Narrative, Luck, and Ethics: The Role of Chance in Ethical Encounters, in Literature and Real Life Experiences

Presented to the WMU Center for the Study of Ethics in Society - March 9, 1993

Scaling Laws for the Aeroacoustics of High Speed Trains

The present study focuses on the scaling of the main aeroacoustic sound sources of a high speed train. The investigations are carried out by measuring in a wind tunnel by means of microphone array technique. The experiments using a 1:25 Inter City Express 3 model were conducted in two different wind tunnels: The Aeroacoustic Wind tunnel (AWB) of the German Aerospace Center (DLR) in Brunswick, which provides nearly perfect acoustically conditions, and in the Cryogenic wind tunnel (DNW-KKK) of the DNW (German - Dutch wind tunnels) in Cologne, which allows measurements at higher Reynolds numbers. Two different sources of sound with different characteristics are identified from the measurements in the AWB at Reynolds numbers up to Re = 0.46 mio: The aeroacoustic noise from the bogie section is dominant for frequencies f < 6 kHz and can be characterised by cavity mode excitation. The shape of the spectrum is not velocity dependent within the investigated velocity range. The pantograph is the dominant source of sound above $f = 6$ kHz. It is more tonal noise and the frequency peaks show a strong velocity dependence. These two sources of sound demonstrate that it is not possible to formulate one scaling law for all sources of sound of a train. It is essential to treat every single source separately and to t-ake their characteristics into account. In order to investigate the noise generated at the bogies at higher Reynolds numbers up to 3.70 mio a second measurement campaign has been conducted in the cryogenic wind tunnel. By cooling down from T = 300 K to T = 100 K one changes the physical properties of the fluid and the Reynolds number increases by a factor of ~5. Besides, this wind tunnel admits to vary the Mach and Reynolds numbers independently. Drawback of this facility is that it is not optimised for aeroacoustic experiments and reflexions as well as the high background noise level can disturb the results. The Mach number is kept constant and a Reynolds number variation is realised by varying of the temperature. The first bogie shows only a weak Reynolds number dependence. The deviations are within the measurement accuracy. To go more into detail further investigations with an improved setup are planed

The Effect of Boundary Layer Control with Roughness Elements on the Wake Flow of Moving Train Models

Moving model experiments are used to investigate the flow around three different train geometries. Due to the difference in the Reynolds number, the flow might not be directly comparable to full-scale measurements. Boundary layer control is used to influence the flow around the train model and increase the boundary layer velocity. With view on the standards given by the Technical specification of Interoperability, the analysis of the wake shows increased maximum induced flow velocities at the specific standard measurement position

Gekoppelte aerodynamische und fahrdynamische Simulation zur Optimierung von Tunnelfahrten

Eingleisige Tunnelröhren auf Hochgeschwindigkeitsstrecken stellen aufgrund der kleinen Querschnittsfläche in Bezug auf den Luftwiderstand bei der Tunneldurch-fahrt, der entstehenden Drucklasten sowie der Abstrahlung von Mikrodruckwellen, welche Ursache des sogenannten Tunnelknalls sind, besondere Herausforderungen an die Planung und Dimensionierung des Bauwerks. Gegenwärtig werden die akusti-schen Umweltwirkungen durch bauliche Anpassungen wie Portalhauben, Quer-schnittsaufweitungen oder Entlüftungsschächte beeinflusst. Im vorliegenden Beitrag wird untersucht, in wieweit betriebliche Anpassungen der Fahrkennlinie des Zuges geeignet sind, die Tunnelaerodynamik und -akustik zu beeinflussen. Hierzu werden eine aerodynamische Simulation der Druckentwicklung innerhalb des Tunnels sowie eine fahrdynamische Simulation in einem iterativen Prozess gekoppelt, sodass wech-selseitige Abhängigkeiten von Fahrverhalten und Tunnelaerodynamik modelliert werden können. Die Methodik wird anhand eines Fallbeispiels auf Basis des Katzen-bergtunnels getestet und es wird gezeigt, dass durch die Reduktion der Tunnelein-fahrgeschwindigkeit sowohl die Umweltwirkung von Tunnelfahrten als auch die Energieeffizienz positiv beeinflusst werden können bei relativ moderaten Fahrzeitver-lusten

Insights Into The Acoustic Near And Far Field Based On Synchronized PIV And Microphone Measurements

