bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impact of the Wall-Parallel Length Scale of Roughness on the Development of Turbulent Boundary Layers in Turbines
Authors: Berhane Abigail M. , Longley John P. 
Published: August 2024

Abstract
The detrimental effects of surface roughness on the growth of turbulent boundary layers in turbines, and compressors, are well known. However, robust prediction of these effects can be problematic, especially for surfaces which are not similar to sand grains. Several publications have proposed that additional parameters such as slope, skew, etc. can be used to augment a wall-normal measure such as Sa to correlate surface roughness. Here, we introduce a new roughness parameter, the mean separation, which explicitly measures the average separation between each local minima and its closest local maxima. Scans of turbine blade surfaces showed that they can have mean separations which are up to six times that of the sand grain surface which has the same wall-normal length scale.
The availability of high resolution, typically &lt; 0.1 μm, area scanning tools and 3-D printing techniques have enabled the development of a “Scan-Scale-Print-Measure” methodology. A surface scan is scaled-up, 3-D printed, applied to a flat-plate and then the turbulent boundary layer is measured. The surface roughness-loss is the additional momentum thickness, above that of the datum smooth surface.
The Scan-Scale-Print-Measure methodology has enabled parametric studies to be undertaken where the mean separation was increased whilst keeping either the Sa value or the feature size constant. Both studies demonstrated a surface roughness-loss that was strongly dependent on the mean separation and different to a Schlichting based sand grain correlation. It also showed that for large mean separations the roughness-loss decreased to zero. A parametric study into pits-and-peaks surface features showed that, at the same wall-normal length scale, peaks generated a surface roughness-loss twice that of pits.
An engine representative surface produced only half the roughness-loss that would be attributed to a sand grain surface. The measured surface roughness-loss could be estimated within 5% using the aforementioned parametric studies.
Status of Gas Turbine Performance Degradation
Authors: Kurz Rainer , Brun Klaus , Pinelli Michele , Suman Alessio 
Published: August 2024

Abstract
Any prime mover exhibits the effects of wear and fouling over time. The degradation affects the performance of such a machine. For a industrial gas turbine, the problem includes predicting the effects of wear and fouling on the performance of such an engine, as well as the description and determination of the mechanisms that cause wear and in particular fouling. The degradation effects can be classified in several categories, for example recoverable vs. non-recoverable degradation, alluding to the fact that cleaning the engine is possible for some types of degradation. Another differentiation is fouling, where fine particles adhere to blade surfaces as opposed to material removal from heavier particles or rubbing. The systematic attempts to determine degradation mechanisms, their impact on gas turbine performance, and mitigation methods go back several decades. More recently, simulation methods have closed the gap between observed contamination and numerical results. The deterioration of gas turbine components, such as the compressor or turbine sections result in a performance reduction that depends on the operating conditions of the engine, and is, for example dependent on the prevailing ambient conditions and the load of the gas turbine. This paper attempts to reflect the state of the art theoretical and practical results.
Aerodynamic Design and Performance Analysis of a Vaneless Counter-Rotating Fan and Compressor
Authors: Ren Xinyu , Shen Yuxin , Zhang Tao , Li Jiabin , Ji Lucheng 
Published: August 2024

Abstract
The vaneless counter-rotating fan/compressor can effectively reduce the axial length and gyro torque of the engine. However, the absence of the stators can lead to a frequently changing incidence angle at the downstream, which deteriorates the offdesign performance. Moreover, this characteristic deteriorates with the increase of the tangential velocity at the blade tip. In this paper, taking advantage of the low circumferential speed at the root of the fan blade of the small-sized turbofan engine, the fan and compressor were designed as a counter-rotation scheme without a stator.
Firstly, the performance of the vaneless counter-rotating fan/compressor are analyzed through the velocity triangle. Then, an one-dimensional design program for the vaneless counter-rotating fan/compressor is developed to optimize the design parameters. Finally, a small size vaneless counter-rotating fan/compressor is designed with its design point efficiency of 85.1% and pressure ratio of 3.16. Results show that the relative inlet flow angle towards the downstream rotors varies less than that in conventional compressors, while the incoming flow velocity would increase by 1.5 to 3 times compared to conventional ones. Thus, the hub ratio and speed ratio of a counter-rotating fan/compressor have a sensitively effect on its efficiency and stall margin. Moreover, a reduction in speed ratio could improve the efficiency and stall margin of the counter-rotating fan/compressor, and the speed ratio should be set as a compromise value under the design restrictions.
Multi-Fidelity Aeromechanical Design Framework for High Flow Speed Multistage Axial Compressors
Authors: Nigro Rémy , Baert Lieven , Nyssen Florence , de Cazenove Jean , Dominique Joachim , Lepot Ingrid , Veglio Monica , Princivalle Rémy 
Published: August 2024

