bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantification of Mixing Quality Effects on Flashback Limits for H2-Rich Fuel Gases
Authors: Kim Taesung , Doll Ulrich , Faldella Filippo , Jansohn Peter
Published: September 2023

One of the main challenges arising from hydrogen-rich fuel mixtures is to prevent flame flashback. In typical gas turbines the fuel is commonly injected through holes in the axial swirler vanes to achieve a high mixing quality. However, this injection method is not perfect and can cause non-homogeneous mixing regions, so that locally rich fuel clusters can significantly increase flashback propensity. This work aims to establish a link between the local mixing quality of fuel and air and flashback limits obtained experimentally under elevated pressure conditions. The non-reacting experiments have been conducted at an atmospheric mock-up test rig and acetone-PLIF has quantified the local fuel concentration. Zones of high equivalence ratio are evident close to the center body wall. The near-wall equivalence ratio fields reveals that the critical probability of the local equivalence ratio being greater than the one for perfect premixing is between 20% and 35% for all hydrogen concentrations at the flashback limits observed. A probability of 35% is selected as a critical threshold to derive a correlation between the local and the global equivalence ratio in technical premixing. Even though the correlation is specific to the investigated burner configuration, the presented methodology offers valuable insights into the impact of the local mixing quality on flashback propensity, which can improve flashback prediction models formulated for perfect premixing conditions.
Evaluating the Effect of Liquid Water and Steam on Jet Flame Physics
Authors: Schihl John , Skiba Aaron W. , Carter Campbell D. , Gandomkar Amirreza , Whitcomb Jack , Allison Patton M.
Published: September 2023

The present research effort focuses on determining the effect of steam and liquid water addition on flame structure in preheated, premixed, piloted methane-air jet flames. The turbulent Reynolds Number (ReT) varied between 760 and 4,200, and two equivalence ratios (0.9 and 1.1) were considered. Planar laser-induced fluorescence (PLIF) imaging of OH radicals was performed via excitation of transitions in its A-X (0,0) band (near 311 nm). Flame surface density (FSD) and average progress variable maps (c−) were derived from those images, which facilitated analysis of the turbulent flame-surface area ratio, brush thickness, and turbulent flame speeds. It was found that steam had a large impact on flame surface statistics, whereas liquid water with similar mass fractions had little-to-no effect. In cases with varying steam loading but the same ReT, FSD along the mean reaction variable contours did not appear to be affected, and minimal changes in flame structure were observed. A weak correlation between brush thickness and steam flow rate was observed, whereas liquid water addition had no impact on brush thickness. In addition to the experimental aspect of this study, computations were performed using CHEMKIN to investigate the effect of steam loading on freely propagating premixed methane-air flames. Laminar flame speed decreased with increasing steam and argon concentration, with results suggesting the leading order impact of steam dilution is to act as a heatsink due to its large specific heat constant.
Adaptation of Aeroengine Micromixing Injectors for Lean Direct Injection of Hydrogen and Hydrogen/Natural Gas Blends
Authors: Gomez Escudero Iker , Tran Britney , Overbaugh Malcolm , McDonell Vincent , Williams Brandon , Buelow Philip , Ryon Jason , DeBeni Ottavio
Published: September 2023

A set of novel fuel injectors has been developed and manufactured for systematic evaluation of the combustion performance of hydrogen and hydrogen/natural gas mixtures. The test hardware is derived from lean direct injection concepts developed for low emissions aeroengines. Computational Fluid Dynamics (CFD) was used to design the test hardware using target flows associated with a Solar Turbines industrial engine. A statistically designed test plan was adopted to study the effect of air split, air swirl, and fuel swirl on the combustion performance. A Box-Behnken three level design was used to facilitate the development of response surfaces of performance as a function of the design factors considered. This resulted in a total of 13 test configurations. Three additional configurations were also developed to allow validation of response surface correlations. Atmospheric combustion testing was carried out for a range of preheats, injector pressure drops, and fuel type. Prior to the combustion tests, air flow testing was performed on each injector to quantify the effective areas of the fuel and air circuits. The air effective area was consistent within 2.5% for the 16 test parts. The fuel side effective areas varied by about 12%. Considering the parts were all additively manufactured, the variation was considered reasonable. Next, an atmospheric combustion testing was performed to study the lean blowoff characteristics and flame stability, and it was determined that the air splits and air swirl were more statistically significant than the fuel swirl. While all configurations were stable, the configurations with lower air swirl had increased stability. Lower air pressure drop across the injector and increased preheat temperatures increased the stability range, and also allowed increased hydrogen content. Finally, the mid-point injector design was further studied with atmospheric combustion including emission sampling and imaging, and a set of these results are included herein. This expanded effort defined a baseline which allows the comparison of the full matrix of injectors that is going to be studied in subsequent efforts, to characterize the performance of each individual injector design at atmospheric conditions.
Accelerated Structural Assessment for Risk Reduction of an AM Cruciform Rotor
Authors: Scott-Emuakpor Onome , Warner Justin , Celli Dino , George Tommy
Published: September 2023

