bluuebunny/crossref_metadata_2025 huggingface dataset:
Feasibility Study on the Effect of Blade Inclination for Heavy Duty Centrifugal Fans – Aerodynamic Aspects
Authors: Biedermann Till M. , Moutamassik Youssef , Kameier Frank
Published: September 2021

With a special focus on the industrial feasibility and the manufacturability, a recently proposed novel approach to centrifugal impeller blade inclination is adopted and investigated through extensive CFD analysis. The fan blades, originally aligned perpendicular to the impeller backplate, are inclined in either forward or backward direction. For the presented study, an industrially proven fan design is chosen for testing. Compared to the original design, the inclined fan blades possess an increased total blade area and at the same time providing variable inflow angles at the leading edges of the blades. These two factors are expected to alter the fan characteristic curves in providing an increased range of optimum performance while maintaining high aerodynamic efficiency. The results obtained show a clear trend in aerodynamic performance with the degree of inclination, where the characteristic curves rotate at about the design point, allowing local improvements either at overload conditions or part-load conditions of the fan. Moreover, the trends obtained show the tendency to agree well with the rudimentary models published in previous studies, even though it appears to be affected by the fan volute and the point of operation as well.
Multidisciplinary Sensitivity Analysis of the Cooling System of a High-Pressure Turbine Blade in the Pre-Design Phase
Authors: Fiedler Barbara , Muller Yannick , Voigt Matthias , Mailach Ronald
Published: September 2021

The engine-cycle performance of jet engines can be improved by more efficient cooling systems, either by reducing the required cooling air or by intensifying the cooling efficiency with the same amount of cooling mass flow. However, the multitude of geometrical design parameters and the strong multidisciplinary aspect of cooling mass flow consumption optimization make designing the cooling systems extremely challenging. Integrating probabilistic methods into the thermal design process enables the automated evaluation of multiple design variants which contributes to the development of more efficient systems.

In the present study, the sensitivity of a multi-pass cooling system to geometric variations is investigated. The cooling air flow, solved using a 1D, correlation based flow solver, is iteratively coupled with the 3D-FE thermo-mechanical analysis of the blade. The geometry of the cooling system is varied using the Harmonic-Spline-Deformation parametric, which has been extended to modify the wall thickness enabling to perform a geometrical-holistic analysis. Furthermore, the Elementary-Effects-Method (EEM) and the Monte-Carlo-Simulation (MCS) are compared to identify the most influential parameters and analyze their complex interactions. It is shown that the cooling system’s performance is mostly affected by the shape and position of the first web. Furthermore, MCS proves to be robust towards changes in design space while simultaneously enabling a more detailed analysis of the system behavior compared to EEM.
A Comprehensive Analytical Shock Loss Model for Axial Compressor Cascades
Authors: Banjac Milan , Savanovic Teodora , Petkovic Djordje , Petrovic Milan V.
Published: September 2021

The approach applied in various research papers that model compressor shock losses is valid only for certain types of airfoil cascades operating in a narrow range of working conditions. Lately, more general shock loss models have been established that cover a wider variety of airfoils and operating regimes. However, owing to the complexity of the studied matter, the majority of such models are, to a certain extent, presented only in a descriptive manner. The lack of specific details can affect the end results when such a model is utilized since improvisation cannot be avoided. Some models also apply complex numerical procedures that can slow the calculations and be a source of computational instability. In this research, an attempt has been made to produce an analytical shock loss model that is simple enough to be described in detail while being universal and robust enough to find wide application in the fields of design and performance analysis of transonic compressors and fans. The flexible description of airfoil geometry encompasses a variety of blade shapes. Both unchoked and choked operating regimes are covered, including a precise prediction of choke occurrence. The model was validated using a number of numerical test cases.
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

