bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Interaction of Purge Flows With Secondary Flow Features in Turbine Center Frames
Authors: Patinios Marios , Merli Filippo , Hafizovic Asim , Göttlich Emil 
Published: September 2021

Abstract
The turbine center frame (TCF) is an inherent component of modern turbofan aircraft engines, used for facilitating the large radius change between the high-pressure (HPT) and low-pressure (LPT) turbines. Secondary flow features that develop in the TCF result in total pressure loss of the mainstream flow and a subsequent performance reduction for the whole of the engine. Purge flows from the HPT interact with these flow features affecting their development and strength. Understanding the details of this interaction is therefore of paramount importance for the design of more efficient engines of the future.
This paper presents a detailed investigation of the interaction of purge flows from the hub and shroud cavities upstream and downstream of the HPT rotor with the secondary flow features in a TCF. The investigation was conducted using aerodynamic and seed gas concentration measurements in an engine-representative HPT-TCF setup and under engine-realistic operating conditions.
The upstream purge flows interact with the flow-field of the rotor, and especially with the upper and lower passage vortices where they are mainly entrained, forming “zones-of-influence” that occupy the upper and lower 35% of the span at the TCF inlet. Dilution of these purge flows occurs through vortex-to-vortex interactions and in-plane flow migrations driven by the vortices. At the outlet of the TCF, the upstream purge flows form effectiveness bands that encapsulate the various counter-rotating vortices near the hub and shroud. This indicates that these counter-rotating vortices were formed at the inlet of the TCF, in a flow that already includes the upstream purge flows.
The downstream purge flows exit the hub and shroud cavities forming effectiveness boundary layers at the inlet of the TCF of thickness equal to around 15% of the span. The circumferential distribution of these purge flows is however asymmetric, owing to the also asymmetric static pressure distribution at the inlet of the TCF, as a result of the effect of the propagated flow-field of the stator vanes.
At the outlet of the TCF, the distribution of the downstream hub purge appears as distinct effectiveness lobes with the same periodicity as the HPT vanes. The formation of the lobes is as a result of intense interaction between the counter-rotating vortex pairs and the downstream hub purge flow. The viscous shear mixing due to this interaction is also the cause for the low total pressure in the regions influenced by the lobes. The distribution of the downstream shroud purge appears as alternating regions of high and low effectiveness as a result of radially inwards and outwards flow migrations caused by the shearing actions of the counter rotating vortices near the shroud. These migrations are the cause of regions with the lowest total pressure at the outlet of the TCF.
Axial-Radial Diffuser With Integrated Exhaust Hood for An Automotive Turbocharger With Axial Turbine
Authors: Kuestner Christoph , Seume Joerg R. 
Published: September 2021

Abstract
Exhaust hoods with an integrated axial-radial diffuser use the kinetic energy downstream of a turbine for static pressure recovery. This is especially useful in applications with limited axial space behind the turbine. So far, such exhaust hoods have been used almost exclusively in larger turbomachinery such as maritime turbochargers and steam turbines, where an axial turbine is typically installed. In combination with an axial turbine, an exhaust hood can result in a very powerful and space-efficient turbine design, especially under highly pulsating inflow conditions. Both are important requirements for automotive turbochargers. Therefore, the application of such an exhaust hood in a small automotive turbocharger is investigated in this paper; this turbocharger also uses an axial turbine. In the first step, a preliminary design is developed, based on a design approach for steam turbine exhaust hoods. The resulting design is examined with a 3D CFD model to determine efficiency and turbine performance. Subsequently, the design is improved by modifying the exhaust hood geometry such as to further improve the overall efficiency of the turbine. Finally, the CFD evaluation for the operating point investigated reveals an increased power output and a higher overall turbine efficiency compared to the initial design. A resulting design guideline for exhaust hoods with an integrated axial-radial diffuser is included.
Uncertainty Quantification of a Jet Engine Performance Model Under Scarce Data Availability
Authors: Ludwig Norbert , Antinori Giulia , Daub Marco , Duddeck Fabian 
Published: September 2021

