bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of Cast, Wrought and LPBF Processed IN718 Concerning Crack Growth Threshold and Fatigue Crack Growth Behavior
Authors: Brune Timo , Kraemer Karl Michael , Kontermann Christian , Oechsner Matthias 
Published: October 2022

Abstract
This study focuses on the influence of microstructure and ductility on the short crack behavior and the FCG threshold. For this, an additively manufactured batch of the nickel-based alloy IN718, made via Laser Powder Bed Fusion (LPBF) process, is compared to both conventionally wrought and cast IN718 material.
An initial characterization revealed significant differences in grain structure, from regular fine grained wrought material to large grains of several millimeters in diameter in the cast variant and a chessboard-like grain structure typical for LPBF. The ductility parameters of IN718-LPBF and wrought IN718 are comparable at room temperature, but at 650 °C the LPBF-variant shows macroscopic brittle fracture.
The fatigue crack behavior both in the short and long crack regime is investigated in air at 650 °C. To produce minimal crack growth increments of about 1 μm, a compressive pre-cracking and subsequent threshold test procedure with step-wise load increase has been adapted for high temperature testing.
To assess the short crack behavior, cyclic R-curves have been generated taking the influence of three different stress ratios (Rσ = −1, 0 and 0.5) into account. As expected, increasing crack closure mechanisms at higher stress ratios lead to higher stress intensity amplitudes ΔKI necessary to initiate crack growth. The crack growth resistance of the LPBF processed variant is higher compared to wrought IN718.
In the long crack regime, the wrought alloy yields higher crack growth rates compared to LPBF and cast IN718. An expected R-ratio dependency is observed for all material states.
Investigation of Water Films Shed From an Airfoil in a High-Speed Flow
Authors: Rodriguez Brandon Esquvias , Hickey Brendan , McDonell Vincent , Tabata Soichiro , Senoo Shigeki 
Published: October 2022

Abstract
The breakup of liquid films in high-speed flows are found in many applications. These include pre-filming air blast atomization found in fuel injectors and shedding of droplet off of airfoils. In this work, a test rig has been developed and applied to study the breakup of water films from the trailing edge of an NACA 0012 airfoil placed in a high-speed air flow. The results provided reflect a new detailed data set focus on air velocities above 75 m/s. Computational fluid dynamic (CFD) simulations were used to guide the development of the rig and the associated boundary and inlet conditions. In the present work, air velocities up to 175 m/s were used with water films between 0.4 and 3.6 cm2/s. The water film was introduced onto one surface through a series of 0.5 mm holes separated by 1mm at a location 35 mm downstream of the leading edge of the vane. High speed video was used to document the sheet breakup behavior from the edge of the airfoil. Image analysis was used to identify the breakup length of ligaments formed. Laser diffraction was used 50 mm downstream of the trailing edge of the vane to determine the droplet size distribution and associated representative average diameters generated. A series of test conditions were run between 50 and 175 m/s using multilevel factorial designed experiments. The results obtained were subject to analysis of variance to generate correlations for breakup length and droplet representative diameters as a function of the conditions studied. The analysis was conducted on dimensionless versions of the variables studied to help connect the results to the physics of the situation. For example, rather than using air velocity to correlate the behavior, the Weber number (based on gas phase density and velocity) was used owing to its historical ability to describe liquid breakup processes. The results obtained are compared with other studies in the literature, and good agreement was found for the conditions at which a comparison could be made. It is observed that, for the conditions studied, liquid film thickness has little effect on the resulting droplet sizes — especially for the higher air velocity cases studied. The results also illustrate the sensitivity to choice of characteristic length, which has generally consisted of trailing edge geometry or boundary layer thickness. In contrast, liquid film does influence the ligament breakup length, although the time to break up is less affected. Overall, the correlations developed provide engineering tools to help estimate ligament and drop size behavior for water films shed from airfoils in a high-speed flow.
Ensemble Learning Approach to the Prediction of Gas Turbine Trip
Authors: Losi Enzo , Venturini Mauro , Manservigi Lucrezia , Bechini Giovanni 
Published: October 2022

