Investigation on existence and evolution of attachment saddle point structure of 3-D separation in juncture flow

The PIV experimental investigation on attachment saddle point structure of 3-D laminar separation in juncture flow has been shown in this paper. The experimental results confirmed the existence of attachment saddle point structure in juncture flow formed by different shape of models mounted on flat plate under certain Reynolds number and boundary layer conditions. The new separation structure is different from the typical separation saddle point structure that in symmetrical plane the streamlines near the surface don't rise or separated from the surface but tend to attach to the surface, the vortex sheet does not depart from the surface but from a space singular point. Flow parameters as Reynolds number and model bluntness may influence the evolution of the separation structure from one to another. Under curtain boundary layer and model conditions, as Reynolds number is increasing the juncture flow may change from attachment saddle point structure to typical separation saddle point structure. Under curtain boundary layer and Reynolds number condition, as model bluntness is increasing the juncture flow may also change from attachment saddle point structure to typical separation saddle point structure. The attachment saddle point structure in 3-D separation flow could be taken as the generalization of Lighthill's 3-D separation mode.