@phdthesis{Hasanuzzaman2021, author = {Hasanuzzaman, Gazi}, title = {Experimental investigation of turbulent boundary layer with uniform blowing at moderate and high Reynolds numbers}, doi = {10.26127/BTUOpen-5566}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-55660}, school = {BTU Cottbus - Senftenberg}, year = {2021}, abstract = {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.}, subject = {Turbulent boundary layer; Drag reduction; Particle Image Velocimetry (PIV); Laser Doppler Anemometry (LDA); Friction drag; Turbulente Grenzschicht; Particle Image Velocimetry; Laser-Doppler-Anemometrie; Mikro-Ausblasen; Reibungswiderstand; Turbulente Grenzschicht; Particle-Image-Velocimetry; Reibungswiderstand; Laser-Doppler-Anemometrie; Ausblasen}, language = {en} } @misc{Hasanuzzaman2014, type = {Master Thesis}, author = {Hasanuzzaman, Gazi}, title = {Experimental investigation and CFD analysis of wind energy estimation considering building integrated ducts}, doi = {10.26127/BTUOpen-6192}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-61928}, school = {BTU Cottbus - Senftenberg}, year = {2014}, abstract = {Wind energy is a growing concern over the present awareness of lethal impact of green house gas emission. This energy source has been proven a promising alternative to fossil fuel based energy. Increased onshore wind capacity and decreased amount of low roughness wind sites has inspired the wind energy researchers to explore the possibilities of wind energy from high roughness sites such as urban area. Moreover, exhausted grid capacity between the wind energy producer from remote area and the consumer at city is also a major constrain for wind energy expansion. Driven by such motivation, this thesis has explored possibilities of wind energy conversion from buildings where energy is needed the most. Urban topography is known to be highly turbulent region considering its roughness characteristics. Wind energy yield from urban aerodynamics is a vast arena of experimental research. Within the time frame of the thesis period and available opportunities, a brief description about the wind energy assessment modelling approach from urban flow was outlined. There are several possibilities of wind energy yield from the built structure, but only building integrated duct was focused in this thesis. Time-averaged and global wind speed on the building integrated ducts, flow around the buildings was measured from wind tunnel and numerical analysis. Available wind energy yield and turbulence present in the locations measured from the flow was calculated based on the wind tunnel data and summarized with the pros and cons of the particular geometry. Elliptical duct configuration was found to achieve maximum energy yield from the omnidirectional free stream flow. However, simple rectangular duct configuration was determined as most efficient and optimized considering its simplicity, financial feasibility and relative energy yield with other duct configuration. The thesis also showed that on roof configuration is also very promising for wind energy exploration from the omnidirectional free stream flow. Necessary recommendations were made based on available result for future development of the research approach. Scope and opportunities was mentioned. This investigation has proved that it is possible to extract limited amount of wind energy from building augmented ducts using concentrator effect of the building exterior. Thus, the thesis concluded that the wind energy yield from building augmented ducts using the concentrator effect of the building exterior is a promising renewable energy source.}, subject = {Atmospheric boundary layer; Wind energy; Laser Doppler Anemometry; Numerical simulation; Computational Fluid Mechanics; Atmosph{\"a}rische Grenzschicht; Windenergie; LDA; Numerische Simulation; Windkanal; Windenergie; Windkanal; Atmosph{\"a}rische Grenzschicht; Laser-Doppler-Anemometrie; Numerische Str{\"o}mungssimulation}, language = {en} } @phdthesis{Butt2013, author = {Butt, Mohammad Usman}, title = {Experimental investigation of the flow over macroscopic hexagonal structured surfaces}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-30555}, school = {BTU Cottbus - Senftenberg}, year = {2013}, abstract = {The flow over macroscopic patterned/structured surfaces was investigated in a subsonic wind tunnel over Reynolds numbers ranging from 3.14 x 104 to 2.77 x 105 for cylinders and from 5.34 x 105 to 11.27 x 106 for plates. The investigations were accomplished by measuring local and global drag, velocity profiles and by visualization of the flow above the surface. The investigations on structured cylinders revealed that a cylinder with outwardly curved structures has a drag coefficient of about 0.65 times of a smooth one. Flow visualization was carried out by using oil-film technique and velocity profile measurements to elucidate the observed effect, and hence present the mechanism responsible for the observed drag reduction. The near-wall velocity profiles above the surface revealed that a hexagonal bump induces local separation generating large turbulence intensity