Abstract
In the field of gas turbine (GT) monitoring and diagnostics, GT trip is of great concern for manufactures and users. In fact, due to the number of issues that may cause a trip, its occurrence is not infrequent, and its prediction is a quite unexplored field of research. This is demonstrated by the fact that, despite its relevance, a comprehensive study on the reliability of predicting GT trip has not been proposed yet.
To fill this gap, this paper investigates the fusion of five data-driven base models by means of voting and stacking, in order to increase base model accuracy and improve prediction robustness. The five benchmark supervised Machine Learning and Deep Learning classifiers are k-Nearest Neighbors, Support Vector Machine, Naïve Bayes, Decision Trees, and Long Short-Term Memory neural networks. While voting just averages the predictions of base models, without providing additional pieces of information, stacking is a technique used to aggregate heterogeneous models by training an additional machine learning model (namely, stacked ensemble model) on the predictions of the base models.
The analyses carried out in this paper employ filed observations of both safe operation and trip events, derived from a large fleet of industrial Siemens GTs in operation.
The results demonstrate that the stacked model provides higher accuracy than base models and also outperforms voting by proving more effective, especially when the reliability of the prediction of base models is poor.
Experimentally Validated Design of an Anode Recirculation Blower for PEM Fuel Cells Under Variable Fluid Composition
Authors: Nachtigal Philipp , Kentschke Thorge , Seume Joerg R. 
Published: October 2022

Abstract
This paper focuses on the design, construction and the experimental testing of an anode recirculation blower (ARB) based on a turbo-compressor for PEM-FCs. The blower presented consists of a high-speed centrifugal compressor, driven by a so-called media-gap motor. Additionally it includes a droplet separator to eliminate liquid water from the anode loop. The aerodynamic design is based on 1D-correlations and 3D-numerical CFD simulations. Different gas compositions of hydrogen, nitrogen and water vapor are considered in the design, depending on the operating points of a PEM-FC. The gas composition has a significant influence on the achievable pressure ratio at constant compressor speeds, depending mainly on the specific heat capacity of the gas. Performance maps for different gas compositions are calculated using CFD for the designed ARB. A prototype is built and tested. The results validate the CFD predictions and show that the operating range of a PEM fuel cell can be covered with the present blower. In addition, it could be shown that an enthalpy-based approach using common characteristic numbers of turbomachines, allows converting performance maps — acquired with different gas compositions — into one another. This allows the performance map prediction for different gas compositions based on existing performance maps. This approach is illustrated by numerical and experimental results.
Comparison of Flame Describing Functions Measured in Single and Multiple Injector Configurations
Authors: Rajendram Soundararajan Preethi , Durox Daniel , Vignat Guillaume , Renaud Antoine , Beaunier Jérôme , Candel Sébastien 
Published: October 2022

Abstract
Recent investigations of combustion instabilities in annular systems indicate that considerable insight may be gained by using information gathered in single-sector experiments. Such experiments are, for example, employed to measure flame describing functions (FDFs), which represent the flame response to incident perturbations. These data may be used in combination with low-order models to interpret instabilities in multiple injector annular systems. It is known, however, that the structure and dynamical behavior of an isolated flame do not necessarily coincide with those of a flame placed in an annular environment with neighboring side flames. It is then worth analyzing effects that may be induced by the difference in lateral boundary conditions and specifically examining the extent to which the FDF data from single-segment experiments portrays the dynamical response of the flame in the annular environment. These issues are investigated with a new setup, named TICCA-Spray, that comprises a linear arrangement of three injectors. The central flame is surrounded by two identical side flames in a rectangular geometry with key dimensions, side-wall separation, and spacing between injectors identical to those of the annular system MICCA-Spray. The describing function of the central flame is determined with techniques recently developed in single sector experiments (SICCA-Spray). The FDFs obtained in the two configurations are compared for two swirler types having different swirl numbers and pressure drops. The effect of the swirl direction of the neighboring injectors is also explored by operating with co- and counter-swirl combinations. Differences between FDFs determined in the two test facilities, sometimes modest and in other cases less negligible, are found to depend on the flames’ spatial extension and interactions. The general inference is that the FDFs measured in a single-injector combustor are better suited if the flame-wall interaction is weak, and provided that the area is equivalent to that of a single sector of an annular combustor. Nonetheless, using a multi-injector system would be more appropriate for a more precise FDF determination.
Mistuning and Damping of a Radial Turbine Wheel. Part 2: Implementation and Validation of Intentional Mistuning
Authors: Nakos Alex , Beirow Bernd , Zobel Arthur 
Published: October 2022

