Universität Stuttgart

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Author: search.filters.author.Eberhart, MartinSubject: search.filters.subject.620

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    Assessment of high enthalpy flow conditions for re-entry aerothermodynamics in the plasma wind tunnel facilities at IRS
    (2021) Loehle, Stefan; Zander, Fabian; Eberhart, Martin; Hermann, Tobias; Meindl, Arne; Massuti-Ballester, Bartomeu; Leiser, David; Hufgard, Fabian; Pagan, Adam S.; Herdrich, Georg; Fasoulas, Stefanos
    This article presents the full operational experimental capabilities of the plasma wind tunnel facilities at the Institute of Space Systems at the University of Stuttgart. The simulation of the aerothermodynamic environment experienced by vehicles entering the atmosphere of Earth is attempted using three different facilities. Utilizing the three different facilities, the recent improvements enable a unique range of flow conditions in relation to other known facilities. Recent performance optimisations are highlighted in this article. Based on the experimental conditions demonstrated a corresponding flight scenario is derived using a ground-to-flight extrapolation approach based on local mass-specific enthalpy, total pressure and boundary layer edge velocity gradient. This shows that the three facilities cover the challenging parts of the aerothermodynamics along the entry trajectory from Low Earth Orbit. Furthermore, the more challenging conditions arising during interplanetary return at altitudes above 70 km are as well covered.
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    3-D visualization of transparent fluid flows from snapshot light field data
    (2021) Eberhart, Martin; Loehle, Stefan; Offenhäuser, Philipp
    This paper presents the use of light field data, recorded in a snapshot from a single plenoptic camera, for 3-D visualization of transparent fluid flows. We demonstrate the transfer of light field deconvolution, a method so far used only in microscopy, to macroscopic scales with a photographic setup. This technique is suitable for optically thin media without any additional particles or tracers and allows volumetric investigation of non-stationary flows with a simple single camera setup. An experimental technique for the determination of the shift-variant point spread functions is presented, which is a key for applications using a photographic optical system. The paper shows results from different test cases with increasing complexity. Reconstruction of the 3-D positions of randomly distributed light points demonstrates the achievable high accuracy of the technique. Gas flames and droplets of a fluorescent liquid show the feasibility of the proposed method for the visualization of transparent, luminous flows. The visualizations exhibit high quality and resolution in low-contrast flows, where standard plenoptic software based on computer vision fails. Axial resolution depends on the data and is about an order of magnitude lower than the lateral resolution for simple point objects. The technique also allows the time-resolved analysis of flow structures and the generation of 3D3C-velocity fields from a sequence of exposures.
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    Festelektrolytsensoren zur Messung von atomarem Sauerstoff auf Forschungsraketen
    (2019) Eberhart, Martin; Fasoulas, Stefanos (Prof. Dr.-Ing.)
    Die Dissertation behandelt die Untersuchung, Entwicklung und Anwendung von amperometrischen Festelektrolytsensoren zur lokal aufgelösten Messung der Teilchendichten von atomarem und molekularem Sauerstoff auf Höhenforschungsraketen. Die Teilchendichten dieser Spezies sind für die Physik der Atmosphäre von großer Bedeutung und werden in Raketenexperimenten in der sogenannten MLT-Region im Höhenbereich zwischen 70 und 110 km bestimmt. Für die Kalibrierung der Sensoren auf atomaren Sauerstoff wird eine neue Methode entwickelt, die ein Massenspektrometer in Cross-Beam-Konfiguration als Referenzinstrument verwendet. Das transiente Verhalten der Sensoren wird in dieser Arbeit erstmalig sowohl numerisch als auch experimentell behandelt. Die Arbeit präsentiert die Ergebnisse der Messungen auf zwei Raketenflügen des Projekts WADIS.
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    Chemical heat derived from rocket-borne WADIS-2 experiment
    (2024) Grygalashvyly, Mykhaylo; Strelnikov, Boris; Strelnikova, Irina; Rapp, Markus; Lübken, Franz-Josef; Schütt, Corinna; Stephan, Claudia; Eberhart, Martin; Löhle, Stefan; Fasoulas, Stefanos
    Chemical heating rates were derived from three of the most significant reactions based on the analysis of common volume rocket-borne measurements of temperature, atomic oxygen densities, and neutral air densities. This is one of the first instances of the retrieval of nighttime chemical heat through the utilization of non-emissive observations of atomic oxygen concentrations, obtained through in situ measurements, performed at the Andøya Space Center (69°N, 16°E) at 01:44:00 UTC on 5 March 2015. Furthermore, we determine the heating efficiency for one of the most significant reactions of atomic hydrogen with ozone and illustrate the methodology for such calculations based on known atomic oxygen and temperature. Subsequently, using ozone values obtained from satellite observations, we retrieved odd-hydrogens and total chemical heat. Finally, we compared the retrieved chemical heat with the heat from turbulent energy dissipation. Our findings reveal that the vertically averaged chemical heat is greater than the heat from turbulent energy dissipation throughout the entire mesopause region during nocturnal conditions. The heating rates of turbulent energy dissipation may exceed the chemical heating rates only in narrow peaks, several hundred meters wide.