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

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

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

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

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

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

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

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

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

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

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

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

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.
Numerical Investigation of Array Impingement Heat Transfer on the Target With Advanced Pin Fins
Authors: Guo Tao , Ben Yun-Peng , Liu Yu-Chao , Liu Cun-Liang , Zhu Hui-Ren
Published: September 2021

The paper proposes a technique of using advanced pin fins on a target plate to improve the impingement heat transfer performance in an array impingement cooling system. The initial shape of the advanced pin fin is a frustum of a cone. In order to enhance heat transfer and reduce flow resistance, the upper and lower sharp edges of the frustum of a cone are rounded. There are arrays of film holes on the target plate, and the influence of the crossflow is not considered. The flow and heat transfer characteristics of the array impingement flat plate and advanced pin fin plate were studied by numerical simulation. During the numerical simulation, the Reynolds number was varied from 2000 to 19500, the jet-to-plate spacing Z/d from 3 to 6 (d = 0.50mm) and the jet hole diameter d is 0.50 mm, 0.75 mm and 1.00 mm respectively. The results show that the averaged Nusselt number values for the advanced pin fin target plate showed an increase ranging from 15% to 20% over those for the flat target plate, It is generally considered that the enhancement of heat transfer is mainly due to the enhancement of fluid disturbance by the pin fins. However, by changing the size of the pin fins, it is found that the enhancement of heat transfer is mainly caused by the increase of heat transfer area, and the influence of enhancing the disturbance is not significant. The pressure loss is little higher than that of the flat plate.

The averaged Nusselt number values for the advanced pin fin target plate decreases with the increase of the jet-to-plate spacing, and increases with the increase of Reynolds number. At the same mass flow rate, the averaged heat transfer performance of the pin fin target plate decreases with the increase of jet hole diameter, and the results show that the averaged heat transfer performance of 0.5mm jet hole diameter is the best.
High-Fidelity Simulations of a High-Pressure Turbine Vane With End Walls: Impact of Secondary Structures and Spanwise Temperature Profiles on Losses
Authors: Zhao Yaomin , Sandberg Richard D.
Published: September 2021

In the present study, highly resolved large-eddy simulations of a VKI LS-89 high-pressure turbine (HPT) blade (T. Arts et al., 1990) with spanwise end-walls are performed at a Reynolds number of 0.57 million and an exit Mach number of 0.9. Two different spanwise temperature profiles, one uniform as baseline and one asymmetric profile extracted at the combustor exit from the public literature, are set at the inlet boundary. The high-fidelity data generated by the present cases are analyzed to investigate the end-wall secondary features, and show that the vortical structures that form near the leading edge of the vane include pressure-side and suction-side legs. While the end-wall vortical structures show no obvious effects on the time-averaged behavior of the pressure-side blade boundary layer, the suction-side structures induce counter rotating vortical structures and trigger rapid transition in the end-wall boundary layers. Furthermore, the cases with different inlet temperature profiles are directly compared, and the effects of the inflow on the aerothermal performance of the HPT vane are discussed. Based on the recently proposed entropy loss analysis (Zhao and Sandberg, GT2019-90126), we have been able to quantitatively show that the end-wall effects contribute significantly to the total loss of the turbine, with the main contributors being the extra viscous dissipation and turbulence production in the end-wall boundary layer.
Investigation of Unsteady Flow Characteristics in Axial Rim Seal
Authors: Xie Lei , Du Qiang , Liu Guang , Lian Zengyan , Ren Ran
Published: September 2021