Abstract
The development of novel engine architectures is vital in achieving the aviation sector’s net-zero carbon emission target by 2050. With today’s digital decade providing support for an accelerated technology maturation, the challenge for turbomachinery design remains to significantly push the limits of current performance within an ambitious development lead time. In this context, it is essential to adopt a design framework where the predictive models or simulations employed target a sufficiently reliable performance assessment. These models must be tailored to the dynamics of an evolving industrial design process, and therefore continuously balance required design flexibility, robust evaluation, appropriate fidelity (i.e. the level of detail and accuracy they provide), and resulting evaluation time.
This paper discusses a framework for designing axial compressors and its application to the aeromechanical optimisation of a high-speed compressor rotor. The design environment integrates geometry parametrisation, a modular evaluation with different levels of fidelity for the aerodynamic and structural models, and surrogate-based optimisation (SBO) capabilities. It is shown how the combination of a modular sequencing of the different models and the acceleration enabled by high-performance computing (HPC) and machine learning allows for a more advanced preliminary design. A significant gain in isentropic efficiency is attained while satisfying all structural constraints. At the same time, it is demonstrated that the framework is compatible with the characteristics of the preliminary design phase: both in its ability to adapt to cycle and design changes as well as regarding the turnaround time of the optimisation itself.
Numerical and Experimental Aeromechanic Study in High Frequency Domain of Hydrogen Compressor
Authors: Shanmugam Venkatachalam Ravi , Ganiger Manjush , Toni Lorenzo , Guglielmo Alberto , Biliotti Davide , Miris Lorenzo 
Published: August 2024

Abstract
Hydrogen economy is no more a futuristic need, rather it is the need of the hour to combat climate change. However, the scale, accessibility and price of the clean fuel are the main challenges to be overcome for its widespread adaptation. In order to accelerate the journey towards net-zero, the compression, storage and transportation of hydrogen are going to be critical to balance the supply and demand scenarios, and to ensure hydrogen enters new energy markets like refueling stations, green ammonia production and power generation, apart from the existing markets like fertilizer industry.
Hydrogen being the lighter and low-density gas, its compression with traditional technologies such as centrifugal and reciprocating compressors demand new design philosophies to meet the new energy market’s needs. New generations of high efficient centrifugal compressor stages are needed to meet such requirements, including a new target for the peripheral speed that has to be increased beyond the current limits to reach a high head rise per stage.
This paper presents numerical and experimental aeromechanic studies on high peripheral speed impellers for hydrogen centrifugal compressors. High frequency mode shapes that are typical for these applications were excited at low peripheral speed using an innovative approach. Under similitude condition, the experimental studies were carried out at Authors’ internal test facility, revealing that even at low speed, the higher frequency domain, like hydrogen compression one, can be properly excited.
Steady state and transient numerical simulations were carried out, considering a complete stage composed by the upstream return channel, the impeller, the diffuser, and the downstream return channel. The results were then compared against the experimental outcomes, obtaining a successful validation that will be widely discussed in the paper.
Blade Designs for Improved Multi-Phase Performance in sCO2 Compressors: Part I - Design and Numerical Evaluation at Application Relevant Conditions
Authors: Hosangadi Ashvin , Weathers Timothy , Cepero Antonio , Cooper Paul , Fernandez Erik , Kapat Jayanta 
Published: August 2024

Abstract
Design changes to improve the performance of MWe scale sCO2 compressors by delaying the onset of phase change at the leading edge have been evaluated. The design changes involve modifications to the leading edge suction surface of the blade and are referred to as a biased wedge blade. Simulations were performed with the CRUNCH CFD® software tool that has been matured to accurately model near critical real fluid effects in sCO2. Simulations in a stationary cascade compared well with test data and confirm that the biased wedge design reduces the velocity acceleration on the suction surface. Numerical parametric studies at higher velocities in the range of inlet tip speed for MWe scale compressors indicate that the biased wedge design can suppress the onset of phase change in this regime and preserve single phase supercritical flow. These designs can potentially be retrofitted into existing compressor models since this design change is agnostic to the specifics of the design paradigm.
The Effects of Casing Profile on the Aerodynamics of Integrated Intermediate Turbine Ducts
Authors: Hou Jiangdong , Duan Xiaozhi , Kang Ziyu , Yi Yu , Zhou Chao 
Published: August 2024

