indicating that hydrogen flames may excite a wide range of cavity acoustic modes.
Dynamic Characteristics of the Tip Clearance Flow Based on the Leakage Flow Model
Authors: Lin Shiyan , Li Ruiyu , Gao Limin
Published: August 2024

Leakage flow in the tip region significantly affects the turbomachinery performance, such as the efficiency, aerodynamic stability and noise. An accurate and in-depth understanding of the dynamic characteristics of leakage flow is the premise of the flow mechanism analysis and flow control. A simplified three-dimensional multi-wall leakage flow model was employed, which characterizes the unique geometric feature of multiple walls with a tip narrow gap and aerodynamic characteristics, i.e., the shear layer between confined jet and mainstream and the tip leakage vortex (TLV). Subsequently, the wall-adapt local eddy-viscosity large-eddy (WALE LES) simulation was used for the simulation. Based on the Liutex and Spectral proper orthogonal decomposition (SPOD) method, the flow structure, main fluctuation structure and unsteady source of the leakage flow were studied. The results shows that there are TLV, secondary tip leakage vortex (STLV) and induced vortex (IV) in the tip field driven only by the leakage flow. The main fluctuation contains the shake of the TLV’s core, breakdown of the IV and generation of the STLV. Furthermore, the STLV has a crucial influence on the development of the vortex structure and unsteady characteristic of the tip field. Kelvin-Helmholtz instability induced by the strong shear layer under the influence of small disturbances is at the bottom of the explosion. However, this cannot be resolved by the Reynolds-averaged Navier-Stokes (RANS) method.
Experimental Investigations on Carbon Segmented Seals With Smooth and Pocketed Pads
Authors: Jolly Pascal , Arghir Mihai , Kasahara Hidetoshi , Kimura Wataru
Published: August 2024

The present paper introduces experimental results for radial segmented seals operating at high rotating speed. These seals are made of three or more interlocking, carbon-graphite segments, in permanent contact with the rotor while also accommodating its dynamic displacements. Currently, many efforts are made to model these behaviors and for obtaining accurate leakage flow rate and friction torque predictions.

A novel test rig fitted with a casing for measuring leakage and friction torque produced by two carbon segmented seals was developed. The tested seals were composed of three segments. Two types of segmented seals were tested: two seals with flat pads and one seal with pocketed pads. The seals were installed two by two in a casing and were simultaneously tested in a back to back arrangement. The process fluid was air, with a maximum inlet pressure of 0.3MPa, while it was set to ambient at the outlet. The rotor diameter was 100mm with a maximum rotating speed of 24,000rpm. The main measurements were the inlet mass flowrate and friction torque produced by the two seals.

Results show that the seal with pocketed pads produced higher leakage rates but lower friction torque compared to the smooth pads. This suggests that the seal with pocketed pads operated with segments completely lifted from the rotor surface. Mass flow rates measurements during run-up/coast-down tests allowed to highlight a hysteresis effect, which could be the consequence segment tilt. The experimental results could also be useful to validate theoretical models.
Relationship Between Wavy Liquid Film Dynamics and Droplet Formation From Trailing Edge
Authors: Kamada Yoshiaki , Murakami Keito , Wang Zhenying , Inoue Chihiro , Senoo Shigeki
Published: August 2024

