06 Fakultät Luft- und Raumfahrttechnik und Geodäsie
Permanent URI for this collectionhttps://elib.uni-stuttgart.de/handle/11682/7
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Item Open Access Piloted simulation of the rotorcraft wind turbine wake interaction during hover and transit flights(2022) Štrbac, Alexander; Greiwe, Daniel Heinrich; Hoffmann, Frauke; Cormier, Marion; Lutz, ThorstenHelicopters are used for offshore wind farms for maintenance and support flights. The number of helicopter operations is increasing with the expansion of offshore wind energy, which stresses the point that the current German regulations have not yet been validated through scientific analysis. A collaborative research project between DLR, the Technical University of Munich, the University of Stuttgart and the University of Tübingen has been conducted to examine the sizes of the flight corridors on offshore wind farms and the lateral safety clearance for helicopter hoist operations at offshore wind turbines. This paper details the results of piloted helicopter simulations in a realistic offshore wind farm scenario. The far-wake of rotating wind turbines and the near-wake of non-rotating wind turbines have been simulated with high-fidelity computational fluid dynamics under realistic turbulent inflow conditions. The resulting flow fields have been processed by superposition during piloted simulations in the research flight simulator AVES to examine the flight corridors in transit flights and the lateral safety clearance in hovering flights. The results suggest a sufficient size for the flight corridor and sufficient lateral safety clearance at the offshore wind turbines in the considered scenarios.Item Open Access Icy ocean worlds - astrobiology research in Germany(2024) Klenner, Fabian; Baqué, Mickael; Beblo-Vranesevic, Kristina; Bönigk, Janine; Boxberg, Marc S.; Dachwald, Bernd; Digel, Ilya; Elsaesser, Andreas; Espe, Clemens; Funke, Oliver; Hauber, Ernst; Heinen, Dirk; Hofmann, Florence; Hortal Sánchez, Lucía; Khawaja, Nozair; Napoleoni, Maryse; Plesa, Ana-Catalina; Postberg, Frank; Purser, Autun; Rückriemen-Bez, Tina; Schröder, Susanne; Schulze-Makuch, Dirk; Ulamec, Stephan; de Vera, Jean-Pierre PaulIcy bodies with subsurface oceans are a prime target for astrobiology investigations, with an increasing number of scientists participating in the planning, development, and realization of space missions to these worlds. Within Germany, the Ocean Worlds and Icy Moons working group of the German Astrobiology Society provides an invaluable platform for scientists and engineers from universities and other organizations with a passion for icy ocean worlds to share knowledge and start collaborations. We here present an overview about astrobiology research activities related to icy ocean worlds conducted either in Germany or in strong collaboration with scientists in Germany. With recent developments, Germany offers itself as a partner to contribute to icy ocean world missions.Item Open Access Manufacture and thermomechanical characterization of wet filament wound C/C‐SiC composites(2021) Frieß, Martin; Böyükbas, Muhammed; Vogel, Felix; Cepli, Daniel; Schatz, Oliver; Süß, Fabia; Shi, YuanThe paper presents manufacture of C/C‐SiC composite materials by wet filament winding of C fibers with a water‐based phenolic resin with subsequent curing via autoclave as well as pyrolysis and liquid silicon infiltration (LSI). Almost dense C/C‐SiC composite materials with different winding angles ranging from ±15° to ±75° could be obtained with porosities lower than 3% and densities in the range of 2 g/cm3. Thermomechanical characterization via tensile testing at room temperature and at 1300°C revealed higher tensile strength at elevated temperature than at room temperature. Thus, C/C‐SiC material obtained by wet filament winding and LSI‐processing has excellent high‐temperature strength for high‐temperature applications. Crack patterns during pyrolysis, microstructure after siliconization, and tensile strength strongly depend on the fiber/matrix interface strength and winding angle. Moreover, calculation tools for composites, such as classical laminate and inverse laminate theory, can be applied for structural evaluation and prediction of mechanical performance of C/C‐SiC structures.Item Open Access Dynamic-stall measurements using time-resolved pressure-sensitive paint on double-swept rotor blades(2021) Weiss, Armin; Geisler, Reinhard; Müller, Martin M.; Klein, Christian; Henne, Ulrich; Braukmann, Johannes N.; Letzgus, JohannesThe study presents an optimized pressure-sensitive paint (PSP) measurement system that was applied to investigate unsteady surface pressures on recently developed double-swept rotor blades in the rotor test facility at the German Aerospace Center (DLR) in Göttingen. The measurement system featured an improved version of a double-shutter camera that was designed to reduce image blur in PSP measurements on fast rotating blades. It also comprised DLR’s PSP sensor, developed to capture transient flow phenomena (iPSP). Unsteady surface pressures were acquired across the outer 65% of the rotor blade with iPSP and at several radial blade sections by fast-response pressure transducers at blade-tip Mach and Reynolds numbers of Mtip=0.282-0.285 and Retip=5.84-5.95×105. The unique experimental setup allowed for scanning surface pressures across the entire pitch cycle at a phase resolution of 0.225deg azimuth for different collective and cyclic-pitch settings. Experimental results of both