Abstract
The development of jet engine components requires a detailed quantification of different uncertainty sources to improve the quality and robustness of the design. In order to get a better understanding of the entire interdisciplinary jet engine design process, the detailed uncertainty quantification of the performance parameters is of vital importance. This paper demonstrates a new approach how to represent the uncertainties in a jet engine performance model caused by the manufacturing and assembly process. In earlier research studies, the manufacturing process was modeled with a probabilistic approach, i.e. by assuming a multivariate normal distribution for the corresponding parameters. Within the scope of this paper, the uncertainty of the components’ flow capacity and efficiency is quantified based on a limited set of data. Due to the extreme scarcity of the data set, it is proposed to use methods from the field of non-probabilistic uncertainty quantification. In this paper, three different approaches to derive the variation of the components’ flow capacity and efficiency are compared with each other. In contrast to probabilistic methodologies, all approaches are able to represent the lack of data without making any additional assumptions regarding the underlying type of distribution. As a result, each of the methodologies describes the uncertain parameters by probability-boxes. After clarifying the theoretical background, the results obtained from the different approaches are discussed in detail. It figured out that the propagation method for probability-boxes plays a crucial role for the uncertainty quantification.
Experimental Investigation of the Confinement Effects in Radial-Radial Swirlers
Authors: Kıyıcı Fırat , Perçin Mustafa 
Published: September 2021

Abstract
This experimental study investigates the effect of confinement ratio (CR) on the flow field of a counter-rotating radial-radial swirler. Two-dimensional two-component (2D2C) particle image velocimetry (PIV) measurements are performed at the mid-plane of the jet. Four different confinement ratios (i.e., 10.4, 23.4, 41.6 and unconfined) are considered at a swirl number of 1.2. The results reveal the presence of a central toroidal recirculation zone (CTRZ) in all cases extending inside the jet which indicates the existence of an adverse pressure gradient. For the unconfined swirling jet, the recirculation zone is small in size and exists at the exit of the jet. For the CR = 41.6 case, on the other hand, there exist two separate recirculation zones with the first one being similar to the unconfined case in terms of size and axial position, while the second one being larger in size and positioned at a more downstream location. Variation of the axial velocity along the centerline of the jet for this case indicates the presence of an adverse pressure gradient only in the close-jet region correlated with the first recirculation zone. For the smaller CR values, a single massive CTRZ emerges. This leads to increase in the expansion angle of the swirling jet as the CR decreases. Correspondingly, the radial velocity at the jet exit increases. For the confined cases with a single recirculation zone, the length and the width to cross-section ratio increase with the CR. On the other hand, the ratio of the reverse flow rate to total mass flow rate decreases with increasing CR values.
Highly Resolved Simulations of a CDA Compressor Cascade: Effect of Reynolds Number on Losses
Authors: Leggett John , Sandberg Richard D. 
Published: September 2021

Abstract
The Reynolds number effects on performance of a Controlled Diffusion Airfoil (CDA) geometry in a linear compressor cascade setup are presented. A set of highly-resolved Large Eddy Simulations at Reynolds numbers from 300,000 to 1,000,000 at a Mach number of 0.7 are performed, with one of the simulations including incident wakes at engine relevant reduced frequency of 1.56. The focus of this work is to investigate loss variation of a modern blade geometry by applying both the novel entropy analysis introduced by (Zhao & Sandberg, GT2019-90126) and the mechanical work potential analysis by Miller (GT2013-95488) in the form presented by Leggett et al. (GT2019-91253). The loss analysis, applied both to the whole blade, and to carefully selected subvolumes, including suction and pressure surface boundary layers, highlights regions of increased loss production and the effects of Reynolds number on the location and strength of different flow processes, such as transition and separation. The results are further broken down to show the contribution to loss of individual terms of the analyses and the changes that occur due to changes in Reynolds number. The effects of incident wakes are also captured using this analysis technique and detailed in the paper.
Data-Driven Analysis of Engine Mission Severity Using Non-Dimensional Groups
Authors: Brandes Tim , Scarso Stefano , Koch Christian , Staudacher Stephan 
Published: September 2021

