| dc.description.abstract | The study of flow around bluff bodies such as rectangular and circular cylinders is of direct relevance to several practical applications in the marine industry. The flow past bluff bodies involves several fluid phenomena, such as separation, reattachment and vortex shedding. A large amount of investigations has been performed for the circular cylinder and for the square cylinder. However, much less attention has been dedicated to the rectangular cylinders, especially the cylinders of large aspect ratios.
The main objective in this thesis is to study the two-dimensional flow past rectangular cylinders at low Reynolds numbers by use of the CFD software OpenFOAM. Different parameters are varied, so that the effects from the aspect ratio, leading edge geometry and boundary conditions can be studied. Results such as hydrodynamic quantities together with visualisation of the separation bubbles, velocity, pressure and vorticity are presented.
The first part of this thesis is a literature review where the main theory regarding viscous fluid flow around bluff bodies is presented, and a brief introduction into computational fluid dynamics is given. The literature review concludes with a description of the OpenFOAM software.
In the second part of this thesis, the numerical set-up is presented together with the results for each flow configuration. Two different aspect ratios are used; 5:1 and 10:1. With increasing aspect ratio the flow around the cylinder changes drastically. The separation bubble on the cylinder surface grows in size with both increasing aspect ratio and Reynolds number. Over the 10:1 cylinder surface at Re=300 there is two separation bubbles present, whereas only one bubble is present for the other studies with the cylinder in infinite fluid.
Adding a curvature on the leading edge decreases the bubble size. With increasing curvature, the bubble shortens in both length and height. The same applies for the bubble at the gap-side of the cylinder when adding one or two fixed boundaries. The bubble is supressed due to the short distance between the cylinder and the wall in addition to the jet flow through the gap. This results in the smallest bubble size encountered in this study.
Based on the findings, it can be concluded that the results from the present study can be useful for future research projects. | en |
