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

  • Bo HuEmail author
  • Hua Zhang
  • Muhammad Yamin Younis
Regular Paper


Laminar juncture flow is numerically studied to investigate the outermost saddle point of separation/attachment (SS/SA) 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 CS/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 (CS/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.

Graphical Abstract


Separation/attachment Saddle point Topology transition Topological criterion Three-dimensional (3-D) juncture flow 



The project is supported by the Natural Science Foundation of China (Grant Nos. 11372027 and 10872022).


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Copyright information

© The Visualization Society of Japan 2019

Authors and Affiliations

  1. 1.Department of Engineering MechanicsShijiazhuang Tiedao University (STDU)ShijiazhuangPeople’s Republic of China
  2. 2.Innovation Center for Wind Engineering and Wind Energy Technology of Hebei ProvinceShijiazhuangPeople’s Republic of China
  3. 3.Ministry-of-Education Key Laboratory of Fluid Mechanics, School of Aeronautical Science and EngineeringBeihang University (BUAA)BeijingPeople’s Republic of China
  4. 4.Department of Mechanical EngineeringMirpur University of Science and Technology (MUST)MirpurPakistan

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