The basic idea of this method is to move the probes mounted on the traverse system in standing water. In this study, the traverse system has been used as a second method for hot-film probe calibration. Flow facilities such as water channels and wind tunnels are generally equipped with traverse systems for automation of the experiment. Then the velocity obtained is correlated with the CTA bridge voltage. In this context, a fully automated computer program including digital image processing has been developed in MATLAB to determine the flow velocity. This method is based on the visualization of the timelines in the flow with controllable voltage pulses and determination of the distance between these timelines. The first method is to use hydrogen bubbles. ![]() The aim of this study is to present two different methods that could be used to calibrate the Constant Temperature Anemometry (CTA) with hot-film probes for low speed laminar water channel flows. Die mit TSP gewonnenen Ergebnisse werden mit temperaturunabhängigen Messmethoden ergänzt und mit Erkenntnissen aus der Literatur verglichen. Dabei liegt der Fokus auf den Einflüssen der durch die Modellheizung eingebrachten, freien Konvektion. Zudem wird die Strömung über eine zweidimensionale und eine dreidimensionale Störung bei Stufen-Reynolds-Zahlen in Höhe von 199 < Rek < 1.990 untersucht. Die dadurch auftretenden Probleme bei der Untersuchung von Phänomenen, die durch Zwangskonvektion entstehen, werden analysiert und Lösungsvorschläge unterbreitet. Diese führt bei bestimmten Versuchsparametern zur Entstehung von Mischkonvektion. Dazu wird ein mit TSP beschichtetes Modul mit integrierter Heizung entwickelt, um die für die TSP-Technik notwendige Temperaturdifferenz zwischen Modelloberfläche und Strömung zu erzeugen. Zunächst wird die Anwendbarkeit des TSP-Messsystems für Visualisierungen an einer ebenen Platte im LWK untersucht. Die in dieser Arbeit durchgeführten Experimente weisen Reynolds-Zahlen im Niedergeschwindigkeitsbereich in Höhe von 30.000 < Re < 200.000 auf. The flow dynamics turns out to be driven not only by roughness Reynolds number and geometrical aspect ratio but also by the ratio between the roughness height and the boundary layer thickens.ĭer Einsatz von Temperatursensitiver Farbe (TSP) zur Untersuchung von Transition findet im Laminarwasserkanal (LWK) des Instituts für Aerodynamik und Gasdynamik der Universität Stuttgart statt. By using miniaturized vortex generators the separation zone is suppressed and no isolated global modes are present. Global feature of the eigenmode are linked to the presence of the separation zone behind the cylindrical roughness. A detailed analysis of the flowstructures is provided and linked to the involved linear mechanisms. Perturbed direct numerical simulation reveals the pivotal role of the less steady global mode in the non-linear unsteadiness. 3D optimal forcing structures are extracted to figure out the spatial distribution linked to the resonant pulsation. Subcritical bifurcation are induced by transient growth of the energy or receptivity of stable global modes. Supercritical bifurcations has been investigated by means of global stability analysis. The flow topology induced by the presence ofcylindrical roughness and miniaturized vertex generators has been studied to uncover asymptotic and short time dynamics. This thesis aims at highlighting the limits of passive control by usingminiaturized roughness elements. Therefore, most predictions by global LST can be confirmed, but additional observations in the physical flow demonstrate that not all features can be captured adequately by global LST. The mode symmetry is varicose for thick roughness elements and a changeover from varicose to sinuous modes is observed at the critical Reynolds number for thin roughness elements. ![]() Forcing with a vibrating wire reveals the evolution of the system dynamics from an amplifier to a wavemaker when the critical Reynolds number is exceeded. Although the critical Reynolds number from theory does not match the transition Reynolds number observed in experiments, there are distinct experimental observations indicating a changeover from purely convective to absolute/global instability very close to the critical Reynolds number predicted by theory. Our experiments aim at providing a comparison to global linear stability theory (LST) by means of hot-film anemometry and particle image velocimetry. ![]() The effects of isolated, cylindrical roughness elements on laminar–turbulent transition in a flat-plate boundary layer are investigated in a laminar water channel.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |