bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Numerical Investigation of Active Flow Control Strategies for the Suppression of Aerodynamic Flow Separations in a Very Aggressive Intermediate Compressor Duct
Authors: Kaliyaperumal Ananthakrishnan , Glodic Nenad , Gutierrez Salas Mauricio , Bergh Jonathan , Fritz Stefan , Hergt Alexander 
Published: August 2024

Abstract
Due to Intermediate Compressor Ducts (ICDs) potential to reduce overall engine weight and therefore specific fuel consumption, many aerospace industry participants have embarked on programs to develop shorter and more aerodynamically “aggressive” ICD. Unfortunately, most “aggressive” designs have tended to either separate or closely approach their separation limit. As a result, in this paper, the ability of active flow control techniques (boundary layer (BL) blowing and suction) were investigated and novel schemes were designed to suppress the flow separations and thus increase the aerodynamic robustness of such ducts. The test case used in this study is a state-of-the-art, highly aggressive, ICD developed by the Institute of Propulsion Technology, German Aerospace Center (DLR), located aerodynamically close to its separation limit operating at its nominal operating point. Numerical simulations were used to characterize the aerodynamic baseline of the duct as well as the modified design. Analysis of the baseline design results confirmed the strong tendency of the flow to separate at the hub-strut corner (corner separation), mid-strut (passage separation) and in the shroud (near duct exit) regions. Boundary layer energization schemes were then explored at different streamwise locations, to identify its optimum location. The results showed that the application of a BL energization scheme (BL blowing) on the hub resulted in a positive reduction in the passage and hub-strut corner separation while the application of BL suction (at the shroud) assisted in reducing the aerodynamic separations. Finally, when both schemes were employed simultaneously, an aggregated reduction of approximately 21% in the mass-averaged total pressure loss coefficient (compared to the baseline case) was predicted.
A Comprehensive Educational App for Propulsion Systems
Authors: Tsentis Spyros , Gaitanis Aggelos , Gkoutzamanis Vasilis , Kalfas Anestis 
Published: August 2024

Abstract
This paper presents the development of a multi-platform application for rapid aeroengine performance simulation which aims to reshape conventional educational processes in aerospace propulsion taught courses. This is facilitated by enhancing students’ interaction with a broad spectrum of propulsion concepts, ranging from subsonic to hypersonic regimes. The motivation of this app draws upon the ever-increasing use of smartphone apps among the student community. It is envisaged that this phenomenon could be beneficial to widen students’ knowledge. The user of the app can rapidly extract the thermodynamic and performance parameters at different operating conditions for several propulsion concepts, including conventional turbojets and turbofans, as well as ramjets, turboramjets and advanced, pre-cooled, combined cycle engines. The development process of the application as well as the built-in models are described in detail herein. The app is employed in an aeroengine technology course in Greece and used by the students to investigate the fundamental operating principles of advanced propulsion systems. These include a turboramjet, a hydrogen-powered ramjet as well as a hybrid, pre-cooled, air-breathing rocket-cycle concept. This is facilitated through the use of the app for the performance modeling of each one of the propulsive architectures. Results show that the impact of the app on the educational process is beneficial, with the vast majority of the students providing positive feedback. It is found that the app has far increased their interest and level of knowledge related to propulsion systems, in comparison to traditional teaching techniques. This would have been impossible in the time frame of an academic semester without the implementation of the app.
Rich Ammonia Flame Shapes and No Relaxation: Facility Development and Characterization
Authors: Cole Renee , Gubbi Srujan , Wu David , Emerson Benjamin , Noble David R. , Steele Robert , Sun Wenting , Lieuwen Tim 
Published: August 2024