along the separating shear layer. Due to this increased turbulence, the flow reattaches to the surface with a higher momentum and become able to withstand the pressure gradient delaying the main separation significantly. Besides that, the separation does not appear to occur in a straight line along the length of the cylinder, but follow the curved path forming a wave with its crest at 115° and trough at 110°, in contrast to the laminar separation line at 85° on a smooth cylinder. Investigations on structured plates were performed with the help of hot wire anemometry and oil film interferometry. The main concern of the experiments on structured plates was to examine the effect of hexagonal structures on local and global drag of a structured plate. It was accomplished by determining and analyzing the boundary layer quantities like shear stress velocities, shear stress coefficients and momentum thicknesses over a selected Reynolds number range and various locations in streamwise direction. The results indicate that the values of shear stress coefficients measured by the conventional Clauser chart method are up to 13\% higher than the ones deduced by the Oil film Interferometry. Additionally, a maximum of 19\% reduction in shear stress coefficient behind the inwardly curved structured plate was observed. On the other hand, a dramatic increase of about 120\% in global drag coefficient supersedes the observed reduction in shear stresses at rear of the test plates. Investigations on individual hexagonal structures by measuring the shear stresses and the pressure distribution above the surface revealed that an uneven pressure distribution contributing in total drag force is responsible for a huge increase in global skin drag coefficient. Finally, a number of configurations of a wind turbine made of smooth and structured blades were investigated to compare their efficiencies at various flow velocities. No significant deviation in the efficiencies was observed.}, subject = {Aerodynamics; Oil film interferometry; Drag reduction; Hot wire anemometry; Aerodynamik; {\"O}l-Film Interferometrie; Widerstandsreduzierung; Hitzdraht Anemometrie; Hitzdrahtanemometer; Turbulente Grenzschicht; Str{\"o}mungsfeld; Str{\"o}mungsmesstechnik}, language = {en} } @phdthesis{Kessler2024, author = {Keßler, Raphael}, title = {Entwicklung eines raumflugf{\"a}higen Moduls zur optischen Untersuchung weicher Materie unter Schwerelosigkeit}, doi = {10.26127/BTUOpen-6696}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-66960}, school = {BTU Cottbus - Senftenberg}, year = {2024}, abstract = {Mit dem Begriff „weiche Materie" wird eine Stoffklasse bezeichnet, die uns im Alltag st{\"a}ndig und nahezu {\"u}berall begegnet. Dennoch z{\"a}hlt die Erforschung solcher Materialsysteme zu einer noch recht jungen Disziplin moderner Materialforschung. Dem Ziel, ein besseres Verst{\"a}ndnis und Vorhersehbarkeit mechanischer Eigenschaften zu gewinnen, gehen Kenntnisse {\"u}ber die innere Dynamik voraus. Die Dynamik in solchen Systemen wird dabei von vergleichsweise geringen Kr{\"a}ften getrieben, die bei Untersuchungen auf der Erde von dominant erscheinenden schwerkraftgetriebenen Ph{\"a}nomenen wie beispielsweise der Sedimentation {\"u}berlagert werden k{\"o}nnen. In der vorliegenden Arbeit wird die Entwicklung einer Anlage beschrieben, die eine modulare Experimentplattform auf einer H{\"o}henforschungsrakete darstellt und Experimente zur Untersuchung weicher Materie unter nahezu g{\"a}nzlicher Ausschaltung der Schwerkraft erm{\"o}glicht. Ein druckdichter und wiederverwendbarer Rumpf stellt den Experimenten auch w{\"a}hrend des Fluges atmosph{\"a}rische Bedingungen zur Verf{\"u}gung, wobei durch eine Luke nicht langzeitstabile Proben kurz vor Start der Rakete integriert werden k{\"o}nnen. H{\"a}ufig genutzte Diagnostikelemente von Lichtstreuexperimenten und Servicesystemkomponenten zur Versorgung mit Energie und Informationen werden in eine Baugruppe geb{\"u}ndelt und {\"u}ber definierte Schnittstellen f{\"u}r Neuentwicklungen zug{\"a}nglich gemacht, sodass deren Entwicklungszeiten verk{\"u}rzt werden k{\"o}nnen. Exemplarisch werden zwei Lichtstreuexperimente entwickelt und in das Modul integriert: Ein kolloidaler Teil, der die Bewegung aktiver Mikroschwimmer untersucht, und einen granularen Teil, bei dem Licht an Teilchen und Gasblasen gestreut wird. Die phototaktisch getriebenen Mikroschwimmer zeigen ohne die auf der Erde unvermeidlichen Randschichteffekte unter Mikrogravitation eine messbar verschiedene Dynamik. Mit einer kritischen Bewertung werden Verbesserungspotentiale aufgelistet, die teils im Zweitflug umgesetzt werden. F{\"u}r zuk{\"u}nftige Anwendungen auf der Experimentplattform werden Ideen und Vorhaben im Kontext der M{\"o}glichkeiten aufgef{\"u}hrt, wobei der Nutzen und der Mehrwert eines wiederfliegenden Moduls an Hand von Ergebnissen aus den stattgefundenen Fl{\"u}gen manifestiert werden k{\"o}nnen.}, subject = {Mikrogravitation; H{\"o}henforschungsrakete; Weiche Materie; Microgravity; Sounding rockets; Soft matter; H{\"o}henforschungsrakete; Weiche Materie; Mikrogravitation}, language = {de} }