Erosion of steam turbine blades due to coarse droplet impingement is a serious problem. The physical relationship is still elusive between the dynamics of wavy liquid film on a wall and the droplet dispersion from the trailing edge. In this study, we experimentally and theoretically investigate the liquid film subjected to the turbulent airflow and following fragmentation process under well-controlled flow conditions, where the airflow velocity is up to 100 m/s, and initial liquid film velocity is 0.06 and 0.10 m/s, and trailing edge thicknesses are 0.5, 1.0, and 2.0 mm. By applying the developed PLIF based method with no use of artificial threshold of brightness, we quantify the film thickness and interfacial friction factor. As the airflow velocity increases, the liquid film instability promotes and the interfacial friction factor increases, much exceeding the Blasius correlation. When the liquid film reaches the trailing edge, several liquid columns extend by the Rayleigh-Taylor instability. We identify that the interfacial friction factor to accelerate the ligament corresponds to the Blasius correlation, distinct from the one on the wavy liquid film upstream. Incorporating the identified two interfacial friction factors, we successfully formulate the diameter of ligament as the characteristic lengthscale of the spreading droplet downstream. Derived formulation for the droplet statistics is well validated by the experimental results of mean and maximum diameters and size distribution.
Comparative Analysis of Total Pressure Measurement Techniques in Rotating Detonation Combustors
Authors: Wei Hongyi , Kayser Tim , Bach Eric , Paschereit Christian Oliver , Bohon Myles D.
Published: August 2024

Current total pressure measurement techniques in RDCs are based on different assumptions and therefore show different applicability for specific RDC operating conditions, and few studies have directly compared these techniques. Therefore, this study comprehensively tested three total pressure measurement techniques: the direct Kiel probe method, the Mach-corrected CTAP method, and the equivalent available pressure (EAP) method under different RDC geometries and mass flow rates, and compared them with their corresponding uncertainties considered. The results show that for all tests in this study, the EAP method shows the largest uncertainty range up to 24%, which is mainly contributed by the load cell calibration process, while the direct Kiel probe method has the lowest uncertainty range, which is consistently below 7%. These uncertainties were incorporated into the comparison between the three techniques via Gaussian process regression, showing that the direct Kiel probe method and the Mach-corrected CTAP method can present EAP-like total pressure. In particular, the total pressure of the SWCC and L modes measured by the three techniques is very comparable. This work shows that the comparability of total pressure techniques depends on the specific RDC environment, and provides the possibility to evaluate the RDC performance with the simplest implementation.
The Onset of Hydrodynamic Instability in Dual Orifice Atomizers
Authors: Kılıçgedik Hıdır Yankı
Published: August 2024

This paper deals with the numerical investigation of inner flow instability in pressure swirl atomizer with a “nozzle within a nozzle” configuration. It begins with an overview of the high fidelity hybrid RANS-LES approach for interface capturing of turbulent multiphase breakdown process. This was followed by a brief discussion on the underlying physical mechanism of the unstable mixing and the transition of this action to Kelvin Helmholtz waves. Three new practical guidelines for instability evaluation were brought to the attention of the readers; flux-based estimation for the time variation of cone angle, sheet deformation ratio and a mathematical analysis of stability based on the standard deviation of the time fluctuating flow characteristics.

The combination of these complementary methods can be used to accurately identify the onset of flow instability. Derived from simple theoretical foundations, these methods have the potential to provide practical benefits for the performance assessment of different injector configurations in industrial applications.
A Physics-Informed Neural Network Surrogate Model for Mistuned Bladed Disks Dynamics
Authors: Fan Yu , Fan Jiasen , Li Anlue , Wu Yaguang , Zhang Yuning , Song Zhiqiang
Published: August 2024

Background: The inevitable mistuning of a bladed disk breaks the cyclic symmetry of the structure and can cause vibration localization and amplitude magnification, thereby seriously reducing the structural reliability. Although numerical simulations based on high-fidelity finite element models can precisely calculate the response under some specific mistuning patterns, repeated calculations of random mistuning cases still bring a significant computational burden, even with ad-hoc reduced-order modeling technologies.

Objective: In this work, we aim to capture the dynamics of randomly mistuned bladed disks using data-driven surrogate models.

Methods: To do that, a physics-informed surrogate model of a designed structural neural network (DS) is proposed, where a “shift” feature from the cyclic symmetry in physics is taken into account for data augmentation. The finite element model of a dummy bladed disk with blade stiffness mistuning is established and taken as an example to test the effectiveness of the surrogate model. Under different training set sizes and excited modes, the performance of the proposed model is compared systematically with a fully connected structural neural network model (FC) and a state-of-the-art deep neural network framework (MS-DNN).