Unsteady flow structures have been observed and reported in a number of recent rim-sealing investigations. These unsteady flow structures will influence the cavity pressure distribution, therefore influence the sealing efficiency. As a result, it is important to determine the mechanisms of these unsteady flow structures and how they influence the hot gas ingestion and sealing efficiency. A two-sector axial rim seal model is used to carry out the numerical investigation. The simulation is performed using the URANS method by the commercial CFD code ANSYS CFX, in which the SST turbulent model is applied. The mechanism and influence of the unsteady flow structures are analyzed. It was found that two different types of unsteadiness are observed inside the wheel space cavity: radial large flow structures dominated by the mainstream pressure distribution and inertia wave, and circumferential Kelvin-Helmholtz vortexes induced by circumferential velocity discontinuous distribution. The number and rotating speed of the radial and circumferential flow structures can be calculated using a cross-correlation method, and it was found that they can lead to a deeper ingress. By increasing the sealing flow rate, the pressure fluctuation inside the wheel space cavity is suppressed and the rotating speed of the flow structures is deaccelerated; thus, the sealing flow stabilizes the flow inside the wheel space cavity. Meanwhile, the K-H vortices’ position is lifted by the increased sealing flow rate, and the strength of the K-H vortices is suppressed, thus the sealing efficiency inside the wheel space cavity is also improved.
Experimental Investigation of Secondary Flows and Length Reduction for a Low-Pressure Compressor Transition Duct
Authors: Tsakmakidou D. , Mariah I. , Walker A. D. , Hall C. , Simpson H.
Published: September 2021

The need to reduce fuel-burn and CO2 emissions, is pushing turbofan engines towards geared architectures with very high bypass-ratios and small ultra-high-pressure ratio core engines. However, this increases the radial offset between compressor spools and leads to a more challenging design for the compressor transition ducts. To minimise weight, these ducts must achieve the radial turning in as short a length, but this leads to strong curvature induced pressure gradients, increased aerodynamic loading and likelihood of flow separation. For the duct connecting the low-pressure fan to the engine core this is further complicated by the poor-quality flow generated at the fan hub which is characterised by low total pressure and large rotating secondary flow structures.

In a previous paper the authors numerically designed modifications to an existing test facility such that the rotor would produce these large structures. The current paper presents an experimental evaluation of the new rotor design and examines the effect of the increased loss cores on the performance of a set of engine sector stators (ESS) or outlet guide vanes (OGV) and an engine representative compressor transition duct. Aerodynamic data were collected via miniature five-hole probes, for the time-averaged pressure and velocity field, and phase-locked hot-wire anemometry to capture the rotating secondary flows. Analysis of the experimental data showed that these structures promoted mixing through the ESS increasing the momentum exchange between the core and boundary layer flows. Measurements within the duct showed a continued reduction in the hub-wall boundary layer suggesting that the duct has been moved further from separation. Consequently, a more aggressive duct with 12.5% length reduction was designed and tested with the data confirming that the more aggressive duct remained fully attached. Total pressure loss data suggested a slight increase in loss over the vane row but that was offset by a reduced loss in the duct due to improved flow quality and reduced length. Overall, the 12.5% length reduction represents a significant cumulative effect in terms of reduced fuel burn and CO2 over the operational life of an engine.
Comparison of CFD Predictions of Supercritical Carbon Dioxide Axial Flow Turbines Using a Number of Turbulence Models
Authors: AbdElDayem AbdElRahman , White Martin T. , Sayma Abdulnaser I.
Published: September 2021

A detailed loss assessment of an axial turbine stage operating with a supercritical carbon dioxide (sCO2) based mixture, namely titanium tetrachloride (CO2-TiCl4 85-15%), is presented. To assess aerodynamic losses, computational fluid dynamics (CFD) simulations are conducted using a geometry generated using mean-line design equations which is part of the work delivered to the SCARABEUS project [1]. The CFD simulations are 3D steady state and employ a number of turbulence models to investigate various aerodynamic loss mechanisms. Two categories of turbulence models are used: Eddy Viscosity and Reynold’s Stress models (RSM). The Eddy Viscosity models are the k-ε, k-ε RNG, k-ω, k-ω SST and k-ω Generalized while the RSM models are BSL, LRR, w-RSM and k-ε EARSM. The comparison between different turbulence models showed minor deviations in mass-flow rate, power output and blade loading while significant deviations appear in the loss coefficients and the degree of reaction. It is noted that the k-ε model gives the highest loss coefficients and the lowest isentropic efficiencies while most of the RSM models indicate higher efficiencies and lower loss coefficients. At off-design conditions a sensitivity study revealed that the k-ε RNG model records the sharpest drop in the isentropic efficiency of 8.24% at low mass flowrate reaching 30% off-design. The efficiency sensitivity is found to be less for the other tested models getting 3.1% drop in efficiency for the LRR RSM model.
Experimental and Numerical Study on Impingement Heat Transfer and Flow Characteristics on a Semicircular Ribbed Target Surface
Authors: Kang Wang-Hao-Tai , Zhu Hui-Ren
Published: September 2021

