bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Atomization Characteristics on Lean Blow-Out Limits in a Gas Turbine Combustor
Authors: Wang Xiwei , Huang Yong , Sun Lei , Liu Yunfeng , Wang Donghui 
Published: September 2021

Abstract
In order to investigate the effects of atomization characteristics on the lean blow-out (LBO) performance, an experimental study was carried out on the spray and the combustion. The LBO limits and the outlet temperature near the LBO condition of different atomizers were measured in a single dome rectangular model combustor with a dual-radial and a dual-axial swirl cup, respectively. In the combustor, the spray analysis was performed on different atomizers (without combustion) at the LBO condition. The Malvern particle size analyzer was used to measure the Sauter Mean Diameter (SMD), and the laser sheet was used to take spray images. First of all, the spray pattern determines the minimum heat release required to maintain the combustion, which corresponds to the ideal LBO fuel/air ratio (FAR), which is the maximum potential for the lean combustion. Secondly, the matching of the spray SMD, the droplet size spatial distribution and the droplet initial velocity with the flow field determines the ratio of the completely burned fuel to the total fuel ejected from the atomizer, which determines the extent to which the combustor exerts its lean combustion potential. In addition, the numerical simulation of the flow field of the combustor with two structures was carried out, which provided an important basis for the theoretical analysis of this paper.
Design and Evaluation of a Flow Capturing Device for a High-Speed Wind Tunnel
Authors: Graiff Mattia , Staggl Marian , Göttlich Emil , Wakelam Christian 
Published: September 2021

Abstract
Wind tunnel testing belongs to the most significant aspects of the technical development process. In order to improve the test environment conditions and open the possibility of closed loop operation, a flow capturing device is developed for a highspeed wind tunnel previously exhausting to ambient. The highspeed wind tunnel is used in conjunction with annular sector cascade test rigs to evaluate the performance of intermediate turbine ducts. In the presented paper, a modular design approach for the flow capturing device is presented; particular attention is reserved to optimal integration within the pre-existing test environment and to an efficient sealing strategy. Computational results provide the basis for the correct sizing of the device; the aerodynamic effects induced by the flow capturing device downstream of an annular sector cascade rig are shown to bear no influence on the quality of the test data. The presented results of several tests conducted under a wide range of conditions confirm the viability of the developed flow capturing device. The improvements to the pre-existing experimental setup achieved with the addition of the flow capturing device are furthermore presented in this paper, focusing on the obtained reduction in sound pressure and temperature level within the test facilities.
Effects of Surface Waviness on Fan Blade Boundary Layer Transition and Profile Loss — Part II: Experimental Assessments and Applications
Authors: Lee Jinwook , Ramaswamy Vaishnavi , Spakovszky Zoltán S. , Greitzer Edward M. , Drela Mark , Talbotec Jérôme 
Published: September 2021

Abstract
Part II describes the experimental assessment and the application of the ideas in Part I concerning the mechanisms that determine the role of blade surface waviness on laminar-turbulent transition and their consequent effect on civil aircraft fan performance. A natural transition wind tunnel was designed and constructed to characterize the impact of surface waviness on transition, using both hotwire anemometry and infrared thermography. The experimental results support the new hypothesis presented in Part I, concerning the way in which blade surface waviness affects fan performance through motion of the transition onset location due to interaction between surface waviness and Tollmien-Schlichting (TS) boundary layer instability. In particular, the theoretical amplification of the TS waves, and the corresponding transition onset location movement due to surface waviness, was borne out over a range of variations in Reynolds number, non-dimensional surface wavelength, non-dimensional surface wave height, and location of surface wave initiation, relevant to composite fan blade parameters. Further, the increase of receptivity coefficient, and thus the initial amplitude of disturbances due to geometric resonance between surface wavelength and TS wavelength, was also confirmed by the experiments. Surface waviness was estimated, in some cases, to result in a nearly 1% decrease in fan efficiency compared to a non-wavy blade. Suggestions are given for mitigation of the effects of waviness, including the idea of blade curvature rescheduling as a method to delay transition and thus decrease loss.
Mechanical and Thermal Deformation Analysis of a Large Polymer Lined Tilting Pad Journal Bearing
Authors: Stottrop Michael , Bender Beate 
Published: September 2021

