Rifki Rifki

*† ‡ § The flow-field around surface-mounted obstacles has been extensively investigated over the years. The flow-field also is strongly influenced by ‘geometric’ factors as well, including ‘aspect ratio’ and ‘sweep’ of the obstacle. The influence of aspect ratio of a streamlined surface mounted obstacle on the flow in its plane of symmetry has been the objective of this investigation. The vortex system was qualitatively studied using hydrogen bubbles and laserinduced-fluorescence. The vortex system was observed to move upstream with increasing aspect ratio, while the vortex system transitioned from a ‘static’ vortex system to oscillating/shedding systems at lower Reynolds number as the aspect ratio was increased. PIV measurements in the plane of symmetry provided additional details of the flow field. A bifurcation streamline was clearly visible for an aspect ratio of 1 with an attachment point on the obstacle surface at 58% of the height of the obstacle. However for an aspect ratio 2, the bifurcation streamline moved to about 50% of the obstacle height while the vortex system moved upstream as more fluid was entrained in the system. The strength of vortex system was also observed to be influenced by the aspect ratio. The AR=2 configuration had the largest positive and negative vorticities. Non-dimensional distance between the primary vortex and the wing leading edge and between the primary and secondary vortices showed strong correlation with the aspect ratio as well.