Abstract
A radial turbine impeller of an exhaust turbocharger is analyzed in view of both free vibration and forced response. Due to random blade mistuning resulting from unavoidable inaccuracies in manufacture or material inhomogeneities, localized modes of vibration may arise, which involve the risk of severely magnified blade displacements and inadmissibly high stress levels compared to the tuned counterpart. Contrary, the use of intentional mistuning (IM) has proved to be an efficient measure to mitigate the forced response.
In part 1 of this three-part paper fundamental analyses have been carried out to find a suitable intentional mistuning pattern featuring only two different blade designs [1]. This part is focused on the implementation and validation of the intentional mistuning pattern and discusses the detailed geometric adaption of the turbine wheel hardware. The final design of the geometric adaption is developed in terms of manufacturability and efficiency so that a reliable and robust solution is presented. Its machined adaption is validated by both vibration testing at rest and optical measurements so that manufacturing deviations are detected and their impacts discussed and evaluated. Reduced order models are built up for checking the effect of the implemented intentional mistuning pattern on the forced response by using the subset of nominal system modes (SNM) approach introduced by Yang and Griffin [2], which conveniently allows for accounting both the design intention of the mistuning pattern and the actually machined implementation due to manufacturing deviations.
Assessment of RANS Turbulence Models on Simplified Geometries Representative of Turbine Blade Tip Shroud Flow
Authors: Uncu Fatih , François Benjamin , Buffaz Nicolas , Le Guyader Sébastien 
Published: October 2022

Abstract
RANS turbulence models are assessed here in simulations of simplified configurations representative of geometries and flows found in tip shrouds of low-pressure turbines rotor blades. The complex flow inside a tip shroud is highly turbulent, its boundary layer separates at the sharp angled tangential fins and reattaches in the inter-fin cavity after a recirculation. The flow in the tip seal of the rotor blade, and the jet mixing flow at the exit of the shroud cause pressure losses and influence substantially the aerodynamic performance of the turbine. Such flows are quite challenging for the RANS models. The main aim of this paper is to assess the capability of the used turbulence models to predict tip shroud representative physics of detached, reattached and jet mixing flows. The simplified geometries consist of a backward facing step, a rib roughened channel and a jet in cross-flow. The Reynolds numbers of these configurations are close to those estimated in real tip shrouds. Experimental data are available in each case to evaluate the accuracy of the simulations and understand the behavior of the models. The evaluated turbulence models include several widely used eddy-viscosity models based on Boussinesq’s hypothesis and a differential Reynolds stress model. Comparisons with measured components of the Reynolds stress tensor, turbulent kinetic energy and velocity profiles are presented. The velocity profiles are in good agreement with the measurements except in the recirculation regions, and eddy-viscosity models overpredict the level of experimental turbulent kinetic energy. Analysis of the strengths and weaknesses of the models for each flow are discussed.
Numerical Simulations of a Lifted Hydrogen Jet Flame Using Flamelet Generated Manifold Approach
Authors: Xia Yu , Verma Ishan , Nakod Pravin , Yadav Rakesh , Orsino Stefano , Li Shaoping 
Published: October 2022