Abstract
An increase of specific load in large tilting pad journal bearings (TPJB) leads to major mechanically and thermally induced deformation of the pads and limits the load carrying capacity. In this paper, we present a theoretical approach to determine deformation of a TPJB with PEEK (Polyetheretherketone) polymer lined pads by means of a thermo-elasto-hydrodynamic model. The objective of this investigation is a quantitative analysis of the deformation characteristics of a five-pad TPJB with a nominal diameter of 500 mm. Mechanical and thermal deformations are simulated for both the steel backing and the polymer lining. The deformation characteristics calculated with the numerical model are compared to simulation results of an experimentally validated model with a white-metal lining.
The results indicate an improvement in bearing characteristics with the PEEK lining, as maximum pressure decreases and minimum film thickness increases. Due to the insulating properties of the PEEK layer, thermally induced pad deformation is reduced significantly.
Flow Physics in a Large Rotor Tip Gap in a Multi-Stage Axial Compressor
Authors: Hah Chunill 
Published: September 2021

Abstract
The flow physics in a large rotor tip gap in a 1.5-stage axial compressor is investigated in the current study. The flow structure in the rotor tip region is complex with several dominant vortical structures of opposite rotation, resulting in inhomogeneous and highly anisotropic turbulence. Earlier measurements show that eddy viscosity is negative over large parts of the tip region and eddy viscosity varies among stress/strain components. The present study aims to understand how the complex nature of rotor tip leakage flow affects compressor performance when the tip gap size is greater than 4–5% of the rotor span, which is typical of advanced small core engines. Unsteady Reynolds-averaged Navier-Stokes (URANS) and Large Eddy Simulation (LES) techniques are applied to study flow physics in a large rotor tip gap (5.5% of rotor span) in a 1.5-stage axial compressor. Calculated flow fields from the two different approaches are compared with available measurements and examined in detail. LES calculates the pressure rise in the present compressor fairly well, while URANS with a standard two-equation turbulence closure underpredicts the pressure rise by 15–20% of the measured values. The current study shows that URANS with the current turbulence closure produces much higher all-positive eddy viscosity in the tip-gap region compared to measurements and LES. The distribution of eddy viscosity in the URANS simulation is also wrong. Consequently, the flow in the tip region is highly damped with significantly larger blockage generation, which results in the tip leakage vortex (TLV) staying closer to the blade suction side compared to the measurement. When the TLV stays closer to the blade, both flow turning and the pressure rise across the compressor are reduced compared to the measurements. It appears that this effect is amplified by a large rotor tip gap.
Numerical Investigation on the Influence of Tip Shroud Design Characteristics on the Aerodynamic Damping of a Last Stage Blade
Authors: Rozendaal Alexander V. , Torkaman Alex , Fiebiger Stephen W. 
Published: September 2021

Abstract
The accurate predication of aerodynamic flutter margin continues to be an area of growing importance in the design of rotating turbomachinery, especially when considering the ongoing industry objectives for increased operating efficiency, higher power output, and reduced fuel consumption. Improvements in these areas are commonly achieved through incremental design changes to existing hardware, and often trend with higher pressure ratios and mass flow rates through the machine. In many cases, the extent of these flow improvements become constrained by the stability margins of flutter-limiting components such as front-stage compressor blades and last stage turbine blades. In such cases, designers are left with the difficult task of mitigating the flutter risk, but without limiting the overall performance of the machine.
The tip shroud of a typical last stage turbine blade can significantly influence the flutter response of the blade. It is this reason that underlines the importance for understanding the sensitivity of shroud design parameters when attempting to achieve a flutter-free design, especially if the aerodynamic qualities of the airfoil need to be preserved. This paper evaluates the flutter performance of a last stage industrial gas turbine blade with multiple tip shroud configurations and demonstrates the influence of the selected design parameters with respect to the aerodynamic damping characteristics of the blade.
Energy Dissipation Metrics for Fatigue Damage Detection in the Short Crack Regime for Aluminum Alloys
Authors: Dharmadhikari Susheel , Basak Amrita 
Published: September 2021