investigated cyclic-pitch settings are compared in detail to a delayed detached eddy simulation using the flow solver FLOWer and to flow visualizations from unsteady Reynolds-averaged Navier–Stokes (URANS) computations with DLR’s TAU code. The findings reveal a detailed and yet unseen insight into the pressure footprint of double-swept rotor blades undergoing dynamic stall and allow for deducing “stall maps”, where confined areas of stalled flow on the blade are identifiable as a function of the pitch phase.Item Open Access Low temperature oxidation of cyclohexane: uncertainty of important thermo-chemical properties(2018) Abbasi, Mehdi; Slavinskaya, Nadezda; Riedel, UweThe study of the standard formation enthalpy, entropy, and heat capacity for key species relevant to the low-temperature combustion of cyclohexane has been performed by applying the group additivity method of Benson. The properties of 18 Benson groups (8 of them for the first time), and 10 ring correction factors for cyclic species were estimated through different empirical and semi-empirical methods. The method validation proceeded through comparison of predicted values for certain number of newly estimated groups and available literature data derived from quantum chemistry estimations. Further validations of the estimated properties of groups have been provided by comparing estimated properties of test species with data in literature and kinetic databases. Also the standard deviation between prediction and reported values has been evaluated for each validation case. A similar approach has been applied for validation of the estimated ring correction groups. For selected well-studied cyclic molecules the predicted values and the literature data have been compared with each other, and the standard deviations have been also reported. The evaluated properties of the cyclohexane relevant species were also compared with similar ones available in other kinetic models and in databases. At the end the estimated properties have been presented in a tabulated form of NASA polynomial coefficients with extrapolation up to 3500 K.Item Open Access Hydroxyl-conductive 2D hexagonal boron nitrides for anion exchange membrane water electrolysis and sustainable hydrogen production(2025) Kaur, Jasneet; Schweinbenz, Matthew; Ho, Kane; Malekkhouyan, Adel; Ghotia, Kamal; Egert, Franz; Razmjooei, Fatemeh; Ansar, Syed Asif; Zarrin, HadisIn response to the urgent global call to transition from polluting fossil fuels to sustainable energy alternatives, hydrogen emerges as a promising and widely accessible energy source if it can be efficiently produced through water splitting and electrolysis. Anion exchange membrane (AEM) water electrolyzers (AEMWEs) have potential for large scale H2 production at a low cost. However, the development of alkaline membranes with high hydroxide conductivity, improved stability and better performance is a significant challenge for the commercial application of advanced AEMWEs. In this work, a novel structure for hydroxide-ion conductive membranes based on surface-engineered two-dimensional (2D) hexagonal boron nitrides (h-BN) is designed and validated in a highly active and durable AEMWE cell with non-precious metal Ni-based electrodes. Among two samples, the high-loaded 2D hBN nanocomposite membrane (M2) showed significantly high hydroxide-ion conductivity (190 mS cm-1) with improved electrochemical and mechanical stability. The AEMWE cell assembled with the M2 membrane exhibited superior cell performance, achieving 1.78 V at 0.5 A cm-2 compared to the cell utilizing the lower loading hBN nanocomposite membrane (M1). Additionally, its performance closely approached that of the cell employing a commercial membrane. During a long-term stability test conducted at a constant load of 0.5 A cm-2 for 250 hours, the M2 membrane maintained satisfactory electrolysis voltage without any notable failure. These findings demonstrate that 2D hBN nanocomposite membranes hold great promise for use in advanced AEMWEs.Item Open Access Investigating 3-D effects on flashing cryogenic jets with highly resolved LES(2023) Gärtner, Jan Wilhelm; Kronenburg, Andreas; Rees, Andreas; Oschwald, MichaelFor the development of upper stage rocket engines with laser ignition, the transition of oxidizer and fuel from the pure cryogenic liquid streams to an ignitable mixture needs to be better understood. Due to the near vacuum conditions that are present at high altitudes and in space, the injected fuel rapidly atomizes in a so-called flash boiling process. To investigate the behavior of flashing cryogenic jets under the relevant conditions, experiments of liquid nitrogen have been performed at the DLR Lampoldshausen. The experiments are accompanied by a series of computer simulations and here we use a highly resolved LES to identify 3D effects and to better interpret results from the experiments and existing 2D RANS. It is observed that the vapor generation inside the injector and the evolution of the spray in the combustion chamber differ significantly between the two simulation types due to missing 3D effects and the difference in resolution of turbulent structures. Still, the observed 3D spray dynamics suggest a suitable location for laser ignition that could be found in regions of relative low velocity and therefore expected low strain rates. Further, measured droplet velocities are compared to the velocities of notional Lagrangian particles with similar inertia as the measured droplets. Good agreement between experiments and