Minimal material information is used to accelerate the structural assessment of an additive manufacturing (AM) fabricated stainless steel 316L cruciform rotor in a spin rig environment. The primary purpose of the spin test is to demonstrate the vibration suppression and damage tolerance capability of the Inherent Damping via AM Processes (i-DAMP™) technology. Therefore, the rotor is expected to experience induced vibration fatigue as well as centrifugal load stresses, which make the rotor susceptible to Burst and High Cycle Fatigue (HCF) failures. All the material data necessary to determine limits for Burst and HCF are acquired from 12 coupon specimens built during the same Laser Powder Bed Fusion (LPBF) print operation as the rotor. Using tensile strength, fatigue, and computed tomography scan data from both coupon specimens and the rotor, this study establishes a safe approach using minimal data to set the structural limits of a critical AM component operating in an extreme environment.
Numerical Simulation of an Organic-Rankine-Cycle Nozzle Cascade Using a Tabulated Real-Gas Thermodynamics Model for Siloxane MDM
Authors: Haake Alexander , Wittek Matthäus , Müller Hagen
Published: September 2023

Power generation based on the Organic Rankine Cycle has become a viable option for exploiting the large potential of thermal energy currently emitted into the environment as waste heat in many industrial processes. For this reason, reliable and efficient numerical methods are needed to improve current designs and increase their efficiency. In this work, a pressure-based CFD solver is used to perform Reynolds-averaged Navier-Stokes simulations that extract the real-gas thermodynamic properties from look-up tables. The tables are generated using a recent multi-parameter equation of state based on the Helmholtz residual energy. The method is applied to simulate two configurations using the working fluid octamethyldisiloxane (MDM). As a first step, the numerical method is validated for a converging-diverging nozzle flow under non-ideal operating conditions. The simulation results agree well with available measurements for pressure and Mach number on the centerline. The method is then used to simulate a linear blade cascade operating in the non-ideal supersonic regime. The results are analyzed in terms of properties along the blade surface and the expansion-shock system starting at the trailing edge. Good agreement with other simulation results is obtained. A runtime analysis shows that tabulating thermodynamic properties significantly reduces the numerical effort. In summary, these results demonstrate the suitability of this approach for simulating non-ideal compressible fluid flow applications.
Integration of a Gas Model Into CFD Analysis for the Simulation of Turbine Exhaust Flows With High Steam Loads
Authors: El-Soueidan Mahmoud , Schmelcher Marc , Görtz Alexander , Häßy Jannik , Bröcker Marius
Published: September 2023

The Water-Enhanced Turbofan (WET) is a promising future propulsion concept to reduce aero engine emissions. In the WET-engine, a heat exchanger uses turbine exhaust heat in order to generate superheated steam out of liquid water. For evaporator design, CFD simulations are necessary since correlation-based predictions have a high uncertainty during preliminary design. A common way of modeling steam loaded flows is the integration of gas models into CFD analysis. However, to the author’s knowledge, there is no gas model published that accounts for the exact gas composition of turbine exhaust flows with high steam loads and is commonly used by low- and high-fidelity methods. Therefore, a gas model predicting the thermodynamic behavior of the turbine exhaust flow considering high steam loads is presented and integrated into an existing CFD solver. The approach is able to incorporate the implemented gas model into the CFD simulation by two methods: runtime and offline. The offline method has a computational advantage in iteration time compared to the runtime integration. As demonstration case, a single two dimensional cylinder is considered. A variation of the steam loading of the flow shows a significant effect on local properties and therefore on local and average heat transfer. Increasing the steam loading up to 40% results in an increase of the average Nusselt number of 17%.
Gas Turbines Cantilever Nozzles Simplified Approach for Performance and Structural Optimization
Authors: Fardelli Andrea , Ragni Giacomo , Di Benedetto Daniele , De Luca Alessandro , Colantoni Simone
Published: September 2023

One of the most critical phases of designing a competitive product such as a Gas Turbine is the conceptual phase, in particular the definition of the flow path, which decides the performance of the engine. Therefore, the ability to optimize the aerodynamic performance of the flow path has significant benefits, but, due to constraints related to the reduction of the time to market of new products, the optimization process is extremely limited.

Typically, the definition of an acceptable flow path is an iterative process between the Aerodynamic and Structural teams, which requires a considerable amount of time leaving very little space for optimization.

Considering the common architecture of a turbine, only the first stage nozzle can be supported both at inner and outer diameter, while all the other stages can be only supported at the outer. This leads to an extraordinarily strong structural and life constraint for airfoils definition because they must be properly seized to comply with creep requirements.