Abstract
In this paper, three distinct energy dissipation metrics are proposed to enable fatigue damage detection in aluminum specimens. The metrics are (i) Energy Dissipation Rate, (ii) Cumulative Energy Dissipation, and (iii) Material Stiffness. They are created by using the force and displacement signals obtained from the fatigue testing apparatus during the testing of Al7075-T6 specimens. The apparatus is also equipped with a confocal microscope which calibrates the fatigue damage detection at a crack thickness of 10 μm, thereby, enabling precise detection in the short crack regime. Using all the three metrics, optimal thresholds are computed using receiver operating characteristics and the average accuracy of damage detection in quantified. Accordingly, the three metrics show an accuracy of 84.06%, 100%, and 84.32%, respectively in detecting the cracked specimens.
3D Printing of Ceramic Shell Molds for Precision Casting of Turbine Blades
Authors: Magerramova Liubov , Kozlov Boris , Kratt Eugene 
Published: September 2021

Abstract
Traditionally, the technology used in the production of gas turbine blade castings characterized by a large number of technological conversions, high labor costs with a large amount of manual labor and the need to produce various types of complex and expensive equipment at different stages of production. This work aims to reduce the time and money spent on the manufacturing of ceramic shell shapes — a form suitable for the standard methods of precision casting by traditional heat-resistant nickel alloys. The proposed approached involves obtaining a shell shape with an internal core as a single, non-assembled product, without lengthy and time-consuming design and manufacturing processes involved in forming equipment for the production of castings based on smelted models. The proposed method is based on the use of 3D printing with refractory ceramic pastes.
Using both uncooled and cooled blades as examples, models of casting molds were designed, technological processes were developed, and ceramic shell molds were manufactured.
Experimental casting into a manufactured ceramic shell mold for an uncooled blade with a bandage shelf was performed and showed satisfactory results.
Design and Development of a New Rotating Turbine Research Facility For Investigating the Interaction Between Mainstream and Various Secondary Air at Relevant Engine Conditions
Authors: Okita Yoji , Futamura Hisao , Yamane Takashi , Suzuki Masaya , Tanaka Nozomi , Tanimitsu Haruyuki , Iguchi Junichi 
Published: September 2021

Abstract
This paper reports a new turbine research facility that was recently completed in Japan Aerospace Exploration Agency (JAXA). The facility is a full annular rotating transonic turbine rig that allows a continuous operation of scaled and/or full-scale axial HPT or LPT.
The rig design was especially focused on the ability of simulating the aerodynamic and thermal interaction between main gas paths and various / massive secondary air flows at conditions of dominant aero-heat parameters well matched to those of modern aero-engines. Cooling air can be delivered to the airfoils of vanes/blades and the endwalls separately at a massflow range covering the typical conditions. Rotor forward and aft purge air as well as through-casing cooling air can be injected with each flowrate independently controlled.
The facility, which has significant capabilities with several large compressors of 10MW in total, 5MW mainflow heater, 6MW drive motor/generator, etc., can be applied to a very wide range of turbine designs.
A series of shakedown testing has been carried out since the completion of construction in 2019. The commissioning phase of the rig will complete in early 2021 and then the rig will enter service. The very first test with a scaled HPT is planned to start in the last quarter of 2021.
Insight on Aerodynamic Damping of the Civil Transonic Fan Blade
Authors: Lian Bo , Hu Ping , Chen Yong , Zhu Xiaocheng , Du Zhaohui 
Published: September 2021