Abstract
A turbulent lifted H2/N2 jet flame in a vitiating co-flow environment is numerically investigated, using the Flamelet Generated Manifold (FGM) combustion model with Large Eddy Simulations (LES). Due to the hot vitiated H2/air co-flow, the primary stabilization mechanism is the autoignition followed by a premixed flame. In addition to using H2 as a fuel, this flame poses two other modeling challenges: (i) the autoignition, which is a transient chemistry-driven phenomenon; (ii) the existence of multiple combustion regimes, e.g., diffusion at autoignition location but premixed in the post flame. A series of LES/FGM simulations are completed in this work by reducing the co-flow temperature from 1045 K to 1000 K. The FGM model can predict the characteristics of the flame by showing a lifted flame. It also accurately predicts the trend in the flame lift-off distance with a change in the co-flow temperature. The current results are compared for mixture fraction, temperature, and OH mass fraction at multiple locations, which have also been correctly captured. It is noted that for a high co-flow temperature (and hence a low lift-off distance), the flame’s lift-off is highly sensitive to the inlet boundary conditions and the mesh resolution near the jet entry. A relatively coarse mesh is used for all the simulations, which is generated using a careful strategy that not only resolves the jet instabilities near the fuel inlet, but also keeps the overall mesh count low and allows for a large computational time step. A systematic sensitivity analysis on the computational speed is also performed. This work provides some useful guidelines in simulating the H2 diluted flames using the FGM model, which may be valuable to the gas turbine industry.
Numerical Investigation on the Effect of Fuel Injection Location in a Multi-Swirl Lean Direct Injection Burner
Authors: Sarath Perikathra , Aditya Raparti Jogesh , Muruganandam T. M. 
Published: October 2022

Abstract
The lean direct injection (LDI) concept can potentially replace the existing combustion systems for future aircraft engines because of its low NOx emissions without compromising other parameters. A novel multi-swirl LDI burner1 with distributed fuel injection surrounded by airflow through multiple hexagonal swirlers of vane angle 45° was developed. The flow dynamics and combustion characteristics of three different fuel injection LDI configurations were compared using a three-dimensional (3D) computational fluid dynamic (CFD) study. Realizable k-ε turbulence model with a scalable wall function was adopted to get the flow features, distribution of velocity, pressure, and turbulent kinetic energy in the swirl burner, and combustion was parameterized by using non-premixed steady diffusion flamelet model with a PDF approach. Results obtained in the numerical model for temperatures and mole fractions of CO2, O2, and mass fraction of NOx show a behavior similar to that of the experimental model. Four types of flow structures were present in the flow field, and interaction of these structures plays an essential role in rapid mixing and flame stabilization. The numerical results showed that the LDI-2A burner achieved better mixing and had a lower flame temperature than the other two burners, which would improve flame stability and reduce the NOx emission.
Hysteresis and Bi-Stability in Transversely Excited Swirling Flows
Authors: Gupta Ravi , Gohiya Rajat , Vempati Chandan , Hemchandra Santosh , Panda Pratikash 
Published: October 2022

Abstract
In this work, we investigate the effect of transverse acoustic excitation on non-reacting swirling jets. The work is motivated by the azimuthal instabilities in annular gas turbine combustors which are one of the major challenges in aero-engines. Annular combustion chambers have a longer circumferential length in comparison to their length or height. As a result, thermoacoustic instabilities are driven by azimuthal acoustic modes. We have designed and fabricated a multi-nozzle (up to three nozzles) linear array combustor to simulate the flow conditions of an annular combustor. The nozzle features a dual co-rotating radial swirler, with a flow split of 44% and 56% between the primary and secondary swirlers. Two compression drivers (power 400 W each) placed on either side of the combustion chamber are used to generate acoustic fields in the direction transverse to the flow. Simultaneous 2D PIV and high-frequency pressure measurements are conducted to measure the time-averaged velocity field and the chamber acoustics, respectively. The time-averaged flow field of the quiescent swirling jet shows a typical low swirl number flow-field that features a narrow recirculation zone surrounded by a high-velocity annular jet. It is observed that once the swirling jet is excited with a transverse acoustic forcing, it instantaneously transitions to a conical type of vortex breakdown (CVB). However, this phenomenon is observed only above a threshold value of perturbation amplitude. In this condition, the flow moves radially outward and remains attached to the walls on either side of the nozzle, and is characterized by a recirculation zone with strong a negative axial velocity. It is a known phenomenon that swirling jets transition to a CVB upon transverse acoustic excitation. However, to the best of our knowledge, this is the first instance where it is shown that transverse acoustic excitation can lead to a bistable state in swirling flows. We investigated the acoustic response to low-amplitude forcing on the combustion chamber by performing a forced acoustic response analysis using COMSOL. It is observed that acoustic forcing leads to a peak response of the radial and azimuthal velocities at the flare of the swirler, which could induce an axisymmetric deflection of the jet shear layer pushing it into a CVB state. In the case of a multi nozzle array of three identical swirlers, we observed that the external acoustic forcing changes the time averaged base flow of the central nozzle.
Extension of Fuel Flexibility for Siemens Energy SGT-300-2S Dry Low Emission Combustion System
Authors: Hubbard Phill , Beita Jadeed , Liu Kexin , Sadasivuni Suresh , Bulat Ghenadie 
Published: October 2022

