bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison Between Gradient-Free and Gradient-Based Optimizations of the SRV2 Radial Compressor
Authors: Châtel Arnaud , Verstraete Tom 
Published: September 2023

Abstract
This paper investigates the potential multimodality of a radial compressor optimization problem by comparing gradient-free and gradient-based methods in terms of results and computational cost. The turbomachinery application consists in a multipoint optimization of the well-known SRV2 radial compressor. The objective of the optimization is to maximize the total-to-total efficiency of the compressor at peak efficiency while maintaining the operating range of the original impeller. The geometry of the compressor is parametrized using 44 design variables and the fluid domain is automatically discretized using a multi-block structured mesh. The evaluation of the aerodynamic performance is performed using a steady-state RANS CFD solver with the Spalart-Allmaras turbulence model. Gradients of the cost functions with respect to the design variables are, when needed, efficiently evaluated with a discrete adjoint solver.
Multimodality, i.e. the existence of multiple local optima within the design space, is currently widely debated and plays an important role in the selection of the optimization method. The present study shows that both optimization algorithms converge to the same solution which seems to suggest that the design space is unimodal for the considered optimization problem.
Investigation of Fuel and Load Flexibility of an Atmospheric Single Nozzle Jet-Stabilized FLOX® Combustor With Hydrogen/Methane-Air Mixtures
Authors: Petry Niklas , Mannazhi Manu , Yin Zhiyao , Lammel Oliver , Geigle Klaus Peter , Huber Andreas 
Published: September 2023

Abstract
In this work, an existing single nozzle FLOX® [1] burner was modified with a fuel nozzle that was installed concentrically inside the outer air nozzle and was arranged in two different configurations. In the first, non-premixed case, the fuel and air nozzles were flush at the nozzle exit. In the second, technically premixed case, the fuel nozzle terminated 50 mm below the air nozzle exit. A third, fully premixed case was also achieved by injecting fuel into the air delivery line via an inline-mixer upstream of the nozzle exit. Additionally, measurements were performed using fuel nozzles with two different sizes. For all these cases, hydrogen volume fraction in the fuel was varied from 0 to 100 % at a constant equivalence ratio and thermal power. The resulting flames were characterized using 2D OH-chemiluminescence measurements. In addition, load-flexibility was investigated on the 100 vol.% H2 case by varying the equivalence ratio. Some selected conditions were further investigated using particle imaging velocimetry (PIV) to obtain velocity fields. The experimental results demonstrated a strong influence of nozzle configurations (mixedness), equivalence ratio and H2-content on flame shapes. First of all, increasing H2-content reduced the flame lift-off height above the nozzle exit for all three configurations. Secondly, for the cases with 100 vol.% H2 and independent of the nozzle configuration, the lift-off height increased drastically when Φ was reduced to below 0.3 while the flame became visibly unstable. Overall, increasing level of mixedness generally caused the flame to stabilize closer to the nozzle exit. A remarkable decrease in the lift-off height was observed for the technically premixed case compared to the non-premixed case. Increasing H2-content from 0 to 100 vol. % also increased the measured NOx emission by nearly a factor of 4, which was also strongly affected by the level of mixedness. Experimental results from this work are being used in a joint effort to validate numerical models for jet-stabilized hydrogen combustion.
Preliminary Design of Two-Phase Turbo-Expanders for Partial Evaporation Organic Rankine Cycle Power Systems
Authors: Tammone Carlotta , Parisi Simone , Haglind Fredrik 
Published: September 2023

Abstract
The partial evaporation organic Rankine cycle has been shown to be able to improve significantly the net power output of organic Rankine cycle power systems by expanding a fluid in two-phase conditions instead of a saturated or superheated vapor. However, the design of turbo-expanders for this application has not been undertaken yet, due to the complex fluid-dynamic modelling and the structural challenges posed by two-phase flows. This paper aims to provide a first insight into the preliminary design of two-phase axial turbines for partial evaporation organic Rankine cycle power systems by implementing two-phase flows features into a validated mean-line model for axial turbine design. The most important phenomena caused by the presence of a two-phase flow in the cascades are modelled based on the results from previous work conducted on wet steam turbines and on particulate flows in turbomachinery. The modelled phenomena include the deposition of droplets on the blades with the subsequent generation of a liquid film and the mixing between the bulk flow and the generated liquid film downstream the blade trailing edge. The effect of the presence on the two-phase flow on various losses is discussed in the work and the influence of the liquid film is investigated. The results suggest that the impact of the mixing loss on the designed geometries and their performance is significant. However, the decrease in efficiency is significantly mitigated by the reduction of droplets deposition. Therefore, the results from this paper will serve as a basis for future more fundamental research work on the deposition phenomenon and liquid film motion.
Experimental Analysis of Additive Manufactured Latticework Coupons
Authors: Castelli Niccolò , Sandri Umberto , Picchi Alessio , Facchini Bruno , Morante Francesco , Cubeda Simone 
Published: September 2023