Abstract
A numerical experiment of intentionally reduced complexity is used to demonstrate a method to classify flight missions in terms of the operational severity experienced by the engines. In this proof of concept, the general term of severity is limited to the erosion of the core flow compressor blade and vane leading edges. A Monte Carlo simulation of varying operational conditions generates a required database of 10000 flight missions. Each flight is sampled at a rate of 1 Hz. Eleven measurable or synthesizable physical parameters are deemed to be relevant for the problem. They are reduced to seven universal non-dimensional groups which are averaged for each flight. The application of principal component analysis allows a further reduction to three principal components. They are used to run a support-vector machine model in order to classify the flights. A linear kernel function is chosen for the support-vector machine due to its low computation time compared to other functions. The robustness of the classification approach against measurement precision error is evaluated. In addition, a minimum number of flights required for training and a sensible number of severity classes are documented. Furthermore, the importance to train the algorithms on a sufficiently wide range of operations is presented.
GPU-Enabled High-Fidelity LES Simulations for Turbomachinery Flows
Authors: Osusky Michal , Bhaskaran Rathakrishnan , Kapilavai Dheeraj , Sluyter Greg , Shankaran Sriram 
Published: September 2021

Abstract
Engineers performing computational simulations of flow physics are often faced with a trade-off between turn-around time and accuracy. High-fidelity models that can accurately capture small details of flow, such as turbulent mixing, are typically too expensive and are therefore reserved for studying smaller, component level problems. Standard models, like Reynolds-Averaged Navier-Stokes (RANS) and Unsteady-RANS, are used to predict larger interactions without the ability to accurately compute the small scales, at a lower computational cost than high-fidelity models. However, with specific algorithmic choices and access to large-scale GPU systems, we can demonstrate high-fidelity simulations of large engine sections that can be completed within engineering design cycle turn-around times, instead of the typical weeks to months required for high fidelity simulations.
In this paper we present the high-order GENESIS code, employed in the simulation of complex turbulent flows inside the high-pressure turbine of a jet engine. The code efficiently exploits GPU accelerators to execute high-fidelity simulations, while also demonstrating extraordinary accuracy validated by experimental data and previous RANS model predictions. This is demonstrated for a three-dimensional high-pressure turbine stator domain, for which the LES is able to accurately predict wake mixing and temperature distribution, factors that are critical for designing durable turbine components.
The new capability allows for computational studies of phenomena such as laminar to turbulent transition and wake mixing, all applied to relevant three-dimensional geometries present in the high-pressure turbine, all within the time scale of a typical engineering design cycle.
A Method for Establishing the Central Crack Stress Intensity Factor Database for Probabilistic Risk Assessment Based on the Universal Weight Function
Authors: Xu Tongge , Ding Shuiting , Zhou Huimin , Li Guo 
Published: September 2021