Abstract
Flutter seriously affects the safety and reliability of aeroengine. In this paper, influence coefficient method (ICM) and traveling wave method (TWM) are used to calculate the aerodynamic damping of transonic fan blades of civil aviation engine at different nodal diameters (NDs) and structural modes. The results of two methods are basically consistent but the ICM only needs to simulate seven passages for all of the NDs, which has higher computation efficiency. The results show that under the design condition, the first three structural modes of the blade are aero-elastic stable for each ND, and the aerodynamic damping gets the minimum at ND1 for the first bending mode. As the back pressure deviates from design condition towards choking or stall, the aerodynamic damping obviously decrease and even negative aerodynamic damping occurs at normalized mass flow rate of 0.950. Dynamic mode decomposition (DMD) is applied to analyze the transient pressure on vibrating blade surface. Dominant flow structures like shock wave oscillating and corresponding frequency on blade surface can be acquired through DMD method. TWM simulation with DMD analysis indicates that the shock wave changes the phase of the pressure in the region next to downstream of the shock wave, which makes the aerodynamic work concentrate locally.
On the Challenge of Determining the Surge Limit of Turbocharger Compressors: Part 2 – Capabilities of a Geometrically Reduced Numerical Model
Authors: Paul Dominik , Ratz Johannes , Eißler Werner 
Published: September 2021

Abstract
Steady-state numerical simulations are an essential instrument in the design process of centrifugal compressors for automotive turbochargers in an industrial environment. Although this method is state-of-the-art, the natural unsteadiness of the compressor flow especially close to stall and surge is suppressed by this kind of simulation.
Unsteady numerical simulations of the complete compressor geometry are necessary to detect unstable flow structures leading to surge. As numerical costs and thus the time needed for unsteady simulations correlate with the size of numerical setup, it is not possible for industrial applications to investigate an unsteady operation condition of a centrifugal compressor. On account of that fact, it would be beneficial to reduce the model and include only the most decisive components which are responsible for the significant flow phenomena within the impeller leading to surge.
The objective of this research paper is the investigation of the CFD simulation capabilities of a reduced radial compressor model for steady-state operation conditions using as a robust basis for further transient analysis. Thus, the results of a reduced model setup of one blade segment are compared to a full model setup.
It is concluded that the segment model approach is capable of investigating flow phenomena within the impeller without neglecting fundamental flow structures. In addition, the consequences of the geometric reduction to a diffuser segment without volute on different flow variables are studied. This provides the guidance for further transient studies.
The complete model setup, in conjunction with its validation by experimental data, serves as the starting point for this research paper. Dielenschneider et al.[1] present in the first part of the paper the procedure and a detailed comparison of complete model results with experimental analysis.
A Probabilistic Machine Learning Framework for Explicit Inverse Design of Industrial Gas Turbine Blades
Authors: Ghosh Sayan , Andreoli Valeria , Padmanabha Govinda A. , Peng Cheng , Atkinson Steven , Pandita Piyush , Vandeputte Thomas , Zabaras Nicholas , Wang Liping 
Published: September 2021

Abstract
One of the critical components in Industrial Gas Turbines (IGT) is the turbine blade. Design of turbine blades needs to consider multiple aspects like aerodynamic efficiency, durability, safety and manufacturing, which make the design process sequential and iterative. The sequential nature of these iterations forces a long design cycle time, ranging from a several months to years. Due to the reactionary nature of these iterations, little effort has been made to accumulate data in a manner that allows for deep exploration and understanding of the total design space. This is exemplified in the process of designing the individual components of the IGT resulting in a potential unrealized efficiency. To overcome the aforementioned challenges, we demonstrate a probabilistic inverse design machine learning framework, namely Pro-ML IDeAS, to carry out an explicit inverse design. Pro-ML IDeAS calculates the design explicitly without costly iteration and overcomes the challenges associated with ill-posed inverse problems. In this work the framework will be demonstrated on inverse aerodynamic design of 2D airfoil of turbine blades.
Performance Testing of L-PBF Produced Honeycombs Out of IN625
Authors: Heitmann Timo , Geisen Ole , Hühn Lisa , Munz Oliver , Bardenhagen Andreas 
Published: September 2021

