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State Estimation and Linear Discrete Model Predictive Control for the Hydration Process in a Lime-Based Thermochemical Energy Storage System
No full textConcluding the Development of C/C-SiC Based Thermal Protection Material With Random Porosity for Hypersonic Transition Suppression
No full textThe present work concludes the experimental and numerical efforts to develop a C/C-SiC based material for use as ultrasonically absorptive thermal protection to passively control hypersonic boundary layer transition. The study covers the design strategy including the linear stability analysis of the flow field at the test condition of interest, the homogeneous absorber theory for an initial absorber layout, the material design, the acoustic characterization of the C/C-SiC samples resulting from different manufacturing processes, the final tests in the High Enthalpy Shock Tunnel Göttingen (HEG) and the numerical prediction of the observed transition delay. The wind tunnel tests to validate the design approach are conducted on a 7 degree half angle cone with a large C/C-SiC insert tested at Mach 7.4 in the shock tunnel HEG. The change of second mode instability growth and its effect on the transition location are investigated by means of high speed Schlieren visualization and surface mounted transducers assessing the surface heat flux. Strong boundary layer transition delay on the porous surface was observed
Transitional Phenomena on an Elliptic Profile
No full textElliptic profiles have been the subject of fundamental flow research as “elliptic cylinders” since several decades, including the study of boundary-layer separation and transition. In recent times, elliptic profiles have become relevant also for practical applications, such as canard rotor/wing aircraft and hydrokinetic energy harvesting technologies. In these cases, they are operated at moderate Reynolds numbers, at which their fluid dynamic behavior is strongly influenced by boundary-layer transition and separation. Therefore, information on these crucial phenomena is of fundamental importance for the experimental evaluation of the aero/hydrodynamic performance of elliptic profiles and the validation and improvement of the numerical prediction of the involved fluid dynamics.
The transition of the boundary layer developing on an elliptic profile with 16\% relative thickness is the focus of the present work. The experiments were conducted in the Large Watertunnel of the Technical University of Braunschweig (GWB) on a two-dimensional model with a chord length of 0.2 m. The model upper surface was equipped with a Temperature-Sensitive Paint (TSP) for the global, non-intrusive, time-resolved measurement of the surface temperature distribution, and thus of boundary-layer transition. The TSP data were acquired over a mid-span region of approx. 0.2 m x 0.3 m at a frequency of 1 kHz. The model was also equipped with a row of pressure taps to measure the surface pressure distribution.
The experiments were performed at two chord Reynolds numbers (Re = 2.5 and 5.0 x 10^5) for a wide range of angles-of-attack (-4° <= AoA <= 30°), thus enabling the study of the boundary-layer evolution for a wide range of stability situations. Two exemplary TSP results show the intermittent character of the transition front in the presence of a weak adverse pressure gradient and transition occurring over a laminar separation bubble close to the leading edge, as induced by a stronger adverse pressure gradient. Turbulent spots were identified in both cases.
The final contribution will provide the temporal development of the transitional phenomena and a detailed analysis of the transition evolution for the examined flow conditions
Improving TanDEM-X Data for the Reduction of Uncertainties when Measuring Snow and Ice Dynamics
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Experimental Study of the Instability Amplitude Effect on Critical Step Heights in Crossflow-Dominated Transition
No full textAccurate tolerance criteria for two-dimensional surface irregularities such as steps and gaps are important for future laminar wing designs. Research into step height tolerances is more advanced for two-dimensional than for three-dimensional boundary layers. At DLR, the SPECTRA (Swept flat PlatE Crossflow TRAnsition) configuration is used to study crossflow-dominated laminar-turbulent transition. Recently, the configuration has been refined concerning its experimental capabilities. A new motorized hot-wire positioning system was developed and a global transition-detection system based on temperature-sensitive paint (TSP) was integrated. The configuration can now be used for investigations in the DNW-NWB wind tunnel in addition to the DLR-1MG wind tunnel. In Fig. 1, a cross-section of the SPECTRA configuration is shown with an exaggerated forward-facing step at the chordwise location xc = 150 mm. At that location, the flat plate is split into two segments. The nose segment can be shifted vertically relative to the other segment to produce forward- or backward-facing steps. The newest addition to SPECTRA is a system for motorized adjustment of this vertical shift and therefore the step height, inspired by the system used by Duncan et al.. Eppink investigated forward-facing steps and demonstrated an effect of the amplitude of stationary crossflow instabilities (CFI) on the criticality of a fixed step height. To study this effect in more detail, the CFI amplitude was varied systematically in parallel to a systematic variation of forward-facing step heights in SPECTRA experiments in the 1MG wind tunnel. The initial CFI amplitude and therefore the amplitude at the step location was varied by changing the diameter and chordwise location of discrete