bluuebunny/crossref_metadata_2025_split huggingface dataset:
A CFD Study on the Performance of Modified H-Shaped VAWTs for Tilted Operation Condition
Authors: Kouaissah Otman , Franchina Nicoletta , Persico Giacomo 
Published: August 2024

Abstract
Wind energy harvesting may see a radical transformation with the introduction of new wind turbine concepts. In fact, the vertical axis configuration offers significant advantages that may accelerate extending the installation capabilities to deep waters, where only floating platforms are feasible and economically convenient. While experimental tests for multi-objective assessment are expensive in terms of costs and time, and analytical methods relying on Blade Element Momentum (BEM) are of limited fidelity, especially when considering novel rotor configurations, advanced simulations carried out using high-fidelity Computational Fluid Dynamics (CFD) techniques are a promising tool for evaluating the aerodynamic performance of wind turbines. CFD simulations enable critical evaluation of real-time, long-term aerodynamic loading and prediction across various operational scenarios. This technique can thus be crucial for optimizing the efficiency of wind turbines and reducing the LCOE.
This paper presents a fully 3D CFD investigation on the aerodynamics and near-wake development of a small-scale H-shaped VAWT and two modified versions, adapted for operating in tilted conditions, which is typical for spar-buoy applications. An in-depth spanwise study of the three versions at the peak power condition is performed. The difference in the swept area and the coning angle effect in combination with the tilt condition are considered. The obtained results have shown the potential to contribute to the ongoing development and advancement of the Floating-VAWT technology. The vortical structures development is also commented to provide better understanding of the physical phenomena taking place. Since the relevant energy harvesting capability being predicted for the newly designed turbines, further simulations aimed at demonstrating the engineering relevance of the machines, utility-scale models of the turbine. The numerical predictions confirm the high performance achievable by the HV-shaped wind turbines, and provide valuable insights for its future installations.
Retrofitting an Existing Combined Cycle Gas Turbine With Post-Combustion Carbon Capture: Assessment of Solvent Selection Impact on Performance
Authors: Verhaeghe Antoine , Bricteux Laurent , Demeyer Frederiek , Blondeau Julien , De Paepe Ward 
Published: August 2024

Abstract
Amine(s)-based post-combustion Carbon Capture (CC) is the most mature and applicable technology to retrofit existing Combined Cycle Gas Turbine (CCGT) assets into low-carbon power plants. However, its deployment is hindered by high CAPEX as well as high OPEX, linked with the energy requirement for the solvent regeneration process, reducing the global plant efficiency. Hence, CC energy penalty reduction is necessary. Next to performing Exhaust Gas Recirculation (EGR), efficient heat integration is a key strategy, involving the extraction of steam from the most suitable location in the steam cycle to supply the CC solvent regeneration heat. The choice of extraction location depends on the required steam quality for solvent regeneration, which, in turn, is influenced by the specific solvent used in the carbon capture process. Therefore, it is imperative to evaluate the different integration strategies for individual solvents and analyse their influence on the overall performance of the plant. In this study, we investigate the use of two distinct solvents: monoethanolamine (MEA), the conventional choice, and a blend of methyldiethanolamine (MDEA) and piperazine (PZ) for CC application to a CCGT. The objective is to conduct a comprehensive comparison between both solvents, examining their heat integration and impact on plant performance for the retrofitting of an existing CCGT with post-combustion carbon capture. To this end, a thermodynamic analysis of a typical CCGT plant equipped with EGR and coupled with an amine(s)-based CC plant has been performed using specific simulation models in Thermoflex and Aspen Plus. Different heat integration strategies are presented and compared for both solvents. Results show that, by extracting steam from the Intermediate Pressure/Low Pressure (IP/LP) crossover, using MDEA/PZ instead of MEA allows to increase the electrical efficiency by 0.5 absolute percentage points, representing an efficiency reduction associated to the CC of 6.2 abs.%. However, extracting steam of higher quality, before the Intermediate Pressure (IP) steam turbine, leads to a more significant performance degradation, with an efficiency penalty of 8.3 abs.%. Consequently, the optimal option for retrofitting existing CCGT with MDEA/PZ-based CC is to extract steam from the IP/LP crossover under full-load operation. Future works will focus on part-load operation of the integrated CCGT-CC.
Compressor Surge Identification in Innovative Heat-Pump Systems Equipped by Vaned Diffuser Centrifugal Compressor
Authors: Niccolini Marmont Du Haut Champ Carlo Alberto , Silvestri Paolo , Reggio Federico , Traverso Alberto , Sishtla Vishnu 
Published: August 2024