Abstract
Ammonia (NH3) is a carbon-free fuel and hydrogen carrier; however, the presence of fuel-bound nitrogen has the potential to produce substantial nitrous oxide (NOx) emissions. Staged combustion, starting with a rich fuel reaction/decomposition zone, has the potential for low NO levels but can also lead to very significant NO levels if not designed correctly. This staged strategy takes advantage of the fact that equilibrium NO emissions from rich NH3 combustion are quite low. However, significant NO levels are still produced in rich flames and require a specific relaxation time, which can be quite long, to drop down to equilibrium levels. Thus, a key design attribute for ammonia combustors is sufficient residence time for NO relaxation. Given an overall combustor length, the NO relaxation zone is a direct function of the rich flame length, which can be quite long. Moreover, the flame length is a strong function of the flame stabilization location, e.g., the flame length in an annular swirling flow can easily vary by a factor of two depending upon the flame stabilization location. Moreover, swirl flames exhibit very long “tornado” configurations in certain conditions. For these reasons, even under conditions where the flame is stabilized, its configuration will dramatically influence the amount of time for the NO relaxation process. This paper introduces a test rig to explore flame configurations and post-flame NO relaxation for ammonia combustion. The rig features a modular swirler, a long primary stage, and a traversing emissions probe. The paper presents images of flame configurations over a range of conditions and maps different bifurcations in flame configuration.
Heat Transfer Evaluation on Turbine Vane With Corrugated Wall Impingement Structure Using Infrared Camera
Authors: Okamine Ryunosuke , Ito Ryuta , Mizukami Satoshi , Sakata Atsuya , Hada Satoshi 
Published: August 2024

Abstract
Impingement cooling is an effective technique used to cool hot gas path parts, minimizing the amount of cooling air required, and thereby improving the performance of gas turbines. However, crossflow from spent air of upstream impingement jets disrupts downstream impingement jets resulting in decreased heat transfer performance. To reduce the influence of crossflow, prior investigators have proposed using a corrugated wall type impingement structure.
Although fundamental tests of simplified corrugated wall impingement structures have been conducted in the past to confirm the basic cooling performance, it is desirable to verify the metal temperature distribution on an actual turbine vane cooled by a corrugated wall impingement structure. This study presents results from a turbine cascade test where pressure and suction side surface temperatures of an actual vane are measured using an infrared camera. Thermocouples mounted at different locations around the vane are used to correct the IR thermal image data. Based on these measurements, it was concluded that the corrugated wall impingement structure can achieve the target cooling effectiveness for both pressure side and suction side airfoil surfaces.
Forced Response of Bladed Disks With Excitation Variability
Authors: Xiao Yue , Panning-von Scheidt Lars 
Published: August 2024

Abstract
The prediction of forced vibration of mistuned bladed disks remains an important topic in turbomachinery design. The investigation of mistuning usually focuses on the blades in terms of their different structural properties. The excitation mechanism is considered to be mainly caused e.g. by the wakes from an upstream and the potential field from a downstream blade row. In recent years, it has been demonstrated that the Tyler-Sofrin modes (scattered or spinning modes) may affect blade forcing significantly and cause variable forcing amplitudes on individual blades in multistage turbomachinery. As a result, the vibration is localized at some of the blades forced by greater amplitudes, which leads to a higher risk damage for those blades. In this paper, the generation mechanism of TSMs is demonstrated and the effect of TSMs on blade forced responses is studied. Depending on the configuration of turbomachinery, excitation arising from Tyler-Sofrin modes may consist of different frequency components, which requires multiharmonic balance method (MHBM) to find the periodic solutions in presence of nonlinear blade couplings1. The methodologies for calculating linear and nonlinear FRFs are presented here on an academic bladed disk with shroud coupling, while TSMs is taken as part of the blade excitation.
Optimization of a Steam Turbine for Mechanical Drive Applications
Authors: Neil Adam , Rao Nikhil , Smith Paul 
Published: August 2024