simulations exists and strong correlation between droplet size and velocity can be demonstrated.Item Open Access Development of an uncertainty quantification predictive chemical reaction model for syngas combustion(2017) Slavinskaya, Nadezda; Abbasi, Mehdi; Starcke, Jan Hendrik; Whitside, Ryan; Mirzayeva, Aziza; Riedel, Uwe; Li, Wenyu; Oreluk, Jim; Hegde, Arun; Packard, Andrew; Frenklach, Michael; Gerasimov, G. Ya.; Shatalov, OlegAn automated data-centric infrastructure, Process Informatics Model (PrIMe), was applied to validation and optimization of a syngas combustion model. The Bound-to-Bound Data Collaboration (B2BDC) module of PrIMe was employed to discover the limits of parameter modifications based on uncertainty quantification (UQ) and consistency analysis of the model−data system and experimental data, including shock-tube ignition delay times and laminar flame speeds. Existing syngas reaction models are reviewed, and the selected kinetic data are described in detail. Empirical rules were developed and applied to evaluate the uncertainty bounds of the literature experimental data. The initial H2/CO reaction model, assembled from 73 reactions and 17 species, was subjected to a B2BDC analysis. For this purpose, a dataset was constructed that included a total of 167 experimental targets and 55 active model parameters. Consistency analysis of the composed dataset revealed disagreement between models and data. Further analysis suggested that removing 45 experimental targets, 8 of which were self-inconsistent, would lead to a consistent dataset. This dataset was subjected to a correlation analysis, which highlights possible directions for parameter modification and model improvement. Additionally, several methods of parameter optimization were applied, some of them unique to the B2BDC framework. The optimized models demonstrated improved agreement with experiments compared to the initially assembled model, and their predictions for experiments not included in the initial dataset (i.e., a blind prediction) were investigated. The results demonstrate benefits of applying the B2BDC methodology for developing predictive kinetic models.Item Open Access Acoustic and aerodynamic evaluation of DLR small-scale rotor configurations within GARTEUR AG26(2024) Yin, Jianping; De Gregorio, Fabrizio; Rossignol, K.-S.; Rottmann, Lukas; Ceglia, Giuseppe; Reboul, Gabriel; Barakos, G.; Qiao, G.; Muth, Moritz; Keßler, Manuel; Visingardi, Antonio; Barbarino, Mattia; Petrosino, Francesco; Zanotti, Alex; Oberti, N.; Savino, Alberto; Bernardini, G.; Poggi, C.; Abergo, L.; Caccia, Francesco; Guardone, Alberto; Testa, C.; Zaghi, S.This paper presents the activities performed in the GARTEUR Action Group HC/AG-26 to study the acoustic and aerodynamic characteristics of small rotor configurations, including the influence of the rotor-rotor interactions. This paper will focus on comparisons between numerical activities and wind tunnel results on a small rotor provided by DLR. The wind tunnel models included a Rotor/Rotor/Pylon in isolated, tandem and coaxial configuration. The wind tunnel experiments for acoustics were performed in DLR’s Acoustic Wind Tunnel Braunschweig (AWB) and PIV test were performed in CIRA within a joint CIRA/DLR test program. For simulations, the numerical approaches from each partner are applied. The aerodynamic simulations necessary for the aeroacoustic predictions are conducted with various fidelity numerical methods, varying from lifting line to CFD. The acoustic values on the microphone positions are evaluated using Ffowcs Williams/Hawking (FW-H) formulation by all partners. The acoustic and aerodynamic predictions are compared to test data, including performance, PIV and acoustic directivity.Item Open Access Intensification of alkaline electrolyzer with improved two‑phase flow(2025) Egert, Franz; Ullmer, Dirk; Marx, Sven; Taghizadeh, Ehsan; Morawietz, Tobias; Gerle, Martina; Le, Thi Anh; Campo Schneider, Lucia Paula; Biswas, Indro Shubir; Wirz, Richard E.; Spieth, Philipp; Marquard‐Möllenstedt, Tonja; Brinner, Andreas; Faccio, Ricardo; Fernández‐Werner, Luciana; Esteves, Martín; Razmjooei, Fatemeh; Ansar, Syed AsifGreen hydrogen produced through water electrolysis offers a promising pathway to global decarbonization. Among various electrolyzers, alkaline water electrolysis (AWE) is the most established and commercially mature. To reduce the cost of hydrogen production from AWE, it is crucial to increase operational current density while maintaining or lowering voltage to increase hydrogen yield and reduce energy consumption. Such efforts are focused on reducing the ohmic resistance at high current densities through the implementation of alkaline membranes. However, this work underlines that the ohmic resistance at high current densities is also influenced by the losses associated with the evolution of bubbles at the electrode surface and two‐phase mass transfer. This is shown by investigating the impact of tortuosity and bubble point of porous electrodes on AWE performance. Low‐tortuosity porous nickel electrodes are fabricated and analyzed for their ability to reduce capillary pressure and bubble point, resulting in lower energy losses and improved efficiency. The cell reaches an industrially appealing relevant current density of 2 A cm -2 at ≈2 V. Besides test in single cells, the advantageous effect of these low tortuosity porous nickel electrodes are also validated in a kW‐class AWE stack, confirming their effectiveness in enhancing overall system performance.