Abstract
In the present energy scenario, heat-pumps are assuming an important role to improve energy efficiency in reversible cooling systems. In particular, in case of industrial size plants, centrifugal compressors are preferred with respect to other solutions; nonetheless, they are often subjected to variable operation and therefore they must withstand off-design conditions. For studying unstable operation of refrigerant closed loop systems, Carrier provided the University of Genoa with a small size chiller rig equipped with an innovative high speed centrifugal compressor driven by a variable speed motor. This paper presents the vibro-acoustic signature analysis of such a closed loop rig from a system perspective, mainly focusing on mechanical response of compressor casing. First, its vibro-acoustic characterization is conducted at on-design and stable operation. Afterwards, some surge transients are obtained by progressively closing some valves in plant feeding lines, and meanwhile vibro-acoustic signals are acquired at relevant plant locations to characterize system response just before instability onset. In this way, suitable surge precursors can be defined in incipient surge conditions for early surge detection in this kind of complex plants. Indeed, system dynamics is significantly affected by interposed volumes, and therefore the effect of heat exchangers in system response may be relevant. To this aim, system dynamics is analyzed in detail both in sub-synchronous frequency range and in high frequency region to assess how its vibro-acoustic response varies when moving from stable conditions towards surge. Surge precursors are obtained by relying only on vibro-acoustic signals both in low and high frequency ranges in order to perform early surge detection in such chiller pilot system. The main advantage of the proposed approach is to exploit non-intrusive probes, which allow to define diagnostic indicators without interacting directly with the working fluid, therefore preserving system integrity and reliability.
Investigation of Endwall Secondary Flows in a Low Aspect Ratio Transonic Turbine, Part II: Passage Oblique Shock
Authors: Jennerjohn Christianer Mary K. , McQuilling Mark , McKeever Craig W. 
Published: August 2024

Abstract
With increasing exit Mach number through the transonic regime, increased losses in a turbine can be incurred due to the increase in shock losses. The transonic regime is specifically of interest as it exhibits both a loss bucket behavior as well as the potential for unique trailing edge shedding modes at midspan. As for the endwall secondary flows, there can be increased losses due to the increase in shock interactions with endwall secondary vortices. In this second part of the two part series, the variation in exit isentropic Mach number varied up to 1.15 where the endwall secondary flow development is compared between numerical predictions and experimental results for a low aspect ratio turbine (AR = 0.66 and Zw = 1.0). Experimental results are produced via testing in the SLU linear turbine cascade and include results of airfoil static pressures. Numerical analysis is completed using Cadence Fine/Turbo (RANS modeling with the SST k-omega turbulence closure model) and validated via the experimental data. Numerical predictions include airfoil static pressure loading, passage secondary flow development, shock interactions within the passage, as well as downstream mixing loss characterization. Results show the impact of the exit isentropic Mach number on the shock-vortex and shock-boundary layer interactions affecting the endwall secondary flow development. With increased exit isentropic Mach number, the flow exhibits a transition in the passage shock behavior having a direct impact on the endwall secondary flow development and shock-induced vortices within the passage. However, this work also shows the presence of a shock-vortex interaction with the passage vortex. As a result, the downstream mixing losses are then compared at six downstream planes (0.2 to 3.0Cx) where numerically predicted energy loss is assessed showing the increased rate of production at higher exit isentropic Mach number. The results of this part show evidence and support for a secondary flow model which details the endwall secondary flow development for an oblique shock structure within the transonic regime.
On the Design of a Scaled-Up Pulsed Methane Pyrolysis Reactor for Clean Hydrogen Production
Authors: Bianchini Cosimo , Da Soghe Riccardo , Bertini Davide , Kendrick Donald , Gray Scott , Hinkey John , Aarnio Michael J. , Meloni Roberto 
Published: August 2024

