FG Aerodynamik und Strömungslehre
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Climate impact of the Drake Passage opening: lessons from a minimalistic laboratory experiment
(2020)
Cooling silicon photovoltaic cells using finned heat sinks and the effect of inclination angle
(2021)
Direct numerical simulations (DNS) of inertial wave attractors have been carried out in a librating Taylor-Couette system with broken mirror symmetry in the radial-axial cross-section. The inertial wave excitation mechanism and its localisation at the edges was clarified by applying boundary layer theory. Additional resonance peaks in the simulated response spectra were found to agree with low-order wave attractors obtained by geometric ray tracing. Numerics and theory are in qualitative agreement with recent lab experiments.
Drops on cylindrical wires
(2013)
Effect of the Initial Conditions on the Growth of Thermoelectric Instabilities During Parabolic
(2019)
Enhanced outer peaks in turbulent boundary layer using uniform blowing at moderate Reynolds number
(2022)
Experimental and Numerical Investigations of Isothermal Fluid-Particle Flows in Vertical Cuvette
(2007)
Experimental investigation of active control in turbulent boundary layer using uniform blowing
(2018)
Experimental Investigation of Multiphase Flow Structure behind a Bluff Body by LDV and TFS Technique
(2006)
Experimental investigation in turbulent boundary layer flows represents one of the canonical geometries of wall bounded shear flows. Utmost relevance of such experiments, however, is applied in the engineering applications in aerospace and marine industries. In particular, continuous effort is being imparted to explore the underlying physics of the flow in order to develop models for numerical tools and to achieve flow control. Within the scope of this Ph. D. topic, application of active control method such as micro-blowing effect in the incompressible, zero pressure gradient turbulent boundary layer was investigated.
Turbulent boundary layer flow is particularly interesting as well as challenging due to the presence of different interacting scales which are increasingly becoming significant as the flow inertial conditions keeps growing. Therefore, energy content of the coherent structures in outer layer becomes stronger and necessitates measurements in relatively large Reynolds number.
Present control experiments in turbulent boundary layer can be split into two different work segments, where one is objected towards the data measurements in turbulent boundary layer over smooth surface with and without any external perturbation. Here, perturbation is applied in the form of wall normal blowing while keeping the magnitude of blowing very low compared to the free stream velocity. For the subsequent results reported here, magnitude of blowing ratio was varied between 0%~6%.
In the first part of the present thesis e.g. 0.415×10e+3≤Reτ≤1.160×10e+3, measurements were performed at the Brandenburg University of Technology wind tunnel. Non-intrusive Laser Doppler Anemometry was applied to carry out a series of measurements on a zero pressure gradient flat plate turbulent boundary layer. Blowing ratio through the perforated surface was varied between 0.17%~1.52% of the free stream velocity. To a maximum of 50% reduction in friction drag was achieved.
For the measurements on the upper range of the stated Reynolds number, were conducted at the boundary layer wind tunnel. This boundary layer wind tunnel offers a spatially developed turbulent boundary layer over a flat plate within 2.2×10e+3≤Reτ≤5.5×10e+3 with an excellent spatial resolution. With the help of Stereo Particle Image Velocimetry technique, measurement of the velocity components were obtained covering entire boundary layer in streamwise wall normal plane. In addition, time resolved measurements were also obtained in spanwise and wall-normal plane in order to look into the morphology of turbulent structures immediately above the blowing area.
Uniform blowing in wall bounded shear flows is well known for its drag reducing effects and has long been investigated ever since. However, many contemporary and former research on this topic has confirmed the drag reducing effect but very less is known regarding
how blowing is effecting the Reynolds stresses at high Reynolds number. Therefore, effect of uniform blowing has been experimentally investigated using Stereo Particle Image Velocimetry (SPIV) measurements in a zero pressure gradient turbulent boundary layer (TBL). The data presented in this literature covers a large range of high Reynolds number flow e.g. Reθ = 7500∼19763 where Reynolds number is based on the momentum thickness. Upstream blowing
was varied from 1%∼6% of free stream velocity and measurements were taken downstream after a short interval. Logarithmic and outer region of the TBL was given special attention in terms of investigating statistics and turbulence properties.
Experimental study of inertial waves in a spherical shell induced by librations of the inner sphere
(2015)
Experimental study on thermal convective instabilities in the rotating wide spherical gap flow
(2001)
In aktuellen mikro-elektronischen Systemen müssen verschiedene aktive und passive Bauteile auf engstem Raum miteinander auf dem Substrate (bspw. FR4-Leiterplatte) kombiniert werden. Die dabei stetig steigende Leistungsdichte bedarf einer optimierten Kühlstrategie und der Definition von konduktiven und konvektiven Entwärmungspfade, die bereits während der Layout-Designphase der Baugruppe berücksichtigt werden sollten. Strömungsmechanische Simulationen (CFD) können dabei ein erstes Abbild zur Analyse von Kopplungseffekten zwischen den Wärmequellen und der Umgebung liefern. Diese sind jedoch oft zeitaufwendig und es bedarf zumindest ein gewisses Grundverständnis, um die Fluid-mechanischen Parameter, das Vernetzen der Geometrien und die gewonnenen Ergebnisse korrekt zu interpretieren. Erste analytische Ansätze zur reduzierten Beschreibung von ungehäusten Chips auf Leiterplattensubstrat können durch thermische Widerstandsnetzwerke abgebildet und durch Aufteilung der Wärmeströme in Richtung Substrat (Wärmeleitung) und in Richtung des bewegten Fluides (Konvektion) näher beschrieben werden.