According to the earlier design process, the aerodynamic optimization of the flow path was performed by means of a 1D tool, later on airfoils were built and analyzed from a structural standpoint to verify if they were complaint.

The proposed function is based on a newly developed transfer function between the geometry parameters available from the 1D aero tool and the bending stress on the airfoils. Function has been trained on legacy engines and later verified and applied in ongoing studies.

In this way the aerodynamic optimizer can obtain a preliminary mechanical assessment in real time on each configuration of the 1D flow path, allowing to generate only structurally verified configurations.

The article explains how the tool works along with a case study highlighting its application. The findings confirm that this innovative tool can simplify and speed up the optimization of a 1D flow path.
Axial Compressor Loss Sensitivity Analysis to Blade Row Design Parameters
Authors: Cruz Gonçalo G. , Babin Cedric , Fontaneto Fabrizio
Published: September 2023

In the preliminary design phase of an axial compressor stage, the selection of the most relevant design parameters within the shortest amount of time is paramount. An easier convergence toward the final design limits the use of costly optimization loops and extensive computational fluid dynamics simulations. By coupling a previously published physics-based loss decomposition tool, a mean line analysis, and radial equilibrium codes, the current study investigates the influence of design variables on blade row total pressure loss contributions. The core of the work presents a strategy to exploit the state-of-the-art design space. The compressor stage loss sensitivity to the design variables selected is evaluated using the probabilistic method of Sobol indices, quantifying parameters non-linear interactions inherent to the design process. As an example, the study synthesizes the relationship between loading, solidity, and row inlet boundary layer displacement thickness, to profile loss, end wall loss, and tip leakage loss. As a result, this work ranks the relative influence of the selected design parameters in the different loss sources, a process that may not be obvious from a term-to-term analysis of the loss models used.
Analysis of Single Blade Passage and Full Circumference Large-Eddy Simulations of Turbine Rim Seal Flows
Authors: Hösgen Thomas , Meinke Matthias , Schröder Wolfgang
Published: September 2023

The flow in a 1.5-stage axial flow turbine with 16 vanes and 32 blades is investigated by large-eddy simulations with special focus on the analysis of the hot gas ingress through the rim seal into the upstream wheel space. Two setups with different solution domains are used. In the first large-eddy simulation, the full circumference of the turbine is resolved on a mesh with approx. 1 billion mesh cells. The second setup includes only a single blade passage and is solved on a mesh with approx. 75 million cells. The analysis shows that the flow fields inside the upstream wheel space, i.e., between the disk of the upstream stator and the rotor disk strongly differ. In the 360° domain two large-scale rotating vortex structures are observed, which have a strong impact on the ingress of main annulus gas into the wheel space. These structures cannot be captured in the single blade passage domain. The instantaneous flow fields are further analyzed by Dynamic Mode Decomposition to determine similarities and differences in the two flow fields. The comparison of the modes from the two setups reveal that the hot gas ingress from modes at the blade passing frequency generate a reduced sealing efficiency only at the outer radius of the wheel space. The additional presence of large-scale modes, however, reduce the sealing efficiency also in the inner wheel space. These results suggest that a single blade passage simulation cannot be used for a reliable prediction of the hot gas ingress for the investigated turbine setup and operating condition.
Prediction of Gas Turbine Trip by Combining Gas Path Measurements and Vibration Signals
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Bechini Giovanni
Published: September 2023

As well-known, gas turbine (GT) trip causes a reduction of GT lifespan and makes costs increase, because of unscheduled stops. Thus, predicting GT trip in advance would allow saving costs and maintaining high operational efficiency and availability.

For these reasons, this paper presents the development of a model based on deep learning, i.e., a temporal convolutional neural network, aimed at GT trip prediction. The model exploits both vibration data collected from multiple sensors installed at different locations of the GT asset and gas path measurements. Its prediction capability is compared to that of the models fed only with vibration signals or gas path measurements. The simultaneous exploitation of vibration signals and gas path measurements, which is the main novel contribution of this paper, is aimed at enhancing the reliability of GT trip prediction, since trip causes are heterogeneous.

The paper also investigates different time frames for predicting GT trip, by considering training and testing time windows taken at different time points from trip occurrence.

The case study is represented by a collection of field measurements referring to real-world GT trips taken from multiple GTs during several years of operation. The field data used to validate the results cover multiple ambient and operating conditions.