Abstract
Laser Powder Bed Fusion (L-PBF) enables the production of complex metallic parts. Processes using pulsed wave (PW) laser radiation have been proven to be well suited to build thin-walled honeycomb structures. However, the behavior of these structures under load conditions remains mostly unexplored. The objective of this paper is to characterize L-PBF produced honeycombs by investigating their rub and leakage performance. A pulse modulated process based on previous studies is optimized for productivity and used to build L-PBF test samples out of Inconel 625 (IN625). The honeycomb cell geometry is adjusted for improved printability of the overhanging walls. Repeatable L-PBF production of honeycombs with a wall thickness of about 100 μm is confirmed. Conventionally manufactured honeycomb samples out of sheet metal are tested as reference. The rub experiments cover radial incursion rates of up to 0.5 mm/s and relative velocities of up to 165 ms−1 at incursion depths (ID) between 0.5 and 2.0 mm. Lower incursion forces are observed for the L-PBF components, with a higher degree of abrasion. The leakage tests examine the mass flow rate for pressure ratios between 1.05 and 2.0 at constant gap size and constant back pressure. The L-PBF honeycomb seals show a higher mass flow rate, with the slightly larger cell size and higher surface roughness appearing to be the main influencing factors. Overall, improved rubbing behavior and 10 % higher leakage than the conventional probes demonstrate the applicability of L-PBF for honeycomb sealing systems. Future performance improvements through dedicated L-PBF designs can be expected.
Influence of Acoustically Excited Airflows on a Planar Airblast Prefilmer
Authors: Christou Thomas , Stelzner Björn , Zarzalis Nikolaos 
Published: September 2021

Abstract
In order to meet the higher requirements for clean combustion technology in aircraft engine applications and thus reduce harmful emissions, especially nitrogen oxide emissions, the major jet engine manufacturers are developing lean premixed prevaporized (LPP) combustors that operate at very high pressure. In this context, thermoacoustic instabilities may occur within the combustion chamber. The unsteady heat released by the flame generates pressure waves, which are coupled to the inlet air velocity by a feedback loop. This loop amplifies the instabilities of the inlet air velocity, which in turn influences the atomization process.
Since the atomization process at the airblast atomizers of most jet engine combustors determines critical operating characteristics such as air-to-fuel ratio (AFR), flame stability, or NOx emissions, predicting the performance of this process under unsteady conditions has a significant value.
The present experimental study focuses on the influence of oscillating airflows on the spray characteristics at the airblast atomization process. The experimental setup was based on a two-dimensional prefilmer where a water film flow was introduced on one surface. The airflow was excited by a siren, whereby an excitation frequency near 94 Hz was investigated. The airflow oscillation under this excitation frequency was characterized using a Constant Temperature Anemometer (CTA), while the generated spray was investigated with a Phase Doppler Anemometry (PDA) system.
The spray was investigated in a variety of positions along the radial axis, providing spatial information, apart from temporal. The characterization of the spray via PDA includes a two-component droplet velocity detection and diameter measurement, while the spray mass flux for each measured position was also calculated. The acquired data were phase averaged via an in-house developed processing algorithm, while through a statistical analysis the confidence intervals of the calculations were included. The excitation frequency strongly influenced all spray characteristics, namely, the Sauter Mean Diameter (SMD), the droplet velocities, the mass flux, as well as the local air-to-liquid ratio (ALR). Depending on the phase angle, the size distribution of the spray changes, explaining the observed oscillating behavior of the spray characteristics.