Abstract
To reduce the engine’s length and weight, the concept of integrated intermediate turbine duct (IITD) is proposed, in which the first row of the low-pressure turbine vanes are replaced by the turning struts in ITD. The effects of the casing profile on the flow features and loss mechanism in the IITD are investigated by experimental, numerical and theoretical methods. In the baseline case, the casing passage vortex at the exit of the IITD is featured with two branches, which is caused by the entrainment effect of the suction side leg of horseshoe vortex near casing. By making the casing profile upstream of the leading edge more downward convex, the thickness of the casing boundary layer can be reduced, and the horseshoe vortex is weakened. The structure of the exit casing secondary flow is thus more complete. In the IITD with higher mean rise angle, the entrainment effect has the ability to reduce the low-momentum fluid and suppress the separation on the suction surface. A method of controlling the casing secondary flow is proposed accordingly. To analyze the loss mechanism, the loss is broken down into the parts generated by mean vortex and turbulence theoretically. The casing boundary layer acceleration can lead to larger velocity gradient and loss caused by mean vortex. While the turbulent dissipation will be reduced on the other hand. Large turbulent dissipation can also be generated when the mixing between the casing secondary flow and wake is enhanced.
Optimal Control Allocation for Distributed Electric Propulsion in a Series/Parallel Partial Hybrid Powertrain
Authors: Litt Jonathan S. 
Published: August 2024

Abstract
The SUbsonic Single Aft eNgine (SUSAN) Electrofan is a NASA concept transport aircraft representative of technology anticipated for a 2040 entry-into-service date. The powertrain consists of a single thrust-producing geared turbofan engine with generators driving a series/parallel partial hybrid power/propulsion system. The architecture includes 16 underwing contrarotating fans, eight on each side. The distributed fans can be used by the flight control system to augment or replace the rudder function. This paper sets up the optimal control problem of setpoint determination for individual wingfans in the distributed propulsion system, accounting for electrical string efficiencies, saturations, and failures. The solution minimizes power consumption while maintaining thrust and torque on the airframe for maneuvering. Additionally, thrust that would have been lost due to temporary fan speed or power saturation is optimally redistributed to maintain overall desired thrust and torque on the aircraft. A simulation of a coordinated turn utilizing the distributed electric propulsion for yaw rate control in a multiple wingfan failure scenario demonstrates the robustness of the powertrain design to failures and helps define its limitations.
Synergetic and Performance Characteristics of a High-Speed Pre-Cooled Propulsion Concept
Authors: Chatzistefanou Athanasios , Tsentis Spyros , Kalfas Anestis 
Published: August 2024

Abstract
Pre-cooled air-breathing cycles are promising candidates to power future high-speed flight as well as Single-Stage-To-Orbit vehicles, due to their increased efficiency over contemporary propulsion systems and launch vehicles. These concepts usually feature complex interactions in the synergy of their thermodynamic cycles, which are not yet well understood, especially at off-design conditions. In this study, a performance model for a pre-cooled, hybrid, air-breathing, rocket-cycle engine is developed for its air-breathing mode of operation. One-dimensional thermodynamic modeling is employed within a component-level approach, to evaluate the performance and operation of the cycle under investigation in the range of 1.35 ≤ M∞ ≤ 5 and conditions of up to 26 kilometers altitude. The model is validated quantitatively and qualitatively for both design and off-design conditions. The specific impulse Isp and specific thrust Fspec, as predicted by the model, agree within less than 5% for the design-point conditions at M∞ = 5. At off-design conditions, the model captures the trend of Isp and agrees within less than 1% with respect to the data for the maximum value of Isp. The maximum gross thrust Fgross point is predicted correctly at M∞ = 4. The fundamental operating principles and synergetic characteristics of the engine at design and off-design conditions are investigated and reported. Parametric analyses quantify the influence of the engine’s parameters on the leading performance metrics. A model which does not feature a bypass duct is created and compared for the same inflow conditions and mission profile. It is found that the engine without the bypass duct exhibits reduced specific impulse which can be up to 32% lower at off-design conditions. In addition, the corresponding fuel mass flow rate to achieve the same mission is increased by a factor of 1.5. It is demonstrated that the overall trend of engine efficiency cannot be properly captured without modeling of the bypass duct, especially at the region of M∞ &lt; 3.5, where the ramjet-like operation is critical. This highlights the importance of the bypass, which is typically neglected in the modeling of such high-speed, combined-cycle systems.
Thermohydraulic Performance and Flow Structures of Diamond Pyramid Arrays
Authors: Corbett Thomas M. , Thole Karen A. 
Published: August 2024