The results demonstrate that the simultaneous exploitation of both gas path measurements and vibration signals actually enhances the reliability of GT trip prediction in the majority of the considered cases, with accuracy values up to 73%.
Experimental Nonlinear Analysis of Pre-Loaded Turbine Blades Dynamics With Frictional Shroud Contact
Authors: de Filippis Hugo , Thouverez Fabrice , Blanc Laurent , Girard Patrick , Chevillot Fabrice
Published: September 2023

The evaluation of damping, obtained as a consequence of the frictional contact between shrouded blades of a low-pressure turbine, is of major interest in the aeronautical industry. The main purpose of the shrouds is to keep the tightness of the primary air stream, but it also produces a nonlinear damping which makes it possible to limit the blades vibration amplitude during classical service conditions of a plane turbojet, like take-off or cruise. One of the possible technological choices to introduce this nonlinear damping consist of having a geometrical design of the low-pressure turbine blades which includes a pre-torsion angle, and will produce a static loading of the blades after the assembly, when the shrouds are brought into contact. In dynamic conditions, the contact between the shrouds can evolve to different statuses like bonding, sliding or even separation, which obviously leads to a strongly nonlinear behavior and depends on certain parameters like levels of excitation force, friction coefficient and static loading.

In order to reproduce as accurately as possible the static loading of the blades due to the pre-torsion angle, an experimental test bench has been designed and manufactured. The main goal is to evaluate the nonlinear damping through dynamic responses. The materials used and the manufacturing process are mentioned. The major novelties of the proposed test bench in comparison to the ones found in the literature are firstly the presence of three test blades, secondly the application of a static loading thanks to the blades assembly with the pre-torsion angle, and thirdly the realistic Z-shape shroud geometry.

Several experimental results are presented in this article: some modal analyses of the blades in free and embedded conditions to validate the numerical model and to estimate the blades disparity. Then each blade has been calibrated by means of strain gauges to estimate the applied torsion torque, to control precisely the blades position and the repeatability of the assembly process. Finally, the blades are tested under a dynamic excitation, using an electro-dynamic shaker and a laser Doppler vibrometer. The aim of this experiment is to observe the nonlinear damping on the blades frequency responses, and its dependence to different varying parameters like the excitation force, the static loading, etc.
Suppressing Energy Localizations in Rotating Machinery With Realistic Noise
Authors: DeBoer Jonathan , Breunung Thomas , Balachandran Balakumar
Published: September 2023

Vibrations in rotary machinery can increase wear, leading to a decreased lifetime. Especially harmful are localized vibrations, during which only a small region of the machine vibrates significantly. Apart from imperfections and non-homogeneities, such energy localizations can be induced by the structural nonlinearities of turbine blades. Through previous experiments and simulations conducted in the authors’ group, it has been shown that Gaussian white noise can effectively suppress these energy localizations. However, the Gaussian white noise model is unphysical, since the associated energy is infinite. Thus, the efficacy of suppressing localization with more realistic noise in rotating machinery remains to be studied.

Motivated by the beneficial employment of noise, the authors explore the utilization of omnipresent noise in turbomachinery applications as a low-cost control strategy to destroy undesired energy localizations. To this end, the authors present an experimental study to investigate the impact of different noise sources on the suppression of localization in rotating machinery applications. Building on prior efforts in the authors’ group, the authors utilize a test-rig consisting of a circular array of cantilever beams, which are representative of machinery blades, and magnets that are used to induce nonlinear restoring forces. Due to these nonlinearities, the system has multiple stable vibrational states and localized high-energy vibrations. The influence of different noise sources on such localized response states is investigated.
The Effect of Ignition Procedure on Flashback of Hydrogen-Enriched Flames
Authors: Yahou Tarik , Schuller Thierry , Dawson James R.
Published: September 2023

The impact of different ignition sequences on the ignition dynamics of CH4-H2 flames in a bluff body burner is investigated at atmospheric conditions. Experiments are performed over a wide range of operating conditions covering pure methane injection (PH0) to pure hydrogen injection (PH100). A perforated plate of total porosity σ = 0.17 is positioned at the outlet of the combustion chamber to increase the chamber back pressure and trigger transient flashback during ignition. Time-series of pressure, OH* chemiluminescence and OH-PLIF images of the propagating flame branch are recorded simultaneously to characterize the ignition process. Two ignition procedures are investigated. For ignition procedure A, designated as an early ignition procedure, the spark is initiated before fuel injection. For ignition procedure B, designated as a late ignition, the spark is only activated after the fuel injection. The impact of the fuel air mixing on the final stabilization state is investigated by changing the fuel delivery time (dt) before the initial spark. Three different time delays are considered dt = 1, 3 and 5 s. The final state of the flame is found to be highly sensitive to the selected ignition procedure and increasing dt favors the occurrence of flashback. At constant power, the magnitude of the pressure peak is driven by a competition between the fuel mass flow rate at the moment of ignition and the high reactivity of hydrogen which shifts the flammability limit towards lower equivalence ratios, hence generating a lower reaction rate. For procedure A, the peak of the chamber over pressure shows a non-monotonic growth for increasing levels of H2 in the fuel blend, while it linearly increases for procedure B. Experiments are then conducted at a fixed injection flow velocity Ub = 5 m.s−1 and fixed laminar burning velocity Sl0 = 0.25 m.s−1 by varying the level of hydrogen enrichment. For procedure A, the over pressure amplitude decreases with increasing the hydrogen enrichment leading to a soft ignition for all CH4-H2 blends. Under ignition procedure B, the amplitude of the over pressure reached during ignition is found to be relatively unaffected by the hydrogen concentration, but the flame stabilization mode shows a strong dependence to both the level of H2-enrichment and fuel delivery time dt. OH* as well as OH-PLIF images reveal that the trajectory of the flame leading point changes as dt increases. The different dynamics of the flame leading points is likely to be the cause the different types of stabilization modes observed.
Analytical, Numerical and Experimental Study of Flutter in a Realistic Labyrinth Seal
Authors: Bermejo Oscar , Gallardo Juan Manuel , Sotillo Adrian , Altuna Arnau , Alonso Roberto , Puente Andoni
Published: September 2023