Abstract
Probabilistic failure risk assessment is becoming important in the field of airworthiness. In the fracture mechanics module of probabilistic failure risk assessment, it is important to efficiently and accurately calculate the stress intensity factors (SIFs). At present, the weight function method (WFM), especially the universal weight functions (UWFs) proposed by Glinka and Shen, has been adopted to calculate SIFs with high accuracy and computational efficiency. However, the concrete coefficients in the universal weight functions remain unknown, and the rules of the geometry parameters and these coefficients have not yet been summarized, which hinders their subsequent use. In this article, the specific type of embedded crack-central crack is under discussion, and the derivation of the UWF is introduced. The response surface method (RSM), as a means of database establishment, is used to construct the relations between the geometric parameters including the length and thickness of a three-dimensional finite plate and coefficients in the UWF. The errors of the SIF calculation between the UWF and finite element results are less than 2 MPa m within a certain range. For the evaluation of the boundary effect on central cracks, the difference between finite and infinite plates is discussed. In addition, considering the complexity of the general off-centre crack, an approximation method has been proposed to transform the off-centre crack to the central crack. The results show that the method can be applied with high precision in specific situations and stresses the necessity of follow-up research on general off-centre cracks.
Numerical Model for Condensing Steam Through Labyrinth Seal
Authors: Devi Ravindra G. , Seshadri Satyanarayanan , Michelassi Vittorio 
Published: September 2021

Abstract
This paper presents the flow physics of condensing steam flow across a straight through labyrinth seal from numerical simulations performed using ANSYS CFX. Homogeneous nucleation model and droplet growth model, which are critical in predicting condensation, are validated with good agreement against a well-known experimental data set from convergent-divergent nozzle. Validation data includes static pressure drop, condensation location, condensate mass fraction and Sauter mean radius. CFD study is performed on a five teeth labyrinth geometry to predict leakage flow rate, location of condensate accumulation and condensation rate. Impact of subcooled and condensed steam on leakage flow, pressure and temperature field are also discussed. For condensing steam, the condensate accumulation trend is identified. Some of the key findings and physical insights of interest to the designer are listed including: the effect of cooling on the leakage flow (with and without condensation) and the minimum seal wall temperature to avoid condensation based on subcooling needed for droplet formation (at location condition). Also investigated is whether steam condensation continues or if existing condensate evaporates in the downstream pockets, and the effect of heat release from condensation on number of droplets formed and the Sauter mean radius.
Transient Thermoacoustic Responses of Methane/Hydrogen Flames in a Pressurized Annular Combustor
Authors: Ahn Byeonguk , Indlekofer Thomas , Dawson James , Worth Nicholas 
Published: September 2021

Abstract
The present article experimentally investigates the triggering and transient growth of azimuthal instabilities in a pressurized laboratory-scale annular combustor featuring twelve methane/hydrogen flames, as the equivalence ratio is ramped up and down. The ramping rate of equivalence ratio is varied to examine its effect on the transient thermoacoustic response and the driving mechanisms, highlighting a number of previously unseen features.
As the equivalence ratio is dynamically increased, all cases were observed to feature a distinct modal trajectory, during the onset of high amplitude instabilities. Strongly spinning counter-clockwise modes are first excited before a dynamic transition to strongly spinning clockwise modes occurs. Furthermore, the strength of the spinning mode (quantified through the spin ratio or nature angle) was shown to feature a local minima before the spinning mode stabilized in the system, which corresponds to an almost pure spinning state. Hysteresis behaviour was observed in both the amplitude and nature of the mode, resulting in different thresholds for the onset and decay of the instability, depending on the time history of the combustor. Increasing the ramping rate was found to reduce the amount of hysteresis in the system. Furthermore, the high amplitude of the instability resulted in significant harmonic components. The behaviour of the harmonics generally resembles the fundamental component, albeit with some notable exceptions.
Microstructure of IN738LC Fabricated Using Laser Powder Bed Fusion Additive Manufacturing
Authors: Menon Nandana , Hassan Mahdi Tanjheel , Basak Amrita 
Published: September 2021

