Aerosolausbreitung in der DO-728-Passagierkabine. - In: Luft- und Raumfahrt, ISSN 0173-6264, Bd. 42 (2021), 2, S. 20-23
Am Deutschen Zentrum für Luft- und Raumfahrt in Göttingen wird am Institut für Aerodynamik und Strömungstechnik mit modernsten numerischen und experimentellen Methoden die Ausbreitung von Aerosolen in Flugzeugkabinen ausgehend von einer ausgewählten Quellposition untersucht. Ziele der vorliegenden Studie sind einerseits die experimentelle Bestimmung des Aerosoltransports, um die Grundlagen für die weitere Analyse möglicher Ansteckungen für Mediziner und Virologen zu legen, und andererseits durch numerische Studien das Potential alternativer Belüftungskonzepte aufzuzeigen. Mithilfe eines Aerosolausatmenden thermischen Menschmodells wurde experimentell die Ausbreitung von Aerosolen in dessen naher Umgebung bei klassischer Mischlüftung, d.h. die frische Luft wird im Deckenbereich zugeführt, nachgewiesen. Bereits in einer Entfernung von zwei Reihen beträgt die gemittelte Aerosolkonzentration weniger als 0.1 %. Innerhalb einer Reihe und insbesondere auf einer Gangseite findet dagegen ein erhöhter Aerosoltransport statt, was auch in den numerischen Strömungssimulationen bestätigt wird. Hohe Luftwechselraten und eine gerichtete Strömung verhindern, dass eine Ausbreitung der Aerosole über größere Entfernungen hinweg stattfindet. Wie in [5] dargestellt ist, reicht das derzeitige etablierte wissenschaftliche Verständnis der SARS-CoV-2-Übertragungsdynamik nicht aus, um aus den im Folgenden diskutierten Messungen des Aerosoltransports ein definitives SARS-CoV-2-Übertragungsrisiko zu berechnen. In den numerischen Studien wird nachgewiesen, dass Änderungen in den durch das Belüftungssystem induzierten Luftströmen in der Passagierkabine einen großen Einfluss auf die Aerosolverteilung haben. Es wird gezeigt, dass eine Belüftung nach dem Prinzip der bodenseitigen Verdrängungslüftung sowohl die räumliche Ausbreitung der Aerosole reduziert als auch die Verunreinigungsausfuhreffizienz deutlich steigern kann: nach 90 s sind nur noch 16 % der Partikel in der Kabinenluft.
Aerodynamic characterization of a full-scale compact car exposed to transient crosswind. - In: SAE International journal of passenger cars, ISSN 1946-4002, Bd. 14 (2021), 1, 06-14-01-0001P1-18
The transient surface pressure over a full-scale, operational compact automotive vehicle - a Volkswagen Golf 7 - exposed to transient crosswinds with relative yaw angles of β = 22-45˚ has been characterized. Experiments were performed at the BMW side-wind facility in Aschheim, Germany. Measurements of the incoming flow in front of the car were taken with eleven five-hole dynamic pressure probes, and separately, time-resolved surface pressure measurements at 188 locations were performed. Unsteady characteristics (not able to be identified in quasi-steady modelling) have been identified: the flow in separated regions on the vehicle's leeward side takes longer to develop than at the windward side, and spatially, the vehicle experiences local crosswind as it gradually enters the crosswind. The total effects of these localized unsteady pressure characteristics have also been predicted to affect the vehicle globally, with the evaluation of the transient forces and moments - through pressure integration - exhibiting unsteady characteristics of overshoots, undershoots, and temporal lag; relative to steady crosswind. These results provide new insight into both the characteristics and the causes of the unsteady crosswind response of a real, operational vehicle operating in real-world conditions. This insight can be used in the design of future vehicles to make them less sensitive to unsteady gusts. Further these results can be used to develop and validate numerical and reduced-scale experimental methods that can test and assess new vehicle geometry designs during the early stages of vehicle development.