Labyrinth seals are frequently used in modern turbomachinery in order to control leakage flows between static and rotating elements. Previous experiences have demonstrated that flutter is a potential risk for them and can lead to high cycle fatigue life reduction or even mechanical failure. This aeroelastic instability depends on the interaction between aerodynamics and structural dynamics and it is hard to predict accurately due to its sensitivity to the details during operation. In 2014, as part of the E-Break European Union research project, an experimental campaign aiming to study the phenomenon was conducted at Centro de Tecnologías Aeronáuticas. Three realistic seal geometries were tested at a comprehensive set of operating conditions and all of them exhibited flutter at some point. These seals will be the object of study of this work. This document is a continuation of a previous publication of the authors where the E-Break campaign was reproduced with a methodology based on Computational Fluid Dynamics simulations. The simulations showed a good agreement with experimental data and revealed the importance of accurately predicting the actual fin gaps during operation and the influence of external cavities. Here a new approach to study the stability of the seals is followed, consisting in the use of a simplified analytical model based on the works by Corral, Vega and Greco. The model is the result of solving a linearized version of the governing fluid equations under certain simplifying hypothesis. The stability results obtained are compared against both the available experimental data and the aforementioned high-fidelity simulations, showing a fairly good agreement at a vastly reduced computational cost. However, the main limitation of the model arises in those cases where the stability is dominated by the external cavities, as the simplified model is not able to account for their effect.
Coherent Turbulent Stresses in Unsteady Forced Transonic Nozzle With Shock-Induced Separation
Authors: Goffart Nicolas , Tartinville Benoît , Pirozzoli Sergio
Published: September 2023

The influence of rotor/stator interference on shockwave/boundary layer interaction is investigated by means of an implicit large-eddy simulation. To replicate actual turbomachinery conditions but at a lower cost, this work considers a transonic bump over which a shock-wave develops and interacts with the separated boundary layer. Moreover, the backpressure is set to fluctuate at a realistic reduced frequency. The analysis is focused on the coherent component of the flow and more particularly the turbulent stresses in the recirculation region. Phase-averaging is performed in order to highlight this component and the reference oscillator is based on the location of the separation point. Statistical convergence is assessed. Coherent turbulent stresses show a two-layers pattern, the upper layer being linked to the mixing layer and the inner layer developing below. The coherent component can reach up to 60% of the local mean value. Budgets show that only some production terms are significant and each of them is acting upon a specific layer of the associated coherent turbulent stress. Finally, pressure strain, responsible for the coupling between the transport equations, is also of importance.
A System Dynamics Approach to Assess the Impact of Policy Interventions on the Market Penetration of Micro Gas Turbines
Authors: Sharma Kirti , Al-Zaili Jafar , Sayma Abdulnaser
Published: September 2023

Decentralized power generating systems, such as micro-gas turbines (MGT) for micro combined heat and power (CHP), can contribute to achieving the global energy and emission targets thanks to features like low emissions, primary energy savings, and fuel flexibility. It can also help increase the share of renewables due to its ability to easily integrate with renewable energy systems. Micro gas turbines, despite being such a promising technology, have achieved very limited market success due to barriers like high investment costs and a lack of supporting policies. The large-scale market penetration of MGT requires clear and strong policy support to achieve widespread adoption.

This paper establishes a quantitative model to assess the impact of the policy measures on the long-term market penetration of MGT for the domestic micro-CHP to establish a relationship between policy parameters, economic factors, technological advancements, and the market share of MGT.

The work compares five different policy scenarios for the case study of the UK market. The results demonstrate that the usual economic forces are insufficient for MGT to achieve its long-term market growth. Several combinations of direct and indirect policies are to be implemented by the regulatory authorities to promote the commercial growth of the technology. Finally, some insight into policy and decision-making in the UK for micro-CHP is provided, indicating promising policies to pursue.
Efficient Pressure Mapping for the Calculation of the Dynamic Force on Reduced Order Models of Bladed Disks
Authors: Bouras Abdelhakim , Carassale Luigi
Published: September 2023

The design of bladed disks involves both fluid dynamic and structural calculations through numerical methods that involve the discretization of the domains. On the fluid side, computational fluid dynamics (CFD) software is used while on the structural side, models are formulated by the finite element (FE) method and are reduced using different model reduction techniques.