Abstract
Axial flow steam turbines find wide application in several industries, such as oil & gas, petrochemicals, etc. The applications are primarily as mechanical drive turbines, to drive the process compressors. Because it is not feasible to design and optimize new hardware for each specific application, mechanical drive steam turbines are rarely clean sheet designs. These designs are developed from the available hardware inventory, which imposes certain geometric restrictions on the aerodynamic design and optimization of the flow path. Ensuring the mechanical reliability of the design is also critical to the functioning of the turbine. The modifications made to improve the reliability need to be executed with minimal impact to the performance. This paper will outline several concepts that form the basis of the aero-thermodynamic and mechanical design and optimization of mechanical drive axial flow turbines.
Geometric and Flow Characterization of Additively Manufactured Turbine Blades With Drilled Film Cooling Holes
Authors: McCormack Kelsey E. , Rozman Maria , Berdanier Reid A. , Thole Karen A. 
Published: August 2024

Abstract
As designers investigate new cooling technologies to advance future gas turbine engines, manufacturing methods that are fast and accurate are needed. Additive manufacturing facilitates the rapid prototyping of parts at a cost lower than conventional casting, but is challenged in accurately reproducing small features such as turbulators, pin fins and film cooling holes. This study explores the potential application of additive manufacturing and advanced hole drill methods as tools to investigate cooling technologies for future turbine blade designs. Data from computed tomography scans are used to non-destructively evaluate each of the cooling features in the blade. The resulting flow performance of these parts is further related to the manufacturing through benchtop flow testing. Results show that while total blade flow is consistent for all additively manufactured cooled blades, flow through smaller regions of the blades shows variations. Shaped film cooling holes manufactured using a high-speed electrical discharge machining method are within tolerance in the metering section but do not expand at the specified angle in the diffuser even though design tolerances are met. In contrast to high-speed EDM, conventional EDM holes are undersized throughout the length of the hole. Due to the additive manufacturing process, the surface roughness was higher on the additively manufactured parts in the current study than has been previously reported for surface roughness of commonly used cast components. The roughness results show high levels on thin walls, particularly at the trailing edge as well as on downskin surfaces. Internal surface roughness is higher than external roughness at most locations on the blade. The results of this study confirm that additive manufacturing along with advanced hole drilling techniques offer faster development of blade cooling designs.
On the Performance of Variable-Geometry Ducted E-Fans
Authors: Kavvalos Mavroudis D. , Schnell Rainer , Mennicken Maximilian , Trost Marco , Kyprianidis Konstantinos G. 
Published: August 2024

Abstract
Electrically-driven ducted fans (e-fans), either underwing-mounted or located at the aft-fuselage, can potentially improve the system overall efficiency in hybrid-electric propulsion architectures by increasing their thrust share over the thrust generated by the main engines. However, the low design pressure ratio of such e-fans make them prone to operability issues at off-design conditions, i.e. take-off, where nozzle pressure ratio is close or below the critical value. This paper investigates the operational limitations of such e-fans, proving the necessity of variable geometry. A component zooming approach is deployed by integrating a streamline curvature method within an aero-engine performance tool to investigate the e-fan installed performance and operability. The concepts of variable pitch fan (VPF) and variable area nozzle (VAN) are systematically explored to quantify any performance benefits, while the unavoidable added-weight challenges due to variable geometry are taken into account. Although e-fans with low design pressure ratio (PR) are more susceptible to operability issues compared to higher PR e-fans, the former show improved overall efficiency levels, mainly dominated by propulsive efficiency. It is found that variable geometry not only tackles operability but it can improve the off-design overall efficiency of e-fans even more. VPF mostly affects the component efficiency by reshaping the e-fan performance maps, while VAN has a greater impact on propulsive efficiency by moving the operating points.
Impact of Various Intake Configurations on the Flight Mission Performance of an Unmanned Aircraft
Authors: Remiger Jonas , Grois Andreas , Stößel Marcel , Kožulović Dragan , Krummenauer Michael 
Published: August 2024

