FG Aerodynamik und Strömungslehre
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Institute
Flow control of thermal convection using thermo electro hydrodynamic forces in a cylindrical annulus
(2019)
Flow Pattern and Heat Transfer in a Cylindrical Annulus Under 1 g and Low-g Conditions: Experiments
(2018)
Flow pattern and heat transfer in a cylindrical annulus under 1g and low-g conditions: Experiments
(2017)
Gravity wave emission from jet systems in the differentially heated rotating annulus experiment
(2019)
Inertial modes and their transition to turbulence in a differentially rotating spherical gap flow
(2016)
The mechanism of localized inertial wave excitation and its efficiency is investigated for an annular cavity rotating with Ω0 . Meridional symmetry is broken by replacing
the inner cylinder with a truncated cone (frustum). Waves are excited by individual longitudinal libration of the walls. The geometry is non-separable and exhibits wave
focusing and wave attractors. We investigated laboratory and numerical results for the Ekman number E ≈ 10−6. inclination α = 5.71◦ and libration amplitudes ε 0.2 within the inertial wave band 0 < ω < 2Ω0 . Under the assumption that the inertial waves do not essentially affect the boundary-layer structure, we use classical boundary-layer analysis to study oscillating Ekman layers over a librating wall that is at an angle α = 0 to the axis of rotation. The Ekman layer erupts at frequency ω = f∗, where f∗ ≡ 2Ω0 sin α is the effective Coriolis parameter in a plane tangential to the wall. For
the selected inclination this eruption occurs for the forcing frequency ω/Ω0 = 0.2. For the librating lids eruption occurs at ω/Ω0 = 2. The study reveals that the frequency dependence of the total kinetic energy Kω of the excited wave field is strongly connected to the square of the Ekman pumping velocity wE (ω) that, in the linear limit, becomes singular when the boundary layer erupts. This explains the frequency dependence of non-resonantly excited waves. By the localization of the forcing, the two configurations investigated, (i) frustum libration and (ii) lids together with outer cylinder in libration, can be clearly distinguished by their response spectra. Good agreement was found for the spatial structure of low-order wave attractors and periodic orbits (both characterized by a small number of reflections) in the frequency windows predicted by geometric ray tracing. For ‘resonant’ frequencies a significantly increased total bulk energy was found, while the energy in the boundary layer remained nearly constant. Inertial wave energy enters the bulk flow via corner beams, which are parallel to the characteristics of the underlying Poincaré problem. Numerical simulations revealed a mismatch between the wall-parallel mass fluxes
near the corners. This leads to boundary-layer eruption and the generation of inertial waves in the corners.
Inertial waves and wave attractors in a rotating annulus with inner or outer cylinder libration
(2013)
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.