The fluid and the structural model are coupled as the aerodynamic pressure induces a load on the blades, while the blade deformation changes the boundary conditions for the flow field. In industrial applications, this fluid-structure interaction problem is usually implemented only partially, adopting a oneway coupling.

In forced-response calculation, the aerodynamic pressure is calculated using the geometry obtained, including the static blade deformation (mean pressure load, centrifugal force, temperature), disregarding the dynamic part of the response. The dynamic pressure field calculated in this way is then used as a dynamic load for the structural model. On the other hand, in flutter analyses, the blade motion is prescribed according to a selected mode shape, frequency and inter-blade phase angle and is used to define the boundary conditions for the CFD model. In both situations, it is necessary to transfer information (pressures or displacements) between the fluid and the structural model.

This paper describes a technique to transfer the pressure field calculated by a CFD analysis to a structural Reduced-Order Model (ROM) obtained from a high-fidelity FE model of the disk. The generalized forces acting on the ROM are obtained as a linear mapping of the pressure computed on the boundary of the CFD domain. This mapping depends only on geometry and mesh topologies, thus it can be calculated only once in a structural analysis, while for each time or frequency step, the generalized forces are obtained through a matrix multiplication.
Experimental and Numerical Investigations of Grain Size Changes in the Rim Zone During Turning of DA718
Authors: Gerhard Nicklas , Liu Hui , Splettstößer Antonia , Massanés Pedró Pere , Meurer Markus , Bergs Thomas
Published: September 2023

Safety critical engine components, whose functionality and longevity demands a high surface integrity, are widely made of the direct aged nickel-based alloy DA718. The high strength and low thermal conductivity of DA718 lead to high thermal loads, which causes modifications of the microstructure in the rim zone. Changes in grain size can result in cracking and thus detrimentally affect component functionality. According to the current state of the art, numerical simulation methods can be used to model the machining induced rim zone modification. For this purpose, experimental investigations of orthogonal cutting and friction tests were performed to determine the viscoplastic properties of the DA718 and frictional behavior between workpiece and tool. Based on this, a turning simulation was developed using the Coupled Eulerian-Lagrangian (CEL) method. This is followed by the implementation of a numerical model for the prediction of grain size changes in the workpiece rim zone. To validate this model, face turning tests of DA718 was performed with a ceramic tool, and the grain size alterations were compared with the simulation. The Comparison showed, that the model agreed well with the experimental measurements for different cutting conditions.
Mistuning and Damping of a Radial Turbine Wheel. Part 3: Validation of Intentional Mistuning During Machine Operation
Authors: Nakos Alex , Beirow Bernd , Wirsum Manfred , Schafferus Markus , Sasakaros Marios , Vogt Damian , Zobel Arthur
Published: September 2023

This contribution investigates the implementation and verification of intentional mistuning (IM) to a radial turbine wheel of an exhaust turbocharger. In principle, inaccuracies in manufacture or material inhomogeneities may lead to random blade mistuning and thus localized modes with severely magnified blade vibrations can occur. With regard to axial compressors and turbines, IM has proved to be an efficient measure to mitigate the forced response. For radial turbine wheels, on the other hand, a successful implementation of IM into a wheel hardware has not yet been presented. This work aims at the design, implementation, and verification of successful IM considering both measurements at standstill and test runs on a turbocharger test rig.

The fundamental analyses have been carried out in part one [1] of this three-part paper in order to find a suitable IM-pattern featuring only two different blade designs. The AABB sequence was identified to be the most promising one in terms of mitigating the maximum forced response of the fundamental bending mode at the considered operating point. In concrete terms, a 40% attenuation of the maximum forced response was predicted by employing reduced order models.

The second part [2] discussed the detailed geometric adaption of the turbine wheel hardware focussing on the implementation and validation of the IM pattern under laboratory conditions (standstill). Part three is about validating the efficacy of IM under operating conditions. In that sense, the successful implementation of IM and thus the machining of the wheel hardware are investigated within the framework of test runs on a turbocharger test rig. Test runs are conducted for both a wheel with and a wheel without IM. Non-intrusive blade-tip-timing (BTT) technology is employed to record forced response data. A well-known approach to evaluate the raw data namely times of arrival (TOA) without the availability of a once-per-revolution (OPR) signal is adapted, implemented, and applied for the evaluation. The results are compared to those received by using a commercial evaluation software for BTT measurement data. Finally, the actual gain achieved by means of IM is discussed in detail.
Impact of Effusion Hole Exit Geometry on the Cooling Performance of TBC Coated Surfaces in a High Temperature Combustion Environment
Authors: Snyder Kevin , Boguszewski Matthew , Cetegen Baki M.
Published: September 2023