Abstract
The capabilities and the precision of additive manufacturing processes have been tremendously increased in the last years, and this trend is not expected to be close to an end. Researchers, in the gas turbine industry, are focusing on the technology implementation on cooling systems. The aim of the present work is to investigate the performances of eight different geometries in order to exploit the cooling potential of some challenging latticework schemes with respect to traditional ones such as smooth channel, dimples and pin fins. Test coupons consisting of those cooling structures embedded inside a rectangular cooling channel with dimensions of 56mm width, 5mm height and 68mm length were fabricated by means of Direct Metal Laser Melting (DMLM) technique.
Since an aim of the present work is to evaluate the shape deformation associated with this additive process, the results of CT scan imaging technique are presented. The performances are characterized both in terms of averaged heat transfer and friction factor values inside the test coupons by means of steady-state technique with a constant wall temperature boundary condition. The investigated flow Reynolds numbers range from 18000 to 40000. These values allow the authors to provide a deeper understanding of the latticework structures performances at Reynolds numbers beyond the range typically investigated in the literature. An efficiency index is employed to compare the performances of each geometry. Although the obtained results reveal that none of the tested geometries outperforms the other ones, the latticework arrangements show a heat transfer enhancement with respect to a porosity decrease. In addition, the good capability in terms of heat transfer of the lattice structures measured in the present work suggests the use of such technologies for twofold optimization process based on mechanical resistance and heat transfer characteristics.
Advantages of Machine Learning Methods in Aerodynamic Blade Optimization
Authors: Beqiraj Klajdi , Perrone Andrea , Sanguineti Marco , Ricci Gianluca 
Published: September 2023

Abstract
The present paper describes the advantages of using Machine Learning methods within the aerodynamic optimization of blades, highlighting the benefits of such techniques in terms of both design time, and expected performance. The case study considered is the NASA Rotor 37.
The automatic parameterization of entire datasets through the use of variational autoencoders, a specific type of Neural Network, is explained and discussed. The autoencoder latent parameters describe the blade 3D geometry and can be used as an alternative to the standard geometric parameters in describing the shape of each sample. The main advantage is that autoencoders enable an automatic parameterization of 3D geometries, thus overcoming the limits imposed by manual parameterization.
The performance prediction (efficiency, pressure ratio) is carried out through a specifically developed Neural Network, properly trained.
The aerodynamic optimization is performed using a Genetic Algorithm: by acting on the latent parameters, the algorithm generates new optimized blades, automatically meshed, verified through CFD simulation, and added to the starting database, with a re-train of the artificial intelligence algorithms. This loop is carried out several times until efficiency is maximized.
Finally, a comparison with a classical optimization based on standard geometric parameters is reported and the results are deeply discussed and analyzed.
Advanced Modelling of Flow and Heat Transfer in Rotating Disc Cavities Using Open-Source CFD
Authors: Wang Ruonan , Gao Feng , Chew John W. , Marxen Olaf , Sun Zixiang 
Published: September 2023

Abstract
Code_Saturne, an open-source computational fluid dynamics (CFD) code, has been applied to a range of problems related to turbomachinery internal air systems. These include a closed rotor-stator disc cavity, a co-rotating disc cavity with radial outflow and a co-rotating disc cavity with axial throughflow. Unsteady Reynolds-averaged Navier-Stokes (RANS) simulations and large eddy simulations (LES) are compared with experimental data and previous direct numerical simulation (DNS) and LES results. The results demonstrate Code_Saturne’s capabilities for predicting flow and heat transfer inside rotating disc cavities. The Boussinesq approximation was implemented into the code for modelling centrifugally buoyant flow and heat transfer in the rotating cavity with axial throughflow. This is validated using recent experimental data and CFD results. Good agreement is found between LES and RANS modelling in some cases, but for the axial throughflow cases, advantages of LES compared to URANS are significant for a high Reynolds number condition. The wall-modelled large eddy simulation (WMLES) method is recommended for balancing computational accuracy and cost in engineering applications.
Experimental Investigation of the Effect of Superheated Liquid Fuel Injection on the Combustion Characteristics of Lean Premixed Flames
Authors: Izadi Saeed , Zanger Jan , Baggio Martina , Seliger-Ost Hannah , Kutne Peter , Aigner Manfred 
Published: September 2023