Abstract
Surface features are a common heat transfer enhancement method used in a myriad of applications including gas turbines and heat exchangers. One such style of surface features is diamond pyramids, which offer significant heat transfer augmentation for moderate increases in overall pressure losses. This study investigated a suite of additively manufactured pyramids in a variety of sizes and arrangements at relevant scale contained in test coupons. Designs were printed with low surface roughness relative to typical additive components (Ra &lt; 5μm), and pyramids were printed within 100 μm of the design intent. Experimental and computational results indicate that the pressure penalty and heat transfer increased as the pyramids increased in size with aligned pyramids on both channel walls having higher values than staggered pyramids. It was found that implementing the pyramids onto a rough surface had a lesser impact on the friction factor than implementing on a smooth surface, but that the relative increase in heat transfer was the same regardless of the roughness of the endwall. The greatest enhancement to local heat transfer and pressure loss was offset from the location of minimum flow area due to local acceleration around the wake regions. The vortices formed in the wake of the pyramid structures enhanced the endwall heat transfer and shear stress. The performance of the pyramids investigated in this study follows a similar trend to prior studies investigating smooth rib geometries, though certain rib designs had higher heat transfer at lower pressure losses.
Considerations for Hydrogen Fueled Aerospace Gas Turbine Combustion Sub-System Design
Authors: Clemen Carsten , Ravikanti Murthy , La Bianca Nicholas , Eggels Ruud , Wurm Benno , Young Kenneth 
Published: August 2024

Abstract
As part of its commitment to the decarbonization of the aviation sector and the UN Race to Zero global campaign, Rolls-Royce is actively developing hydrogen combustion gas turbine engine technology capable of powering a range of aircraft from 2035 onwards. These innovative technologies are undergoing integration and validation through a demonstrator project, which involves the modification of a Pearl15 engine for ground testing with gaseous and liquid hydrogen.
The design of an aerospace combustor needs to satisfy conventional requirements such as cost, weight, aero-thermal performance, and lifespan. However, the introduction of hydrogen as the primary fuel introduces additional challenges, including potential novel failure modes, operability considerations and pollutant emissions.
The NOx emissions resulting from hydrogen combustion are currently the subject of extensive research and are considered, to be one of the key considerations which will ultimately influence the design of the optimum hydrogen combustion sub-system for aerospace applications.
This paper describes the development of the first prototype combustion technology at Rolls-Royce. Innovative fuel injection concepts were investigated to enable operation with 100% hydrogen on the Pearl 15 combustor architecture which is to serve as the test vehicle for ground demonstration in the Clean Aviation Project “CAVENDISH”. The paper details the process which began with prototype development and validation on a single sector atmospheric test rig to map the design space and understand sensitivities. This allowed the selection of four leading configurations based on NOx emissions, flame stability (measured using optical methods), ignition and weak extinction performance.
The four configurations were then tested in a single sector, intermediate pressure rig testing at engine-representative low power conditions. This testing aimed at identifying challenges related to flame stability and combustor temperature distribution, thereby mitigating risks associated with engine combustor testing. Finally, tests were undertaken in a full annular, high pressure combustion rig at engine-representative maximum takeoff conditions.
Aerothermal performance, as measured by NOx emissions, weak extinction and exit temperature traverse, demonstrated promising comparisons to kerosene-based fuel. These results demonstrate that a retrofittable combustion solution is credible and realistic for a minimum viable hydrogen gas turbine product.
Determination of Vibration Properties and Reliable Frequency Estimation for Synchronous Vibrations Through Improved Blade-Tip-Timing Techniques Without a Once-per-Revolution Sensor
Authors: Sasakaros Marios , Mann Luca , Schafferus Markus , Wirsum Manfred 
Published: August 2024

Abstract
Synchronous vibrations, which are caused by periodic excitations, can have a severe impact on the service life of impellers. Blade-Tip-Timing (BTT) is a promising technique for monitoring synchronous vibrations due to its non-intrusive nature and ability to monitor all blades at once. BTT generally employs an Once-per-Revolution (OPR) sensor that is mounted on the shaft for blade identification and deflection calculation. Nevertheless, OPR sensors can be unreliable as they may be affected by shaft vibrations and their implementation can be restricted by space constraints. Moreover, the low number of BTT sensors typically leads to under-sampled deflection signals, which consequently hinders the estimation of the vibration frequencies due to aliasing problems. For this reason, BTT is commonly accompanied by strain gauge measurements on some blades.
In this paper improved BTT techniques are presented, which enable the determination of vibration properties of synchronous vibrations without the need for an OPR sensor and ensure a reliable frequency assessment. Specifically, the blades are identified by unique characteristics resulting from manufacturing tolerances while the blade deflections are calculated through a novel method, which relies on the impeller’s circumferential position. Subsequently, by employing approaches based on Non-Uniform Fast Fourier Transform the vibration frequency is accurately estimated. Finally, the vibration properties are determined using regression models. The proposed BTT techniques are validated through comparison with a commercial BTT system as well as SG measurements using experimental data acquired from a turbocharger test bench. The proposed methods eliminate the need for an OPR sensor and parallel strain gauge measurements.