https://doi.org/10.4271/06-14-01-0001
On the simulation of a heavy vehicle wake in OpenFOAM with real-world data. - In: New results in numerical and experimental fluid mechanics XIII, (2021), S. 504-513
Two computational approaches are taken to characterize the drag of a car driven behind a heavy vehicle under real conditions. The on-road approach uses velocity measurements, obtained from an array of static five-hole probes, to construct on-flow boundary conditions replicating the atmospheric dynamics encountered during an on-road measurement. The wind tunnel approach uses an oscillating flap system to control flow time and length scales upstream of a wind tunnel model. The amplitude and frequency of the flap motion is calibrated to reproduce length and time scales at on-road conditions under respective Reynolds and Strouhal number scaling. These approaches are evaluated against experimental measurements using Computational Fluid Dynamics (CFD) and demonstrates that they reproduce the aerodynamic drag and a significant part of the measured onflow condition for the car.
Characterization of a mixed convection cell designed for phase transition studies in moist air. - In: New results in numerical and experimental fluid mechanics XIII, (2021), S. 483-493
A detailed description of an experimental set-up designed for upcoming investigations of latent and sensible heat transfer in a cuboid sample with air in- and outlets is given. The container is heated at the rear and cooled at the transparent front wall. Temperature measurements reveal that both sides exhibit a mean temperature deviation below 2% relative to the temperature difference between the mean plate temperature and the ambient temperature. This is a suitable temperature distribution for such measurements. Tomographic particle image velocimetry covering the entire volume of the mixed convection cell exhibits a large-scale circulation due to forced convection with a buoyancy-induced flow close to the temperature controlled surfaces. Forced convection origins from a flow between the inlet and the outlet channel with a mean deviation of 1% from the mean velocity and a maximum absolute deviation of 0.04 m/s. Measurements were performed for Reynolds numbers ranging from 300<Re<2000 and Grashof numbers Gr<1.2×10^8. A representative flow field obtained at Re=620 and Gr=1.1×10^8 is presented as an example.
Modelling of heat transfer for droplet condensation in mixed convective duct flow. - In: New results in numerical and experimental fluid mechanics XIII, (2021), S. 461-471
Temperature and humidity measurements are conducted in mixed convective humid-air duct flow with condensation. The latent and total heat transfer during the experiment are determined through the thermal balance for inlet temperatures from 27.5 ˚C to 35.5 ˚C, relative humidities from 30% to 55% and at four Reynolds numbers (2000-8000). The experimental results are compared with a heat transfer model from the literature. Adjusted in terms of the geometry and surface properties, the model shows partial agreement for the cases with forced convection but has to be further adjusted regarding the influence of thermal convection.
Bi-stability detection in the flow around a sphere by means of experiments and lattice Boltzmann simulations. - In: New results in numerical and experimental fluid mechanics XIII, (2021), S. 441-450
With the aim to detect bi-stability in the highly separated flow around a sphere mounted on a cross-stream rod, wind tunnel measurements and numerical simulations with a Lattice Boltzmann method (LBM) are performed and compared. In both, LBM simulation and experiment, a bi-stable flow behaviour is detected at a Reynolds number of Re=10^5 based on the sphere diameter, the inflow velocity and the kinematic viscosity, whereas such behaviour is absent at Reynolds numbers as high as Re=3×10^5. The bi-stable behaviour detected in the time series of the aerodynamic side force acting on the sphere for Re=10^5 is reflected by a bi-modal probability density function. For Re=3×10^5, on the contrary, the probability density function is nearly Gaussian. Further, in agreement with the experiment, two counter-rotating vortex tubes originating from the intersection of the leeward and cross-stream rod-ward side of the sphere are generated.
Aerodynamic characterisation of a compact car driving behind a heavy vehicle. - In: New results in numerical and experimental fluid mechanics XIII, (2021), S. 514-524
The transient incoming flow a compact car experiences whilst driving 10 m - 100 m behind a heavy vehicle on a runway has been characterised. The incoming flow was measured using a 2D array of 11 five-hole probes mounted 1 m in front of an operational, full-scale compact car. Additionally, 188 surface pressure taps were used to measure the effect of the incoming flow conditions on the compact car. The experiments were performed under ideal conditions on a 2.9 km long runway in Faßberg near the DLR in Trauen, Germany.