Abstract
The effect of superheated liquid fuel injection on the performance and emissions of a single nozzle combustor was investigated. Combustion of the lean premixed flames was achieved using a combination of jet and swirl as a stabilization method. In a non-reactive setup, the optimum transition temperature of Jet A-1 fuel from liquid to superheated vaporized state was analyzed. In a subsequent reactive setup, a series of tests were conducted with the liquid fuel at low and elevated temperatures. The experiments were conducted at ambient pressure and various air and fuel preheat temperatures, axial swirlers, thermal powers, adiabatic flame temperatures, and flame tube diameters. Concentrations of nitric oxide (NOx) and carbon monoxide (CO) in the flue gas were measured. The operating conditions were systematically selected according to the Design of Experiments (DOE) method. The results showed that the adiabatic flame temperature caused the most significant change in combustion emissions and the position and shape of the reaction zone, while the superheated fuel injection had only a minor effect because the liquid fuel droplets were largely vaporized before entering the reaction zone through the integration of a swirler and a prefilmer. The use of the axial swirler and prefilmer allowed the combustor to operate in both spray and fully vaporized fuel conditions. As a result, very low emission concentrations of NOx (≈ 5 ppm) and CO (≈ 6 ppm) were achieved. The median flame length and height above the burner of the characterized flames showed competitive values of 32 and 50 mm, respectively. Lean blowout limits of less than 1500 K were achieved. Two different flame modes were observed during the experiments. By increasing the bulk velocity of the combustor, its hysteresis was resolved, resulting in stable and reliable flames with a wide low-NOx operating range.
Investigation on Process Architectures for High-Temperature Heat Pumps Based on a Reversed Brayton Cycle
Authors: Kabat Nancy , Jende Enrico , Nicke Eberhard , Stathopoulos Panagiotis 
Published: September 2023

Abstract
Heat pumps are a core technology for the decarbonization of industrial process heat. High-temperature heat pumps (HTHP) typically upgrade waste heat of industrial processes. This way they can simultaneously electrify process heat and reduce the respective primary energy consumption. The utilization of renewable electricity to drive HTHP additionally results in decarbonization of process heat supply. Commercial industrial heat pumps supply process heat at temperatures up to approximately 150°C. However, several studies have shown that process heat can be also supplied with HTHP at temperatures above 150°C. The economic and environmental performance of HTHPs depend strongly on their process architecture and their integration into the industrial process they supply with heat. This paper focuses on the investigation of high-temperature heat pump process architectures based on the reversed Brayton cycle with air as the working medium. The process architecture of the HTHP pilot plant at the Institute of Low-Carbon Industrial Processes of the German Aerospace Center (DLR) is presented and used as a reference. The current work investigates the heat source and heat sink integration in the heat pump cycle architecture and methods to effectively break down the compression and expansion processes to optimize performance for a heat sink temperature of 250°C. To analyze and compare the results, fixed boundary conditions valid for all architectures are made.
Optical Diagnostics for Aerospace and Turbomachinery Applications
Authors: Guimarães Bucalo Tamara , Ribarov Lubomir 
Published: September 2023

Abstract
Understanding the properties of complex reacting and non-reacting fluid flows is important for quantification and determination of parameters such as pressures, temperatures, velocities, and densities among many others. The use of conventional (intrusive) technologies, while sufficient in a limited way (and for simpler flows), may be overextended for more complex experimental flows (e.g., high-speed, high-temperature, etc.). The development and application of advanced non-intrusive (minimal/no-contact) optical diagnostics has offered the extended opportunities to successfully interrogate such complex flows. In this review paper, a broad consideration of some of the developed advanced optical diagnostics techniques is considered, including both seeded and unseeded methods. Applications to aerospace, combustion, and turbomachinery of the various optical diagnostics methods are discussed in an effort to summarize some of the advantages and challenges for each particular optical diagnostic method.
Study on Anti-Crossflows Characteristics of Jet Shape and Inclination in Multiple Jet Impingement Cooling
Authors: Hu Qingsong , Wang Yi , Yang Kefeng , Gao Shanghong , Wang Xiangyu , Feng Zhenping 
Published: September 2023