Abstract
In a global hydrogen market rapidly growing to satisfy the requests driven by a Net Zero economy, new solutions for clean and cheap hydrogen production are needed. Ekona has developed a pulsed methane pyrolysis (PMP) hydrogen production system based on a constant volume, combustion-driven process. The PMP reactor is non-catalytic and low-cost and mitigates carbon fouling typical of other methane pyrolysis reactor platforms as proved by the 200 kg of hydrogen/day pilot. A scale-up procedure is on-going to meet the needs of actual applications typically orders of magnitude larger than this initial plant size.
The enclosed paper describes the computational fluid dynamics (CFD) numerical modeling work performed to enlarge the current reactor and combustors, leveraging the lessons learned, up to commercial sizes. Since the process cycle is quite long and complex, the CFD study was broken into three different sections dedicated respectively to: 1) Combustor Mixing, Filling and Purging, 2) Simulated Hot Products Injection into the Reactor, 3) Reactor Filling and Venting and Interaction with concurrent Combustor Activities. Despite sharing a similar numerical method based on transient multi-species CFD simulations with moving meshes exploiting the overset mesh approach to model the valve movement, each section focused on different parts of the cycle (in time) and reactor (in space).
Several geometry variants are tested and ranked in their performance for providing uniform methane/oxygen mixing, obtaining nearly one-dimensional plug flow filling in the combustor, generating adequate mixing between injected combustion products and feedstock in the reactor to uniformly raise pressure and temperature up to pre-pyrolysis conditions, and generating minimal flow anomalies in the reactor to permit smooth feedstock filling and venting due to the interaction with the combustor flow and nozzle tip.
Techno-Economic Analysis of Offshore Wind Power Resources in the Gulf of Aqaba
Authors: Rehman Shafiqur , Ibrahim Nasiru , Irshad Kashif , A. Mohandes Mohamed , Mohammed Abdul Baseer 
Published: August 2024

Abstract
The present work conducted offshore wind power resources assessment (OWPRA) at six offshore locations in the Gulf of Aqaba. The hourly mean wind speed (WS) and direction (WD) data at 100 m above the water surface, in addition to temperature and pressure near water surface level, between 1979 and 2021 (43 years) has been used. Log-term mean WS values at L1 to L6 locations are 5.89, 6.58, 8.34, 7.69, 6.26, and 5.01 m/s and the corresponding wind power density (WPD) (are 221, 263, 547, 394, 205, and 104 W/m2 at 100 m above the water surface; respectively. The windy site identifier index (WSI) with magnitudes of 31.91, 26.17, and 10.12 at L3, L4, and L2 sites further confirms the suitability of these sites as indicated by higher WS and WPD values above. However, the cost of energy, calculated based on an average total installation cost of 4,720.25 USD/kW during 2010 to 2021 are found to be 1.160 USD/kWh and 1.80 USD/kWh, for the best and the worst scenarios corresponding to L3 and L2 sites. The monthly and annual wind variability indices remained &lt; 1 at most of the location, which is an indication of less turbulent windy sites.
A Multi Objective Optimization Framework for Offshore Wind Farm Design in Deep Water Seas
Authors: Barnabei Valerio Francesco , Ancora Tullio Carlo Maria , Conti Michela , Castorrini Alessio , Delibra Giovanni , Rispoli Franco , Corsini Alessandro 
Published: August 2024