Abstract
This paper reports the results of high-pressure combustion rig testing carried out to assess the fuel flexibility of the standard Siemens Energy SGT-300-2S dry low emission (DLE) combustion system operated at engine conditions across a wide range of engine loads and ambient conditions. Variations of the fuel heating value, with Wobbe Index (WI) of 23 MJ/Sm3, 25 MJ/Sm3, 27.5 MJ/Sm3, 30 MJ/Sm3 and 45 MJ/Sm3 (UK natural gas) at standard conditions1, were achieved in a mixing plant by blending natural gas with CO2 as diluent. Emissions, fuel pressure, combustion dynamics, and flashback monitoring via measurement of burner and combustor can metal temperatures were the main parameters used to assess the effect of fuel flexibility on combustor performance. Test results show that NOx emissions decrease as the fuel heating value is reduced due to lower adiabatic flame temperatures for the MCV (Medium Calorific Value) fuels. CO emissions performance was found to be unaffected. However, decreasing fuel heating value leads to a requirement to increase the fuel supply pressure as a consequence of higher volumetric fuel flow rate to achieve the heat input requirements of the gas turbine. Combustion dynamics characteristics were found to be similar for the different fuel compositions. The impact of fuel heating value change on turbine nozzle guide vanes and blades was also investigated by measuring the combustion hot gas temperature profile at the exit of transition duct. The results show that there is no significant change in turbine entry temperature profile in terms of maximum temperature and pattern factors.
The successful development program has expanded the capability of the SGT-300-2S standard production DLE combustor to operate with a range of fuels covering a WI range of 25 MJ/Sm3 to 49 MJ/Sm3. The test results obtained on the SGT-300-2S combustion system provide significant experience for industrial gas turbine burner design for fuel flexibility.
Investigation of the Interaction Between Tip Leakage and Main Annulus Flow in the Large Scale Turbine Rig: Comparison of Different Rotor Tip Geometries
Authors: Ade Dominik , Eitenmüller Johannes , Leichtfuß Sebastian , Schiffer Heinz-Peter , Lyko Christoph , Schmid Gregor 
Published: October 2022

Abstract
Shroudless rotor blades are state of the art in modern high pressure turbines. Tip leakage flow has a crucial impact on turbine efficiency. Specific blade tip designs are a key factor to handle tip leakage losses by controlling tip leakage flow and its re-entry into the rotor passage.
Comparative measurements of a cavity squealer type tip and a notch type tip have been conducted at the Large Scale Turbine Rig at TU Darmstadt. The test rig has been operated at the blade tips design point. Experimental data has been acquired at rotor inlet and outlet as well as within the rotor passage.
For cavity squealer tips a tip leakage vortex develops at the suction side as the tip leakage flow is rolled-up and further mixed with main annulus flow. The tip leakage vortex determines the blockage of main annulus flow at the blade tip. The design of the suction side of the notch tip benefits a jet-like re-entry of tip leakage flow into the passage. Results are a vortex system with smaller scaled vortices and a more homogeneous mass flow redistribution in the outer annulus of the rotor. The zone of affected main annulus flow at the blade tip increases through the dominant tip leakage jet.