Results: The DS model can accurately predict blade displacement for blade-dominated modes with only 600 training data. The R2 value of the displacement response amplitude reaches 0.99956, and the error of the amplitude magnification factor is only 0.68%. The DS model converges faster and has higher prediction accuracy than the FC model. The DS model is superior to the MS-DNN model concerning the generalization ability.
Study on the Impingement Cooling Structure With the Characteristic of Low Flow Resistance
Authors: Li Changwei , Guo Tao , Liu Cunliang , Zhu Huiren , Li Guodong , Wang Xinyu , Li Jiayu , Liu Shanjie
Published: August 2024

As an efficient cooling method, the impingement cooling in the mid-chord of the aero-engine turbine vane causes the jet to impact the target plate, resulting in a thin boundary layer near the stagnation point and high heat transfer, which other aeroengine internal cooling technologies cannot achieve. Adding pin fins to the target plate is a standard method to improve impingement cooling, but it reduces the coolant flow area in the impingement chamber to increase the flow resistance. This paper proposes a novel structure with low resistance characteristics by adding V-ribs to the target plate. The novel structures’ flow and heat transfer characteristics are studied through numerical simulations and experiments. The Reynolds Averaged Naiver-Stokes (RANS) model is adopted for the 3-D steady-state numerical simulation, and the shear stress transport (SST) k-ω turbulence model is used for closing the governing equations. The main conclusions are that the jet Reynolds number (Rej) and the flow-pitch of the impingement hole are critical factors that affect heat transfer, and the change in the jet-to-plate distance can significantly influence flow resistance. As the jet Reynolds number increases from 2000 to 15000, the average Nusselt number on the impingement target surface increases by a factor of 3.6. The flow coefficient at an impingement distance of 3 is 1.45 times that at an impingement distance of 1. The increase in the jet Reynolds number and the reduction in the flow-pitch of the impingement hole enhance the heat transfer on the target plate by increasing the impingement and wall jet velocities respectively, thereby enhancing the scouring effect. The decrease in pressure in the intake chamber and the corresponding decrease in the pressure gradient in the impingement chamber are the main reasons for the decrease in flow resistance caused by the enlargement of the jet-to-plate distance.
Experimental and Numerical Investigation of Heat Transfer in a Turbocharger Turbine in Consideration of a Diabatic Heat Shield
Authors: Gier Thomas-Sebastian , Luczynski Piotr , Wirsum Manfred
Published: August 2024

Thermal loads play a major role in determining a turbocharger turbine’s lifecycle. The turbine wheel in particular is subject to varying thermal loads, which induce inhomogeneous temperature distributions causing thermo-mechanical stress. In order to calculate these thermal loads the mechanisms governing the heat transfer inside a turbocharger turbine have to be known as precisely as possible. One of these mechanisms is heat transfer from the wheel backside through the heat shield into the bearing housing, which is commonly neglected. This paper aims to fill that gap by exploring the effect of heat transfer through the heat shield of a turbocharger using both experimental and numerical data.

As part of this investigation a brief summary of the experiments with an instrumented turbocharger is presented. These experiments subjected the turbine to several stationary load conditions ranging from minimum to maximum operating points for multiple rotational speeds. Hereby, temperatures in the stationary and rotating parts of the turbine were recorded.

Due to the complexity of the temperature field inside the turbine, experimental data alone does not offer a sufficiently detailed account of the occurring processes, because it is only recorded at discrete points. Therefore, a numerical model is presented, which encompasses both fluid and solid parts of the turbine to enable CHT simulations to be conducted. These simulations allow for a more complete analysis of the heat transfer between turbine wheel and bearing housing due to the availability of data at all locations. To verify the correctness of the numerical results the model is first validated using the experimental data and shown to be a good match. It is then used to analyze heat transfer mechanisms between the backside of the turbine wheel, heat shield and bearing housing, as well as their impact on the temperature field of the turbine wheel.