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Experimental investigation of flow separation from rigid walls with salient edges

2004
Akçalı, Fikri
This thesis presents the experimental results on the formation of flow separation from a rigid wall with a salient edge. In the case of automotive vehicles or aircrafts with rear cargo compartment doors, such salient edges are at the origin of separated wake flows resulting in increased drag and other disturbing effects. Recent studies of Ahmed et al. (1984) on simplified geometries showed the strong influence of the slant angle on the flow separations. In this study, the geometry is further simplified to examine the flow separation under two-dimensional conditions. The experimental configuration consists of a fixed horizontal front panel and an attached rear panel with variable slant angle. The experiments were carried out in a low speed water channel to analyze the flow structure by flow visualization techniques. The hydrogen bubble technique nd PIV measurements are used to obtain both qualitative and quantitative information on the flow structure. The electrolytic precipitation technique is used to analyze the flow separation in more detail. The slant angle varied between 0 and 35 degrees while the Reynolds numbers of the model was fixed to 24800 and 50500. As a function of slant angle and Reynolds number, two different types of flow separation were observed: boundary layer separation due to adverse pressure gradient and the so called أinertial separationؤ at the edge singularity. Future strategies to control the formation of the wake flow highly depend on the very different flow structure of these two types of separation.