The aim of this study is to detect and visualize the propagating sound waves emanating from a flow around different types of rods. For this purpose, synchronous Particle Image Velocimetry (PIV) and microphone measurements were performed in an aeroacoustic wind tunnel. The velocity fluctuations were recorded not only in the vicinity of the rods but also in several regions between the wake flow field and the far field microphone. By means of the correlation between velocity and pressure fluctuations, coherent structures within and outside the flow could be identified. In particular, the temporal and spatial development of these structures provides an insight into the sound generation mechanism and the transition between the acoustic near and far field. The results are compared with analytical and numerical solutions

On the Coverage of Dynamic Processes in Highly Separated Flows Using the Lattice Boltzmann Method

Ground vehicles are exposed to a vast variety of unsteady aerodynamic phenomena such as gusts. This is why the effect of gusts has been the focus of many studies, e.g. on cars in full scale (Schroeck et al., 2011), trains in full scale (Baker et al., 2004) as well as on simplified car models in wind tunnels (Ferrand, 2014). In order to gain better insight into the flow dynamics, Hemida and Krajnovic (2010) investigated the effect of ´cross winds on a generic train with different nose shapes using large-eddy simulations. Another unsteady effect that has recently gained interest is the multi-stability of the wake behind cars. In this context, Cadot et al. (2016) detected bi-stability in the lift forces acting on full-scale cars during wind tunnel testing. This bi-stability was further investigated in wind tunnel testing on simplified car models by Grandemange et al. (2013) and Pavia et al. (2018). Due to the highly transient behaviour of the flow, the existing numerical methods require revision concerning their capability of coping with the flow dynamics. For such investigations, the flow around a sphere is usually chosen as a setup, as it has been in the focus of aerodynamic research since the very beginning (Prandtl, 1914) and, thus, is the subject of many studies described in the literature. However, the flow around a sphere is an example of a fully separated flow, whose prediction poses a challenge to numerical investigations such as the DES study of Constantinescu and Squires (2004). The highly instationary dynamics in the wake of such a flow are described by hot-wire measurements (Achenbach, 1972) as well as by flow visualisation (Chrust et al., 2013). The latter clearly shows the development of hairpin vortices and the loss of planar symmetr

High-Speed Particle Image Velocimetry of the Flow around a Moving Train Model with Boundary Layer Control Elements

Trackside induced airflow velocities, also known as slipstream velocities, are an important criterion for the design of high-speed trains. The maximum permitted values are given by the Technical Specifications for Interoperability (TSI) and have to be checked in the approval process. For train manufactures it is of great interest to know in advance, how new train geometries would perform in TSI tests. The Reynolds number in moving model experiments is lower compared to full-scale. Especially the limited model length leads to a thinner boundary layer at the rear end. The hypothesis is, that the boundary layer rolls up to characteristic flow structures in the train wake, in which the maximum flow velocities can be observed. The idea is to enlarge the boundary layer using roughness elements at the train model head so that the ratio between the boundary layer thickness and the car width at the rear end is comparable to a full-scale train. This may lead to similar flow structures in the wake and better prediction accuracy for TSI tests. In this case, the design of the roughness elements is limited by the moving model rig. Small rectangular roughness shapes are used to get a sufficient effect on the boundary layer, while the elements are robust enough to withstand the high accelerating and decelerating forces during the test runs. For this investigation, High-Speed Particle Image Velocimetry (HS-PIV) measurements on an ICE3 train model have been realized in the moving model rig of the DLR in Göttingen, the so called tunnel simulation facility Göttingen (TSG). The flow velocities within the boundary layer are analysed in a plain parallel to the ground. The height of the plane corresponds to a test position in the EN standard (TSI). Three different shapes of roughness elements are tested. The boundary layer thickness and displacement thickness as well as the momentum thickness and the form factor are calculated along the train model. Conditional sampling is used to analyse the size and dynamics of the flow structures at the time of maximum velocity in the train wake behind the train. As expected, larger roughness elements increase the boundary layer thickness and lead to larger flow velocities in the boundary layer and in the wake flow structures. The boundary layer thickness, displacement thickness and momentum thickness are increased by using larger roughness especially when applied in the height close to the measuring plane. The roughness elements also cause high fluctuations in the form factors of the boundary layer. Behind the roughness elements, the form factors rapidly are approaching toward constant values. This indicates that the boundary layer, while growing slowly along the second half of the train model, has reached a state of equilibrium