Saddle point of separation/attachment and topology transition in laminar juncture flows

Laminar juncture flow is numerically studied to investigate the outermost saddle point of separation/attachment (S_S/S_A) and the topological transition. The topological transition trends obtained through computational results are in close agreement with the experiments. The outermost topology in the symmetry plane tends to transform from attachment to separation as the obstacle shape bluntness increases or as the ratio of the boundary layer thickness to the maximum width of the obstacle δ/W decreases. A coefficient C_S/A based on Lighthill’s volume flow theory is devised to estimate the separation or attachment of the fluid. The newly proposed criterion is applied to the limiting streamlines, very close to the flat surface, in the vicinity of saddle point to decide its topological nature. A single quadrant around the saddle point is considered for detailed theoretical analysis, and its further division into four subzones facilitates the application of the proposed criterion (C_S/A) to assess the flow attachment and separation characteristics. The decisive coefficient is successfully applied at various locations with separation/attachment flow configurations and found consistent with the qualitative results.