Investigation of different aspects of laminar horseshoe vortex system using PIV

Abstract

Juncture flow is a classical fluid mechanics problem having wide applications in both aero and hydro dynamics. The flow separates upstream of the obstacle due to the adverse pressure gradient generated by it, with the formation of the vortical structure called “horseshoe vortex.” The current study is carried out for an elliptical leading edge obstacle placed on a flat plate to investigate the horseshoe vortex for a range of Reynolds number (ReW) based on maximum width (W) for which the incoming boundary layer is laminar. Four different types of horseshoe vortex systems were found: the steady, amalgamation, transition and breakaway. The transition vortex system is one after which the vortex system changes from amalgamation to breakaway. In this phase the vortex system alternatively undergoes both amalgamation and breakaway vortex cycles. The effect of variation in the chord wise shape of the obstacle is investigated. The quantitative measurements of PIV show that the vortex system does not undergo any significant change for different chord lengths of the model with the fixed aspect ratio and maximum width. The most upstream saddle point is also studied for steady horseshoe vortex region and found that it is the “saddle of attachment” where flow attaches to the plate surface instead of separating from it.