roughness elements (DRE) in a spanwise-equidistant array with constant spanwise spacing. The amplitude of the excited CFI was quantified with hot-wire measurements in the linear regime of their development for each roughness configuration. LST analysis was used to derive the CFI amplitude at the average chordwise excitation location. For each test case, the spanwise-averaged transition location was derived from TSP measurements. With increasing step height, the transition location eventually moves rapidly upstream towards the step location. This movement marks the "critical" step height and step Reynolds number. In Fig. 2, the critical step Reynolds number is shown to decrease approximately linearly with the initial CFI amplitude a0. For a given setup, the latter determines the CFI amplitude at the step location, which is most likely crucial for the onset of step criticality. In addition, it is not yet fully understood how the properties of the pressure distribution affect the critical step height in crossflow-dominated laminar-turbulent transition. In SPECTRA investigations in DNW-NWB, the criticality of forward-facing steps was investigated under the influence of six different pressure distributions, created by a variation of the angle of attack of the displacement body. The experimental results (shown in Fig. 3) have been interpreted together with results from a stability analysis of the respective base flows without a step. In the presentation and the full paper, a connection between the results from the variation of the pressure distribution and the isolated variation of the CFI amplitude will be demonstrated
Sensitivity of Near-Infrared Bands to Cloud Phase: An Assessment Using Dual-View Satellite Measurements
No full textAccurate cloud phase classification in the near-infrared is challenging due to the overlapping radiative properties of water, ice, and mixed-phase clouds.
This study presents a new composite Phase Classification Index (PCINIR,DV) for near-infrared satellite measurements in a dual-viewing geometry. The index is defined as the product of two physically derived components: (1) a spectral ratio of top-of-atmosphere radiances at 1.61 μm and 2.25 μm, which exploits the differences in absorption between water and ice, and (2) a directional ratio of 0.87 μm radiances from oblique and nadir views, which are influenced by scattering. Theoretical simulations using the SCIATRAN radiative transfer model demonstrate that the PCINIR,DV effectively distinguishes between pure water and ice clouds, enabling mixed-phase clouds to be identified. Sensitivities are analyzed for ranges of particle sizes, ice fractions, and surface types. Theoretical results show that water clouds, excluding thin clouds over snow surfaces, exhibit high PCINIR,DV values (above 3.5), ice clouds yield low values (below 2.75), and intermediate values correspond to mixed-phase clouds. Validation of PCINIR,DV derived from the Sea and Land Surface Temperature Radiometer (SLSTR) dual-view observations (onboard Sentinel-3A) against CloudSat-CALIPSO phase classifications confirms its applicability, yielding 86% classification accuracy, including over 63% for mixed-phase clouds. The results demonstrate that PCINIR,DV provides a robust physical framework for dual-view satellite missions, which aim to measure the cloud phase
Buckling prediction of cylindrical shells by vibration considering stochastic modelling, combined loading and industrial-scale validation
Full text linkThe Vibration-Correlation Technique (VCT) has established itself as a reliable method to predict the buckling loads of cylindrical shells under compression. However, the method was not considered mature enough to deploy in industrial experimental campaigns, owing to several aspects that needed further investigation. In this dissertation, some of these aspects are investigated, starting with the method's sensitivity to key measurement parameters. Then, the influence of various amplitudes of shape and loading imperfections on the robustness of the method is assessed. Afterwards, the influence of applying additional bending, shear, and/or torsion loads on the VCT estimation of the axial buckling load was investigated. Lastly, the experimental results of a cylindrical shell representative of a real-scale launcher structure, tested under two bending-compression load cases, are presented
Exemplary calculations for necessary traffic changes through behavioral changes in order to achieve the EU emission limits using the example of Potsdam
No full textClimate change, exceedances of pollutant thresholds, growing cities and the resulting increased traffic load are still global challenges. Although the German Environment Agency reports that in 2024, for the first time, the nitrogen dioxide loads of all measurement stations remained within the threshold values, improvements are still necessary until the planned tightening of the threshold values in 2030. In the MaaS L.A.B.S. project, a small group of test subjects in Potsdam near Berlin was tested to see what motivates people to switch to public transportation. A tracking app with incentive options was used for this purpose [Sauerländer-Biebl et al., 2023]. Motivated by the feedback from the test subjects that even the knowledge of how much CO2 they had saved by taking an alternative means of transportation (public transport, bicycle or on foot) was enough to make them give up their car. This leads to the question how much more non-car tips does it take to measure a change in emission output. By using statistic data, it can be estimated how many more people need to be motivated to switch to reach the EU threshold values, or how much more time residents would have to spare if they did not drive a car and used the current alternatives