FG Aerodynamik und Strömungslehre
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Influence of convex structured surfaces on turbulent channel flow at different channel heights
(2019)
Influence of the temperature-dependent viscosity on convective flow in the radial force field
(2017)
Instabilities with polyacrylamide solution in small and large aspect ratio Taylor-Couette systems
(2007)
Instabilities with polyacrylamide solution in small and large aspect ratio Taylor-Couette systems
(2007)
Instabilities with polyacrylamide solution in small and large aspect ratios Taylor-Couette systems
(2008)
Interacting inertial modes and their instability in a differentially rotating spherical gap flow
(2016)
Investigation of flow over bluff bodies with patterned surface using Laser-Doppler Anemometry
(2012)
Ziele des Vorhabens sind die Verbesserung der Messtechnik für tribologische Untersuchungen in der Kolbengruppe aus dem Vorläufervorhaben Kolbenring-Öltransport I und die Untersuchung von verschiedenen Betriebsbedingungen und Komponenten hinsichtlich ihres Einflusses auf den Ölhaushalt. Der Fokus liegt auf der verbesserten Auflösung der Schmierfilmdickenmessung und der Ringstoßlagen. Mit der erweiterten Kapillar- und Lichtleiterkonfiguration werden neue Öltransportvorgänge entlang des Kolbenringpakets mittels Tracerinjektion und simultaner LiF-Messung beobachtet. Das methodische Vorgehen bei der optischen Analyse des Kapillarfüllungsgrades wird an einem Labor-Druckprüfstand weiterentwickelt.
Des Weiteren werden komplexe Simulationsmodelle erstellt, mit denen die Kolbensekundär-bewegung, die Kolbenringbewegung, die Gasströmung im Ringpaket und der Öltransport im Ringpaket geklärt werden können. Die Kolbensekundärbewegungsrechnung basiert auf einer FEM-Diskretisierung die aus CAD-Modellen sämtlicher Bauteile abgeleitet ist. Die dreidimensionale Berechnung der Kolbenringbewegung erfolgt unter Berücksichtigung dynamisch wirkender Kräfte aus der Bewegung, der Ringreibung, dem Gasdruck und den Zwischenring- drücken. Die Elastizität der Ringe wird berücksichtigt, so dass Biegung, Torsion und damit auch das Twisten abgebildet werden können. Nut- und Ringgeometrie sowie thermisch bedingte Verzüge fließen ebenfalls in die Berechnung mit ein. Als Ergebnisgrößen stehen neben den Ringbewegungen und -lagen auch die Gasströmungen und -drücke, Schmierfilmhöhen und Verlustleistungen zur Verfügung.
Laboratory experiments and numerical simulations of inertial waves in a rotating spherical shell
(2016)
LDA-Messungen zur Untersuchung barokliner Instabilitäten, Lasermethoden in der Strömungsmesstechnik
(2002)
Linear stability analysis of the convective flow in a spherical gap with rotating inner surface
(2020)
Time periodic variation of the rotation rate of an annulus induces in supercritical regime an unstable Stokes boundary layer over the cylinder side walls, generating
Görtler vortices in a portion of a libration cycle as a discrete event. Numerical results show that these vortices propagate into the fluid bulk and generate an azimuthal
mean flow. Direct numerical simulations of the fluid flow in an annular container with librating outer (inner) cylinder side wall and Reynolds-averaged Navier–Stokes
(RANS) equations as diagnostic equations are used to investigate generation mechanism of the retrograde (prograde) azimuthal mean flow in the bulk. First, we explain, phenomenologically, how absolute angular momentum of the bulk flow is mixed and changed due to the propagation of the Görtler vortices, causing a new vortex
of basin size. Then we investigate the RANS equations for intermediate time scale of the development of the Görtler vortices and for long time scale of the order of
several libration periods. The former exhibits sign selection of the azimuthal mean flow. Investigating the latter, we predict that the azimuthal mean flow is proportional to the libration amplitude squared and to the inverse square root of the Ekman number and libration frequency and then confirms this using the numerical data.
Additionally, presence of an upscale cascade of energy is shown, using the kinetic energy budget of fluctuating flow.
Laboratory experiments with a rotating cylindrical annulus arereported that reveal a prograde jet, which is adjacent to a (longitu-dinally) librating inner straight cylindrical wall. Here, wall libration isrealised as a time-harmonic modulation of the inner cylinder’s rota-tion rate. The outer cylindrical wall and bottom and top lids rotatewith constant angular velocity. The main purpose of our study is tocontribute to a qualitative and quantitative understanding of non-linearities that are present in oscillating, but centrifugally stable,vertical boundary layers frequently encountered in rotating wall-bounded flows. We consider a problem that is in a sense comple-mentary to that of previous works that focused on oscillating Ekmanlayers but neglected the vertical Stokes−Stewartson layers. A sim-ple analytical model is proposed that is able to predict the magni-tude and spatial structure of the emerging prograde near-wall jet interms of nonlinearity inherent in the inner cylinder’s boundary layerdynamics.
The main focus of the project series “Piston Ring Oil Transport” is the investigation of the tribological conditions in the piston assembly. Within the first part of the project, a 0.5-l single-cylinder research engine was built up [1, 2], which is equipped with numerous sensors to measure the tribological circumstances. In the second project part [3] presented here, additional simulation models are developed, which gain accuracy compared to the recorded measurement data and contribute significantly to an understanding of the oil supply at the piston assembly.
Die Projektreihe Kolbenring-Öltransport dient der Untersuchung der tribologischen Zustände in der Kolbengruppe. Dabei wurde im ersten Projektabschnitt ein 0,5-l-Einzylinder-Forschungsmotor aufgebaut, der mit zahlreichen Sensoren ausgerüstet ist, um diese Zustände messtechnisch zu erfassen. Im zweiten, hier ausschnittsweise vorgestellten Projektabschnitt wurden zusätzliche Simulationsmodelle implementiert, die durch Abgleich mit den aufgezeichneten Messdaten an Genauigkeit gewinnen und zum Verständnis des Ölhaushalts in der Kolbengruppe erheblich beitragen.
Mixing and overshooting in surface convection zones of DA white dwarfs: First results from ANTARES
(2018)
Modified Optical and Thermal Anemometers for Laminar and Turbulent Boundary Layers Investigation
(2005)
The large-scale flows of the oceans and the atmosphere are driven by a non-uniform surface heating over latitude, and rotation. For many years scientists try to understand these flows by doing laboratory experiments. In the present paper we discuss two rather new laboratory experiments designed to study certain aspects of the atmospheric circulation. One of the experiments, the differentially heated rotating annulus at the Brandenburg University of Technology (BTU) Cottbus, has a cooled inner cylinder and a heated outer wall. However, the structure of the atmospheric meridional circulation motivates a variation of this “classical” design. In the second experiment described, operational at the Institute of Continuous Media Mechanics (ICMM) in Perm, heating and cooling is performed at different vertical levels that resembles more the atmospheric situation. Recent results of both experiments are presented and discussed. Differences and consistencies are highlighted. Though many issues are still open we conclude that both setups have their merits. The variation with heating and cooling at different levels might be more suited to study processes in the transition zone between pure rotating convection and the zone of westerly winds. On the other hand, the simpler boundary conditions of the BTU experiment make this experiment easier to control.