This study examined the thermal characteristics and cooling performance of effusion cooling configurations by means of laser Rayleigh scattering (LRS) and infrared thermography. Combustor liners exposed to high temperature combustor flow in modern gas turbine engines are designed with advanced effusion cooling configurations to prevent damage and failure of the metal alloy. Thermal barrier coatings (TBCs) are applied to surfaces to reduce the thermal load on metal combustor liners. Effusion cooling hole geometries impact cooling performance and cooling film development. In this study, the impact of effusion jet hole blockage was investigated. An experimental test rig with a bulk vitiated crossflow of 1500K was used to study cooling performance of two effusion cooled plates: one with contracted effusion hole openings, and the other without. Carbon dioxide was used as the coolant over a range of blowing ratios (2.5–12) when the test rig reached quasi-steady operating conditions. Infrared imaging of the cooling array surface indicated higher temperatures for the contracted hole openings. LRS temperature imaging provided planar gas temperature measurements at three heights close the surface of the effusion plate. These gas temperature images were compared between the two plates and show differences in near-wall gas temperatures. The height of cooling film development and approximate near wall heat transfer characteristics were also obtained from these measurements. Average planar gas temperature images obtained in this study showed the plate without contraction allowed coolant to remain closer to the plate surface, improving convective cooling and reducing surface temperature and heat flux. Root-mean-square (RMS) deviation of instantaneous planar gas temperatures was also used to assess the stability of the cooling film at a given height above the surface.
Experimental Investigation of Broadband Noise Sources in a Swirl Stabilized RQL Combustor
Authors: Ha Sungyoung , Dhanasekaran Jananee , Bapat Archit , Acuna Amalique , Patel Shivam , Jo Seunghyun , Wu David , Emerson Benjamin , Steinberg Adam , Lieuwen Tim
Published: September 2023

This paper presents data collected from a model rich-burn, quick-quench, lean-burn swirl-injected single sector combustor. This is part of a larger effort to study the dynamics behind direct and indirect sources of combustor noise. Simultaneous acoustic pressure and OH* chemiluminescence were obtained over a range of conditions, particularly focusing upon the effect of air splits and fuel flow rates upon the broadband acoustic response. Acoustic pressure and chemiluminescence spectra were analyzed and coherence and correlation areas were estimated. Results demonstrate that the equivalence ratio at the primary zone has a significant impact on the frequency response. Higher equivalence ratios led to lower, low frequency broadband noise below 300 Hz but excited a narrowband mode at approximately 650 Hz. Differing the primary and secondary air split ratio but keeping the primary zone equivalence ratio constant showed no significant effect on the broadband noise. The chemiluminescence and acoustic signals showed weak coherence at all frequencies.
A Radio Frequency Polarimetry Sensor for Monitoring Rotor Shaft Position
Authors: Inoue Yuko , Perez Luis E. , Pratt Thomas G. , Morris Scott C.
Published: September 2023

Radio Frequency (RF) sensors are a novel, non-contact measurement technology that offers potential for engine health monitoring. A dual-polarized, distributed RF sensor system was considered here in order to provide information on rotor whirl in an axial compressor test facility. The amplitude of whirl was controlled using a magnetic bearing system. The RF sensor system provided time series information for each transmit/receive antenna combination and RF frequency. A large diversity of responses was observed across the different transmit/receive combinations and RF frequencies. Regression analysis was conducted using a multi-layer neural network. The results demonstrated that rotor whirl radius can be predicted from RF polarimentry measurements using a simple, artificial neural network based regression algorithm.
Investigation of Combustion Oscillation Modes of Hydrogen Micromix Flames
Authors: Kroniger Daniel , Kamiya Hiromu , Horikawa Atsushi
Published: September 2023

The micromix combustion principle is a dry low NOx combustion concept for high hydrogen fuels in gas turbines. In the can-type combustor, where multiple micromix flames are arranged circumferentially, a rotational thermoacoustic oscillation mode has been found. The objective of this study is to investigate combustion instabilities of generic micromix flames with an experimental setup and applying phase-averaged OH chemiluminescence imaging and an acoustic mode analysis. The low-frequency regime longitudinal mode found in the experiment at moderate overload (130%) could be reproduced by large eddy simulations (LES). The mean Rayleigh index and local pressure distribution identifies the initiation of the thermoacoustic instabilities inside the flame zone. A vertical high-frequency oscillation mode, wherein flames of opposed injection direction are interacting and distorting each other, has been experimentally found at high overload conditions (170%). Interestingly, the method of phase averaged imaging reveals that the frequency of the oscillation cycle is actually half of the frequency of the measured dynamic pressure.
High-Fidelity Computational Assessment of Aero-Thermal Performance and the Reynolds’ Analogy for Additively Manufactured Anisotropic Surface Roughness
Authors: Jelly Thomas O. , Abu Rowin Wagih , Hutchins Nicholas , Chung Daniel , Tanimoto Koichi , Oda Takuo , Sandberg Richard D.
Published: September 2023