Abstract
Multiple jet impingement is one of the most efficient methods in the field of internal heat transfer enhancement. It provides a large heat transfer efficiency and a more uniform heat transfer distribution when cooling a large area of surface. This paper investigated the anti-crossflows characteristics of jet shape and inclination on multistage impingement channel. In order to reduce the adverse influence of upstream accumulative crossflow on downstream impingement heat transfer, two novel impingement jets, the Capsule and X-shape jets, were developed. On this basis, the flow and heat transfer characteristics of jet shape and inclination on multistage impingement channel were analyzed. The results indicated that with the development of the crossflow, the vortex and detached flow formed by the interaction of crossflow and impingement jet was a significant factor affecting the downstream impingement heat transfer. Once the intensity of the vortex developed to the point where it could pass through the downstream impingement core heat transfer region, the jet can no longer directly transfer heat with the target surface, resulting in the deterioration of downstream impingement heat transfer. The impingement jet hole with an inclination angle could offset the adverse influence of the crossflow on the downstream heat transfer and improve the heat transfer efficiency, due to the existence of the momentum component against the crossflow. Compared to the Circle and Capsule jet, the X-shape jet with jet inclination exhibits the best enhanced heat transfer performance and anti-crossflows characteristics. Considering the pressure drop and enhanced heat transfer effects comprehensively, the comprehensive performance of the X-shape jet with 0° inclination was the optimal, and its comprehensive heat transfer factor increased by 1.81% at a high Reynolds number compared with the reference case.
Multidisciplinary Assessment of Foreign Object Damage (FOD) Sensitive Regions on a Compressor Rotor Blade
Authors: Rocchi Simona , Roth Christian , Froebel Tobias , Hackenberg Hans-Peter , Gümmer Volker 
Published: September 2023

Abstract
During takeoff and landing, aero engines often ingest foreign objects which can damage the airfoils. These events can have a significant impact on the safety of the engine, particularly due to the operating load condition of gas turbines throughout their service life. In addition, the appearance of dents or cracks along the blade leads to surface damage, which in turn affects the structural mechanics integrity and the overall aerodynamic performance. In order to prevent safety concerns and high maintenance costs, blades with improved FOD robustness are being sought. In this prospect, the prediction of airfoil regions with high sensitivity to FOD plays a crucial role for later optimization. The aim of this work is to identify these areas, focusing on two aspects: the detection of airfoil regions with the highest probability of foreign object impact, and the evaluation of FOD critical areas through structural mechanics and aerodynamics evaluation. The first objective was achieved with the creation of a surface defect map obtained using a white light scanning technique. The structural mechanical investigation involved the numerical calculation of the stress concentration factor, which predicts the allowable stress increase caused by a local damage. From the aerodynamic perspective, the same assessment was carried out by placing a sample FOD at six positions along the airfoil edge. By comparing the compressor performance for the same damage at different heights, the most sensitive region was identified. Finally, the achieved multidisciplinary overview highlights potential regions to be optimized in future airfoil design in order to increase the overall robustness against FOD.
Condenser Retrofit in Leibstadt Nuclear Power Plant (BWR) - Far Beyond a Standard Modular Solution
Authors: Wolf Hartwig , Wettstein Arthur , Faltermeier Robert , Graf Peter , Schupp Daniel 
Published: September 2023

Abstract
The Leibstadt nuclear power plant (KKL) in Switzerland was originally commissioned in 1984 with a nominal power output of 1000 MWel. Since then, there have been several uprates of the boiling water reactor (BWR) which have increased the power to 1275 MWel.
After the nearly four decades of operation, the original condenser was impacted by advanced erosion corrosion and by progressive performance deterioration. In addition, the thermal power uprates required load reduction during hot summer periods to avoid high condenser back pressure.
Consequently, KKL asked GE to carry out a comprehensive retrofit study to identify potential improvements on both lifetime and performance. These included: robust material selection considering cycle chemistry and cobalt limitations; optimized extraction of non-condensable gases by means of a bespoke air cooler section of the condenser; and applying GE Steam Power’s latest innovative tube pattern design which is aligned to BWR requirements and simultaneously optimizes the condensation area together with the steam flow paths.
However, site constraints prevented the use of a typical modular condenser retrofit as both the local access in the machine house was very restricted and modifications of the concrete walls of the radiation shielding had to be avoided. Hence, working in a close cooperation between KKL and GE Steam Power, a customized retrofit concept was developed which used semi-prefabricated skeletal modules and an on-site rebuild of the condenser.
This paper provides details of the solution, particularly of the improvements which are specific to condensers operating in a BWR plant. Also described is the preparatory and complementary refurbishment work which was executed at the system interfaces. This includes replacement of strongly eroded condenser neck parts, an external reinforcement of the condenser walls, and modification of the continuous tube cleaning system. The construction site work itself is also described. This includes the required safety measures, the complex work logistics, the development of specific installation tools for handling and turning the skeletal modules, and the compliance with treatment rules for contaminated material.
In total, approximately 475 tons of old condenser material were dismantled, 24 new semi-prefabricated skeletal modules were installed, a condenser with 51’600 tubes was rebuilt on-site and 8 waterboxes were replaced with an improved design made of stainless steel. More than 350 professionals contributed to the successful retrofit with an overall site effort of 270’000 working hours — all without any major accident.
Key success factors for this retrofit have been the close and efficient cooperation between an experienced and knowledgeable customer with an OEM supplier bringing their expertise in engineering and construction during all project phases, and the very detailed planning and preparation phase.