Time-resolved high-density particle tracking velocimetry of turbulent Rayleigh-Bénard convection in a cubic sample. - In: Turbulence and interactions, (2021), S. 176-182
A newly developed high-density particle tracking velocimetry (HD-PTV) technique is introduced and validated on a synthetic data set. Further, Lagrangian velocities in turbulent Rayleigh-Bénard Convection (RBC) are determined based on particle images measured in a cubic sample filled with water with a Prandtl number Pr=6.9 and a Rayleigh number of Ra=1.0⋅10^10. It is shown that the new technique allows to resolve not only a three-dimensional (3D) large-scale circulation in a diagonal plane of the sample but also the secondary flow structures developing in the corners of the perpendicular plane.
Effect of very-large-scale motions on one- and two-point statistics in turbulent pipe flow investigated by direct numerical simulations. - In: Turbulence and interactions, (2021), S. 117-122
Very-large-scale motions appear in the bulk region of turbulent pipe flow. They become increasingly energetic with the Reynolds number and interact with the near-wall turbulence. These structures appear either in the shape of positive (high-speed) or negative (low-speed) streamwise velocity fluctuation. The impact of the sign of the structures on the pipe flow turbulence is analysed in this study by means of conditionally averaged one- and two-point statistics, using data from direct numerical simulations of turbulent pipe flow in a flow domain of length L=42R and friction Reynolds numbers of 180≤Reτ≤1500. Conditionally averaged two-point velocity correlations reveal that low-speed motions are longer and more energetic than their high-speed counterparts. The latter are predominately responsible for the Reynolds number dependency of turbulence statistics in the vicinity of the wall, which is in good agreement with observations of the so-called amplitude modulation in wall-bounded turbulence.
Optimierung von Luftauslass- und Kanalgeometrien mit adjungierten Verfahren. - Ilmenau : Universitätsbibliothek, 2021. - 1 Online-Ressource (xxi, 166 Seiten)
Technische Universität Ilmenau, Dissertation 2021
Die Auslegung von Belüftungssystemen in Flugzeugen, Zügen und Autos ist in erster Linie von der Erfahrung und dem Fachwissen der Entwicklungsingenieure sowie intensiven Tests abhängig. Mit numerischen Optimierungsverfahren ist es jedoch möglich, die Systeme noch weiter zu verbessern. In der vorliegenden Arbeit werde ich eine Prozesskette entwickeln, die mit Hilfe der adjungierten Formoptimierung auf Grundlage numerischer Strömungsmechanik den Kabinenluftauslass des Dornier 728 Flugzeugs optimiert. Dabei soll in der Netzverformung eine hohe Zahl an Freiheitsgraden verwendet werden, die durch die adjungierte Formoptimierung zur Verfügung steht. Zusätzlich wird die vorgestellte Prozesskette auf ein vektrowertiges Optimierungsproblem angewendet, wobei die Pareto-Front zweier Zielfunktionen für den Kabinenluftauslass bestimmt wird. Laut Stand der Technik wird für solche Problemstellungen die Methode der gewichteten Summe angewendet. Diese bedeutet zugleich einen enormen Rechenaufwand, wenn man komplexe Geometrien untersucht. Um diesen Aufwand zu reduzieren, präsentiere ich ein Verfahren, bei dem die Sensitivitätsfelder aus skalarwertigen Optimierungsproblemen kombiniert werden. Die Variation dieser Skalierungsfaktoren erfolgt mit einem genetischen Algorithmus. Im nächsten Schritt wird das Problem noch einmal umformuliert und die Variation der Wichtungsfaktoren wird mit einem E-Schranken-Verfahren untersucht. Im Vergleich zur Kombination der Zielfunktionen liefert das präsentierte Verfahren bei gleichbleibender Rechenzeit eine Verbesserung der Zielfunktion von ca. 70% bzw. ca. 40% Verbesserung bei einer Einsparung von 50% der Rechenzeit. Zusätzlich zeigt auch die bestimmte Pareto-Front geringere Werte für die untersuchten Zielfunktionen.
https://nbn-resolving.org/urn:nbn:de:gbv:ilm1-2021000301