Impact cooling is an effective way to enhance heat transfer, especially in the gas turbine blades. In the leading edge of the blade where has the high heat load, jet impingement cooling is widely used due to its high heat transfer characteristic in stagnation region. The focus is on finding a cooling structure that can improve the heat transfer effect of the internal impact structure at the leading edge without increasing the internal flow resistance. In this paper, using transient liquid crystal experiments researches for the flow and heat transfer characteristics of a semi-circular structure, which is simplified from the real blade leading edge ’s inside surface and have different rib structures. This paper studies five cases:no rib, round-shaped raised structure, oblique rib, round-shaped raised structure and oblique rib and span-wise rib and arc rib to find their heat transfer and flow characteristics. Some rib-shaped protrusion has three heights, which are 30%, 50%, 70% of the impact distance H. Experimental conditions of Reynolds number are Re = 10000, 15000, 20000, 25000, 30000. The experimental verification results show that the internally strengthened heat transfer structures studied in this paper can improve the heat transfer effect of the leading edge array of the turbine blade impact target surface without increasing the flow resistance. The structure with both oblique ribs and round-shaped raised structures has the highest surface average Nusselt number of the target plate and the lowest discharge coefficient of the channel. The structure with both span-wise ribs and arc ribs has a staggered high heat transfer area distribution, which can maybe use in some special cases.
Sensitivity Analysis of an Aircraft Engine Model Under Consideration of Dependent Variables
Authors: Salomon Julian , Göing Jan , Lück Sebastian , Broggi Matteo , Friedrichs Jens , Beer Michael
Published: September 2021

In this work the impact of combined module variances on the overall performance of a high-bypass aircraft engine is investigated. Therefore, a comprehensive sensitivity analysis on the example of a turbofan engine performance model is provided by means of Kucherenko indices. Direct influences of selected model inputs on key model outputs as well as influences due to interaction effects between these input variables are identified. The selected input variables of the performance model are partly subject to considerable dependencies that are taken into account by the Kucherenko indices.

The results confirm known direct influences of deterioration effects on the key performance parameters of the aircraft engine on the one hand, and provide profound insights into complex interaction effects between the components and their impact on the V2500-A1 aircraft engine performance on the other.
Assessment of Geometric Nonlinearities Influence on NASA Rotor 37 Response to Blade Tip/Casing Rubbing Events
Authors: Delhez Elise , Nyssen Florence , Golinval Jean-Claude , Batailly Alain
Published: September 2021

This paper uses a recently derived reduction procedure to study the contact interactions of an industrial blade undergoing large displacements. The reduction technique consists in projecting the dynamical problem onto a reduction basis composed of Craig-Bampton modes and a selection of their modal derivatives. The internal nonlinear forces due to large displacements are evaluated with the stiffness evaluation procedure and contact is numerically handled using Lagrange multipliers. The numerical strategy is applied on an open industrial compressor blade model based on the NASA rotor 37 blade in order to promote re-producibility of results. Two contact scenarios are investigated: one with direct contact between the blade and the casing and one with an abradable material deposited on the casing. The influence of geometric nonlinearities is assessed in both cases. In particular, contact interaction maps and abradable coating wear pattern maps are used to identify the main interactions that can be detrimental for the engine integrity.
Data Fusion: A Project Update & Pathway Forward
Authors: Della Villa Salvatore , Steele Robert , Shin Dongwon , Lee Sangkeun (Matt) , Johnston Travis , Liu Yong , Wen Youhai , Alman David , Perullo Christopher
Published: September 2021