Direct numerical simulations of incompressible turbulent forced convection over irregular, anisotropic surface roughness in a pressure-driven plane channel flow have been performed. Heat transfer was simulated by solving the passive scalar transport equation with Prandtl number Pr = 0.7. The roughness topographies under investigation here are based on an X-ray computed tomography scan of an additively manufactured internal cooling passage, which had an irregular, multi-scale and mildly non-Gaussian height distribution. Three different roughness topographies and three different friction Reynolds numbers (Reτ = 395, 590, 720) were considered, along with reference smooth-wall simulations at matched Reτ. By systematically varying the roughness topography and flow conditions, a direct computational assessment of aero-thermal performance (pressure losses and heat transfer) and the Reynolds analogy factor, i.e. 2Ch/Cf, where Ch is the heat-transfer coefficient (Stanton number) and Cf is the skin-friction coefficient, was conducted. The results highlight the profound impact that the roughness orientation (relative to the flow direction) has upon the aero-thermal performance of additively manufactured internal passages, with transverse-aligned roughness augmenting heat transfer by as much as 33%, relative to its streamwise-aligned counterpart. An interrogation of velocity and temperature statistics in the near-wall region was also performed, which underlined the growing dissimilarity between heat transfer and drag as fully-rough conditions are approached.
Investigation of the Aerodynamic Losses Caused by the Impeller/Volute Interaction in a Transonic Centrifugal Compressor
Authors: Reymond Loïc Marc , Geilich Marius , Stemmermann Julian , Jeschke Peter
Published: September 2023

The aerodynamic losses caused by the impeller/volute interaction in a transonic centrifugal compressor stage with a vaneless diffuser for turbocharger applications are numerically analyzed. In the operating point investigated a high volute mismatching induces an inhomogeneous pressure profile in circumferential direction with a pressure difference of up to 1 bar at the diffuser outlet, which corresponds to about 20% of the average pressure in this plane. This inhomogeneity propagates upstream and causes unsteady losses in the highly loaded impeller, which are investigated in detail. URANS simulations are conducted to enable a detailed analysis of the highly unsteady flow, evidenced by a high acoustic Strouhal number Sr = 0.18. To model the influence of the volute, an experimentally measured inhomogeneous static pressure profile is used as a boundary condition at the diffuser outlet. At the operating point investigated, the inhomogeneity reduces the time-averaged total-to-static stage efficiency Δηis,ts,4 by up to −1.2%, about two-thirds of which are caused by the impeller, as measured by the entropy increase. The analysis points out a large positive pressure gradient in the direction of rotation at the impeller outlet as the origin of these losses. An interaction region at the impeller outlet is identified using a velocity decomposition in the absolute and the relative frame of reference. The analysis shows that the interaction region impacts the flow inside the impeller significantly causing additional losses and that the identified loss mechanisms are of unsteady origin. Therefore, time accurate unsteady simulations are shown to be necessary for accurately predicting the losses in a centrifugal compressor with a high volute mismatching.
PIV Measurements in a High-Speed Low-Reynolds Low-Pressure Turbine Cascade
Authors: Okada Mizuki , Simonassi Loris , Lopes Gustavo , Lavagnoli Sergio
Published: September 2023

Particle image velocimetry (PIV) measurements in the blade-to-blade (B2B) plane and cascade outlet plane (COP) of a high-speed low-pressure turbine (LPT) cascade were performed. The measurements were performed at engine-representative outlet Mach number (0.70–0.95), and Reynolds number (70k–120k) under steady flow conditions. The freestream turbulence characteristics were imposed by means of a passive turbulence grid.

The PIV results on the B2B plane were compared against five-hole probe (5HP) and Reynolds-averaged Navier-Stokes (RANS) computations to assess the validity of measurement and simulation techniques in the engine-relevant LPT cascade flows. The PIV captured the wake depth and width measured by the 5HP whereas the RANS displayed an overprediction of the wake Mach number deficit. The 5HP was found to impose sinewave fluctuations of the measured flow angle downstream. The variation of fluctuation captured by the PIV was around three times lower. In addition, PIV provided an estimation of the turbulence intensity (TI) in the cascade passage, displaying a decay along a streamline following the passage curvature. For the highest Mach number investigated, a peak in the TI was measured past a shock wave.

Measurements of the outlet flow field highlighted a high TI in the secondary flow region whereas high degree of anisotropy (DA) was registered in the boundary of the secondary flow and freestream regions. The contribution of the streamwise fluctuation component was found to be less than the crosswise and radial components in the freestream region. Increasing the cascade outlet Mach number, the contribution of streamwise fluctuation to the DA was observed to decrease.