Abstract
Well-defined intake-engine interfaces are of great importance in the aircraft design process. The focus of this paper is on various coefficients for data transfer at the aerodynamic interface plane (AIP) as a critical interface between the engine and the aircraft. To evaluate these coefficients, different intake geometries are modeled and simulated. The objective of the study is to provide a holistic view of the interactions between flight conditions, aircraft, intake systems and their effects on engine performance using previously generated computational fluid dynamics (CFD) results which are further used in the engine mission simulation system (EMSS). The effects of intake distortion on compressor behavior and engine performance are investigated using the parallel compressor model. All results of the investigation are obtained via the time-resolved simulation of an exemplary flight mission. The results first discuss the influence of flight conditions on the total pressure loss of each inlet and the corresponding behavior of the investigated distortion parameters. It is shown that not only the inlet geometry but also the coefficient used to represent the distortions in the performance calculation has an influence on the mission performance. Finally, it is shown that depending on the coefficient used to map the inlet distortion, there is a clear difference in the operating behavior of the compressor. The proposed γ coefficient predicts a critical approach to the surge margin. The DC60 would still suggest a safe operation of the compressor.
Large Eddy Simulation of an Open Fan Blade at Full-Scale Reynolds Number
Authors: Priebe Stephan , Jourdan Eduardo , Mousavi Arash , Karve Ravish , Chakrabarti Suryapratim , D’Aquila Luke , Yi Junsok , Alhawwary Mohammad , Bharadwaj Ananthan Varun , Ramakrishnan Kishore , Wood Trevor 
Published: August 2024

Abstract
Large-scale commercial turbofan designs are typically evaluated early in the technology maturation phase through subscale rig tests, while evaluations at full scale can only feasibly occur much later in a given engine development program. Therefore, how Reynolds number (Re) affects the aerodynamic and acoustic performance is of key interest while multiple candidate fan designs are still being evaluated and refined early in the program, and often tested scaled down to lower Re relative to the end application. To confidently evaluate full-scale Re performance however, large-scale physical testing is traditionally required because the high-fidelity simulations needed to capture the complex physics associated with high Re turbulent flows, such as wall-resolved Large Eddy Simulations (LES), are challenging due to the extremely high computational cost. In this paper, we present wall-resolved LES of an open fan blade at full scale for a highly loaded design operating at a condition representative of takeoff for acoustic considerations. The simulations are at high order (up to sixth) and have been performed using the unstructured LES solver, GENESIS. These simulations extend prior research to allow for a study of practically relevant flight scale Re, for which wall-resolved LES is now possible with computing capability available at the Oak Ridge Leadership Computing Facility (OLCF) exascale supercomputer, Frontier. The observed effects at flight scale Reynolds number of the flow physics on the blade and into the wake are presented in specific regions of interest that can affect the overall blade aeroacoustic design.
Nonlinear Normal Modes-Related Isolated Branches of Subharmonic Solutions for Forced Response Blade-Tip/Casing Contact Problems
Authors: Vadcard Thibaut , Thouverez Fabrice , Batailly Alain 
Published: August 2024

Abstract
This article investigates the emergence of isolated branches of solutions for blade-tip/casing structural contact configurations by means of a numerical procedure relying on Melnikov’s energy principle. This study is carried out on the open fan blade model NASA rotor 67 in order to promote the reproducibility of the results. The blade is subjected to an harmonic forcing so as to initiate rubbing interactions. Contact is modeled in the frequency domain by the dynamic Lagrangian frequency-time harmonic balance method (DLFT-HBM) that accounts for vibro-impact as well as dry friction. This paper employs an isola detection procedure that was shown to give accurate results on such highly nonlinear applications [1]. Several types of harmonic forcing are applied to the blade in order to observe subharmonic (i.e. with a fundamental frequency expressed as a fraction of the excitation frequency) isolated solutions. The existence of these solutions is shown to be related to nonlinear normal modes that feature lower periodicities than the excitation. The periodicity of the solutions is assumed to be linked to the periodicity of the nonlinear normal modes from which these solutions emerge. In some configurations, it is shown that nonlinear periodic solutions exist in the form of isolated branches while the main predicted response remains within the linear domain. This behavior is particularly detrimental since numerical strategies tackling nonlinear problems are usually not put to use when the response of the system is expected to be linear. The existence of such solutions is cross-checked by means of reference time integration simulations. Finally, an excitation of random shape is applied to show that this complex phenomenon persists for non-simplified excitation shapes.
Techno-Economic Analysis and Optimal sCO2 Power Cycle Configuration for Novel CSP Plants Adopting Tubular Fluidized Particles Central Receivers
Authors: Alfani Dario , Sobic Filip , Astolfi Marco , Binotti Marco , Silva Paolo 
Published: August 2024