Abstract
Floating offshore wind energy will play a key role in the clean energy transition scenario. The number of projects deploying large-scale wind farms is growing in multiple regions, from Northern Europe to the East Coast of the United States, and extending to the Mediterranean Sea. Offshore wind farms face fewer constraints in layout design, as they do not need to consider orography and can generally be situated in vast, open sea areas. Consequently, offshore wind turbines could be arranged in simple layouts, such as grid patterns or staggered rows, spaced uniformly. However, this regular turbine arrangement would result in significant annual energy production (AEP) losses due to wake-rotor interaction. Although increasing spacing between turbines can mitigate this issue, it is not always feasible due to marine space availability. Moreover, when feasible, it can lead to higher costs for additional cabling and maintenance. This paper aims to introduce a multi-objective wind farm optimization framework that employs a genetic algorithm (NSGA II). This framework seeks to maximize the energy production while minimizing OPEX and CAPEX costs, taking into account the wind resource and bathymetry of a specific region. In the paper, two case studies are presented for the optimization of wind farms in the Mediterranean Sea assuming 15MW wind turbines. AEP evaluation of each individual wind farm is obtained with the open-source library FLORIS, while the optimization algorithm relies on the library PyMoo for multi-objective optimization.
Design and Manufacture of EBC Coated SiC/SiC Nozzle Guide Vanes for High-Pressure Turbines
Authors: Süß Fabia , Schöffler Robin , Friedrich Lion , Petersen Anna , Vogel Felix , Frieß Martin , Ebach-Stahl Andrea 
Published: August 2024

Abstract
Increasing the efficiency of jet engines is essential to meet the demanded climate targets. Ceramic matrix composites (CMC) are strong candidates for aircraft applications because they withstand high temperatures, while their density is two-thirds lower than that of conventional nickel-based alloys. This leads to cooling air savings and a lower overall engine weight, resulting in a potential reduction of emissions. To investigate the potential benefits and manufacturing techniques required for the introduction of CMC to the high-pressure turbine of a modern jet engine, the geometry of a nozzle guide vane of an existing turbine was redesigned considering ceramic specific constraints. Then, the liquid silicon infiltration (LSI) process was used to manufacture SiC/SiC nozzle guide vanes. Hi-Nicalon S woven fabric was used together with a CVI-based fiber coating. The outer surface of the vane was ground to meet the requirements for surface roughness, and geometric and positional tolerances. Cylindrical, laser-drilled cooling holes were introduced for trailing edge cooling. In the final step, an environmental barrier coating system (EBC) consisting of yttrium disilicate and yttrium monosilicate layers was applied using PVD processing. Wind tunnel testing under TRL 4 will be performed and vane performance will be evaluated.
Numerical Simulation of a Reacting Hydrogen Jet in a Vitiated Co-Flow Using a Detailed Chemistry Model
Authors: Kulkarni Rohit , Attal Nitesh , Liu Shuaishuai , Shekhawat Yajuvendra , Pomraning Eric , Lee Daniel , Burton Tristan , Senecal Kelly 
Published: August 2024

Abstract
The sequential combustion system in a gas turbine is composed of two complementary combustion stages in series: one premix stage followed by an auto-ignited second stage. This helps in reducing NOx significantly and gives more operation flexibility (lower loads) by redistributing the fuel between the two stages. Staged/sequential combustion is a state-of-the-art method to provide operation flexibility and reduced emissions in gas turbines. A key requisite for such a model is the accurate determination of the flame location to predict emissions, flame dynamics, and temperature distribution. The numerical simulations of such combustion systems must accurately capture auto-ignition and flame propagation to predict the flame position and shape. In this work, the hydrogen lifted flames are simulated using a 2-equation LES model with detailed chemistry and Adaptive Mesh Refinement (AMR). The sensitivity of the flame lift-off height to the co-flow temperature and velocity fluctuations at the inlet is studied. The numerical results of the so-called Cabra H2 flame are validated against experimental [1] and numerical results in the literature [2–8].
Optimization Design of Variable Fillet for Different Boundary Thicknesses in a Highly Loaded Compressor Cascade
Authors: Zhang Gangduo , Zhu Mingmin , Shao Runzhu , Qiang Xiaoqing , Teng Jinfang 
Published: August 2024