At the Turbo Expo 2018: Turbomachinery Conference & Expedition, in Oslo, Norway, an innovative approach for assessing operating and near real-time data from power generating assets with meaningful predictive analytics was presented and discussed. GT2018-75030, entitled; Energy Innovation: A Focus on Power Generation Data Capture & Analytics in a Competitive Market established a challenging objective for the industry:

“To advance the notion that the fusion of total plant data, from three primary sources, with the ability to transform, analyze, and act based on integrating subject matter expertise is essential for effectively managing assets for optimum performance and profitability; executing and delivering on the promise of “Big Data” and advanced analytics.”

Throughout 2019 and 2020, a team comprised of members from Strategic Power Systems, Inc. ® (SPS), Turbine Logic (TL), and two National Labs; National Energy Technology Laboratory (NETL) and Oak Ridge National Laboratory (ORNL), collaborated on the paper’s hypothesis. The team worked with the support of funding from DOE’s Fossil Energy Program through its HPC4 Materials Program, which provided access to the High-Performance Computing assets at both laboratories. The team brought unique skills, strengths, and capabilities that would serve as the basis for an effective, open, and challenging collaboration. The engineering and data science disciplines that converged on this project provided the back-bone for the unbiased analysis and model building that took place; relying on a unique and up-to-date source of plant operating and design data essential for performing the engineering scope of work. A key objective was to use the data and the modeling to be predictive; to characterize remaining life, expended life, and to determine the “next failure” for critical systems and components.

Proof-of-concepts were tested for longer term, data-driven reliability prediction for fleets of power generating assets, near real-time prediction of power plant faults which could lead to imminent failure, and physics-based model prediction of life consumption of critical parts. Each of these pilot scale projects is summarized with key results presented.
Multi-Objective Optimization of Aero Engine Combustor Adopting an Integrated Procedure for Aero-Thermal Preliminary Design
Authors: Elmi Carlo Alberto , Vitale Ignazio , Reese Hauke , Andreini Antonio
Published: September 2021

The preliminary design of an aero-engine combustor is a multidisciplinary process that involves an extensive and systematic analysis of the design space. Simulation-driven approaches, in which several design configurations are numerically analyzed, may lead to heterogeneous models interacting with each other, sharing miscellaneous information within the process. Iterative and user-defined approaches, moreover, are inefficient when multiple and conflicting requirements are in place. To rely on integrated design methodologies has been demonstrated to be beneficial, especially if adopted in a structured approach to design optimization.

In this paper, the application of the Combustor Design System Integration (DSI) to the definition of an optimal combustor preliminary configuration will be presented. Given a combustor baseline design, the multi-objective optimization problem has been defined by targeting an optimal distribution for temperature profiles and patterns at the combustor’s exit. Dilution port characteristics, such as hole number and dimension as well as the axial position of the row have been selected as design variables. To guarantee a water-tight design process while minimizing the user effort, the DSI tools were included in a dedicated framework for driving the optimization tasks. Here, a proper CFD domain for RANS, constituted by the flame tube region extended to the dilution port feeds, was adopted for imposing the air split designed for the combustor. Concerning a “complete” combustor sector, this allows a reduction in the computational effort while still being representative for its aero-thermal behavior. The optimization task was performed using a Response Surface Method (RSM), in which multiple, specific combustor configurations were simulated and the CFD result elaborated to build a meta-model of the combustor itself. Finally, the suitability of the resulting optimized configuration has been evaluated through an “a posteriori” analysis for thermal conditions and emission levels (NOx and CO).

A lean combustion concept developed by Avio Aero with the aim of the homonymous EU research project, the NEWAC combustor, has been considered as test case.