Abstract
Nickel-base superalloys are extensively used in the production of gas turbine hot-section components as they offer exceptional creep strength and superior fatigue resistance at high temperatures. Such improved properties are due to the presence of precipitate-strengthening phases such as Ni3Ti or Ni3Al (γ′ phases) in the normally face-centered cubic (FCC) structure of the solidified nickel. Although this second phase is the main reason for the improvements in properties, the presence of such phases also results in increased processing difficulties as these alloys are prone to crack formation. In this work, specimens of IN738LC are fabricated on a Coherent Creator laser powder bed fusion (L-PBF) additive manufacturing (AM) equipment. Optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-Ray diffraction (XRD) are carried out to characterize the deposit region. Metallurgical continuity is achieved in the entire deposit region and the specimens do not show any warpage. However, the specimens show voids (e.g., pores and cracks) in the deposit region. The results show that the percentage void area decreases along the build height direction. The deposited IN738LC shows polycrystalline grains in the entire deposit region as confirmed by XRD and EBSD. The grain size also shows variations along the build direction. In summary, the results open opportunities for academic researchers and small-scale businesses in fabricating high-γ′ nickel-base superalloys on a desktop laser powder bed fusion AM equipment.
Study on Relationship Between Dislocation Density and Creep Strain Rate of Single Crystal Ni Based Superalloy for Gas Turbines Using the Discrete Cosine Transform
Authors: Hiraguchi Hideo 
Published: September 2021

Abstract
The discrete cosine transform (DCT) is known to be able to express the relation curve between creep strain and time, or the relation curve between creep strain rate and time very well. Moreover, recently it has been found out that the DCT can draw electron density distribution maps of crystals. In addition, the DCT always passes through all the points measured at an equal interval in any continuous curves and its interpolated values between adjacent points are very reasonable. Furthermore, a new prediction method for long term creep curves from short term creep data by using the DCT was reported at TurboExpo2020. Up to the present, the strength of single crystal Nickel based superalloys for gas turbines at elevated temperatures has been advanced by controlling the interface dislocation density and the lattice misfit at the γ/γ’ interfaces. For this reason, it has to be understood how to evaluate a relationship between interface dislocation density and creep strain rate to develop more advanced single crystal Nickel based superalloys. Therefore, in this research it was studied how to evaluate the relationship between interface dislocation density and creep strain rate of a single crystal Nickel based superalloy for gas turbines by using the DCT. As a result, useful properties on the effective stress have been obtained from the coefficients of the DCT.
Experimental Investigation Into Gravity Drained Journal Bearings
Authors: Khattar Rohit , Bosu Sudeep , Akki Kashinath , Paspulati Amit 
Published: September 2021

Abstract
Turbomachines with large & heavy rotors have journal bearings that utilize thin hydrodynamic oil film to maintain a gap between the shaft & bearings. They are fed with a continuous supply of lube oil at a high rate to maintain the oil film and remove the heat generated. The shaft imparts high rotational velocities to the oil as it passes through the bearing. Due to high kinetic energy of oil leaving the bearing, gravity drained bearing housings generally have a big sump near the bottom dead center to collect and reduce the kinetic energy of the oil. This facilitates smooth drain of oil back to the oil tank. The use of gravity to facilitate the draining results in a simple and cost-effective bearing system. The size of sump is determined by the oil flow rate in the bearing housing which itself is a function of rotor load, speed & temperature. In absence of this oil sump (in applications where there is little or no room for a large bearing housing) the swirling oil in the bearing housing doesn’t get enough time to slow down. The rapidly swirling oil therefore fails to drain into the drainpipe(s), and eventually floods the housing and leaks out through the shaft seals. The failure to drain can be attributed to multiple reasons like air pressure fluctuation, oil vortex formation, oil frothing, etc.
This paper focusses on the design of a journal bearing for gas turbines without an oil sump due to design space restrictions. The flow fields in the bearing are chaotic and difficult to analytically predict without experimental validation. Therefore, a bearing rig was constructed, and multiple tests were conducted to understand the flow characteristics inside the bearing housing. Based on the understanding of the flow characteristics, design modifications were made and validated to enable the design of a sumpless gravity drained bearing housing. This paper discusses the methodology and findings from these rig tests which led to the design solutions that solved the issue of draining the high energy oil back to the oil tank without the need of having a traditional oil sump.