Abstract
This paper addresses the aerodynamic challenges associated with the introduction of a hybrid engine, aiming to enhance efficiency and reduce fuel consumption. Focusing on a smaller, higher-loading compressor rear stage, the study explores three critical questions related to pressure gradients, inlet boundary layers, and the scaling of characteristic geometries. Emphasizing the impact of corner separation on compressor efficiency, the research delves into the aerodynamic impact of the fillet in a smaller compressor rear stage cascade.
A numerical study based on a typical compressor stator cascade, NACA65-K48, is presented to elucidate fillet design criteria under varying inlet boundary layer thicknesses. Employing optimization and numerical simulations, the study explores variable fillet geometries and their performance characteristics at different inlet conditions. Flow field analyses at design and near stall conditions reveal the influence of variable fillets on blockage regions and total pressure loss.
The analysis underscores the importance of axial velocity gradient changes influenced by variable fillets, affecting blockage regions and entropy generation. The design criteria of variable fillet for blades operating with end wall blockage are proposed, in consideration of acceleration near suction peak, retraining of separation inside passage and avoiding strong wake after trailing edge. The proposed empirical criteria for variable fillets are validated through simulations on a Controlled Diffusion Airfoil cascade, demonstrating improved performance and flow fields.
Wire EDM for the Manufacture of Fir Tree Slots Using Different Wire Electrodes
Authors: Küpper Ugur , Schulze Brock Daniel , Klink Andreas , Herrig Tim , Bergs Thomas 
Published: August 2024

Abstract
The use of materials with increasing high-temperature strengths for turbine disks brings conventional manufacturing processes to their technical and economical limits. As an alternative manufacturing approach, the wire EDM process was therefore tested in several investigations. Despite the many advantages of this manufacturing process, EDM has significantly lower productivity compared to conventional processes. This can be increased by using enlarged wire diameter of the electrodes (bigger wires). The increased wire diameter improves wear resistance so that higher energies can be used. However, the higher energy input has a negative effect on surface integrity. Especially for safety-critical components, these changes in surface properties must be considered critically. This paper therefore examines the use of bigger wire electrodes for the electrical discharge machining of fir-tree slots on turbine disks. For this purpose, the process performance and surface integrity of Inconel 718 machined by using brass and coated wire electrodes with standard diameters and a new generation of 0.4 mm diameter wire electrodes are compared. Depending on the wire electrode, individual processing technologies are developed and tested with a focus on high productivity and low wire consumption. Finally, a technological and economical assessment is carried out, and the best-performing wire electrode with appropriate technology variant for rough machining a fir tree slot is selected.
Neural Network Based Digital Twin for Performance Prediction of Water Brake Dynamometer
Authors: Song Shuo , Xiao Hong , Jiang Leibo , Liang Yufeng 
Published: August 2024

Abstract
Water brake dynamometer, the core component of aerospace engine testing facilities, is widely used in turbine component testing and turboshaft engine testing. Since the status of the water brake dynamometer system cannot be monitored in detail, equipment maintenance is performed solely based on the operator’s experience, resulting in high risks in the dynamometer equipment operation. Post-test inspections may even reveal damage to the dynamometer bearings and key components. Cavitation and other phenomena require urgent technical solutions to improve health monitoring of key equipment and experimental safety.
This paper proposes a performance prediction method for water brake dynamometers based on machine learning. By conducting physical correlation analysis of key parameters, the characteristics of water brake dynamometer operation are captured. Subsequently, a performance prediction model for water brake dynamometer is built based on digital twin technology and experimental data, enabling an accurate mapping of the dynamometer’s operational state. After turbine test, the digital model is verified by dynamometer operation data set. Predicted operating parameters of the digital model show that the dynamic mean error between predicted values and actual values of multiple core component temperatures is less than 1%. Considering the sensitivity of data changes, these prediction error values are acceptable, which provide valuable reference information.