Abstract
Concentrating Solar Power (CSP) plants, thanks to the use of cost-competitive Thermal Energy Storage (TES), can provide back-up power guaranteeing a zero-emission alternative to conventional power plants and offer of balancing services on the electrical grid. Current state-of-the-art solar tower plants are based on conventional steam Rankine cycles and adopt solar salts both as heat transfer and storage fluid in a direct 2-tanks TES system. However, the 2022 average CSP levelized cost of electricity, equal to 0.118 $/kWh, is still remarkably higher than other renewable technologies. Next generation CSP solar towers are expected to employ novel high-temperature receivers able to reach temperatures above 700°C, leading to improved efficiency of the power block and thus to more competitive technoeconomic performances. In this context, the Horizon Europe Powder2Power project aims at demonstrating at the MW-scale the operation of an innovative tubular solar receiver adopting fluidized particles that will allow to reach temperature as high as 750°C while ensuring intra-week storage capacities at reduced cost, thereby increasing the flexibility and the competitiveness of CSP generation and its value for the grid.
For such a high temperature and high flexibility application, the adoption of sCO2 Brayton cycles as power conversion systems is the most recommended option thanks to their high efficiency, compactness of turbomachinery, simple plant arrangement, no water consumption, and fast transients in operation. This work aims to confirm the potential advantages of this power block technology for next generation CSP plants based on tubular fluidized particles solar receivers. A MATLAB+REFPROP V10 numerical model is developed to calculate the system overall efficiency and the capital cost for different cycle configurations, and it is employed to identify the optimal techno-economic solutions which can minimize the specific cost of the overall CSP plant. The model implements ad-hoc routines for the component sizing and uses referenced cost correlations for each component of the power block (compressor, heat rejection unit, recuperators, and turbine) and of the solar field (heliostat, tower, and receiver).
Results allow selecting the optimal sCO2 power cycle configuration and nominal design parameters, also considering the tradeoff on the solar-to-electricity efficiency and the total investment cost of the system.
Effect of Piston Ring Grooves on the Radial and Tangential Forces of a Squeeze Film Damper
Authors: Giampaolo Emanuele , Arghir Mihai , Festjens Hugo 
Published: August 2024

Abstract
Squeeze film dampers (SFDs) are components of rotating machinery used to reduce vibration amplitudes and improve the rotor dynamic stability. Piston rings (PRs) are often employed as end seals for SFDs. They enhance the damping forces while remaining limited to a small axial length. Piston rings are installed in grooves whose dimensions (width and depth) are generally one order of magnitude larger than the radial clearance of the SFD. The radial and axial clearances after the PR is mounted may impact the forces generated by the SFD to the point that they have to be considered as design parameters. CFD and bulk flow (BF) approaches were used to determine the impact of the axial and radial clearances introduced by the presence of the PRs. CFD is an accurate, direct approach to the problem but it requires intensive computational resources. Therefore, BF-based methods are considered as an appropriate option for a wide range of SFD operating conditions. The BF approach developed previously is now extended to include the PR clearances. The results are validated using CFD simulations for a simplified SFD geometry. This comparison underlines the strengths and limits of the BF approach. The impact of the PR clearances on the radial and tangential forces is then evaluated on a realistic SFD by using the BF model. A parametric study is conducted to explore the impact of varying the axial and radial PR clearances. Overall, a procedure for correctly considering PR clearances in a BF framework is proposed and validated, while complementary elements for understanding the role of PR clearances are described.